diff --git a/.devcontainer/post-create.sh b/.devcontainer/post-create.sh
index 40ecb6e9f..fa606c5b5 100755
--- a/.devcontainer/post-create.sh
+++ b/.devcontainer/post-create.sh
@@ -76,7 +76,7 @@ log "fetching envtest binaries for K8s 1.36.2"
 # ---------- Go module cache warmup ----------
 # Go modules from go.work. Derived from 'use' entries in go.work.
 # Keep in sync with go.work when adding/removing modules.
-for m in agent api audit-syslog-bridge capture-sidecar gameaction gameproto mcp-server netguard operator sentinel svcutil telemetry-receiver telemetryschema test/e2e tunnel; do
+for m in agent api audit-syslog-bridge capture-sidecar gameaction gameproto i18n mcp-server netguard operator sentinel svcutil telemetry-receiver telemetryschema test/e2e tunnel; do
 	log "go mod download ($m)"
 	( cd "$m" && go mod download )
 done
diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 6eaee29fb..1b5a3736c 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -186,6 +186,20 @@ updates:
       telemetryschema-minor-patch:
         update-types: ["minor", "patch"]
 
+  - package-ecosystem: "gomod"
+    directory: "/i18n"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+      time: "03:00"
+    commit-message:
+      prefix: "chore(deps)"
+      include: "scope"
+    open-pull-requests-limit: 5
+    groups:
+      i18n-minor-patch:
+        update-types: ["minor", "patch"]
+
   - package-ecosystem: "gomod"
     directory: "/telemetry-receiver"
     schedule:
diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index c0f75cc41..4e4050014 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -123,6 +123,7 @@ jobs:
               - 'audit-syslog-bridge/**'
               - 'telemetry-receiver/**'
               - 'telemetryschema/**'
+              - 'i18n/**'
               - 'sentinel/**'
               - 'mcp-server/**'
               - 'capture-sidecar/**'
@@ -136,7 +137,9 @@ jobs:
               - '**/go.sum'
               - '**/Dockerfile'
             web:
+              # Language packs feed the dashboard build and the i18n checks in the web job.
               - 'web/**'
+              - 'i18n/**'
             charts:
               - 'charts/**'
               # The chart embeds a copy of the root signing key; the drift
@@ -604,7 +607,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        module: [netguard, gameaction, gameproto, telemetryschema, operator, agent, api, sentinel, audit-syslog-bridge, telemetry-receiver, mcp-server, capture-sidecar, svcutil, tunnel, gp-module, test/e2e]
+        module: [netguard, gameaction, gameproto, telemetryschema, i18n, operator, agent, api, sentinel, audit-syslog-bridge, telemetry-receiver, mcp-server, capture-sidecar, svcutil, tunnel, gp-module, test/e2e]
         exclude: ${{ fromJSON(needs.changes.outputs.lint-exclude) }}
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -683,7 +686,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        module: [netguard, gameaction, gameproto, telemetryschema, operator, api, agent, audit-syslog-bridge, telemetry-receiver, sentinel, mcp-server, capture-sidecar, svcutil, tunnel, gp-module]
+        module: [netguard, gameaction, gameproto, telemetryschema, i18n, operator, api, agent, audit-syslog-bridge, telemetry-receiver, sentinel, mcp-server, capture-sidecar, svcutil, tunnel, gp-module]
         exclude: ${{ fromJSON(needs.changes.outputs.go-exclude) }}
         arch: [amd64, arm64]
     steps:
@@ -796,6 +799,60 @@ jobs:
       - uses: actions/setup-node@949feb2413d6458794dcd2491c4babbbce0c15c1 # v7.1.0
         with: { node-version: "24", cache: "npm", cache-dependency-path: web/package-lock.json }
       - run: npm ci
+      - uses: ./.github/actions/go-cache
+        with:
+          key-suffix: web-i18n
+      - name: i18n language manifest
+        # The listing rule (80% complete, ltr, not en-XA) lives in the shared
+        # Go checker, so the manifest the dashboard build reads comes from it.
+        run: npm run i18n:manifest
+      - name: i18n checks
+        working-directory: .
+        env:
+          BASE_SHA: ${{ github.event.pull_request.base.sha || github.event.before }}
+        run: |
+          set -euo pipefail
+          (cd web && npm run i18n:extract-only)
+          (cd api && go run ./cmd/messages-export > "$RUNNER_TEMP/registry.json")
+          base_flag=()
+          if [ -n "${BASE_SHA:-}" ] && [ "$BASE_SHA" != "0000000000000000000000000000000000000000" ]; then
+            if git fetch --no-tags --depth=1 origin "$BASE_SHA" 2>/dev/null \
+              && git cat-file -e "$BASE_SHA:i18n/locales" 2>/dev/null; then
+              mkdir -p "$RUNNER_TEMP/base"
+              git archive "$BASE_SHA" i18n/locales | tar -x -C "$RUNNER_TEMP/base"
+              base_flag=(--base "$RUNNER_TEMP/base/i18n/locales")
+            fi
+          fi
+          cd i18n
+          go run ./cmd/i18n-check \
+            --extracted ../web/src/generated/i18n/extracted.json \
+            --registry "$RUNNER_TEMP/registry.json" --check-server \
+            "${base_flag[@]}" \
+            --summary "$GITHUB_STEP_SUMMARY" \
+            locales
+      - name: i18n-check self-test on seeded defective packs
+        # SC-007: every fixture must make the checker fail with exactly its
+        # own finding code (needs-review is a notice, so it passes).
+        working-directory: i18n
+        run: |
+          set -euo pipefail
+          go build -o "$RUNNER_TEMP/i18n-check" ./cmd/i18n-check
+          for dir in testdata/defective/*/; do
+            code=$(basename "$dir")
+            args=()
+            if [ -f "$dir/args" ]; then
+              read -r -a args < <(sed "s#{dir}#${dir%/}#g" "$dir/args")
+            fi
+            set +e
+            out=$("$RUNNER_TEMP/i18n-check" "${args[@]}" "${dir%/}")
+            status=$?
+            set -e
+            want=1; [ "$code" = needs-review ] && want=0
+            if [ "$status" -ne "$want" ] || ! grep -q "\[$code\]" <<<"$out"; then
+              echo "::error::fixture $code: exit $status (want $want), output:"; echo "$out"; exit 1
+            fi
+            echo "ok $code"
+          done
       - name: eslint
         run: npm run lint
       - run: npm run build
diff --git a/.github/workflows/publish-edge.yaml b/.github/workflows/publish-edge.yaml
index 11ac55918..1c119a396 100644
--- a/.github/workflows/publish-edge.yaml
+++ b/.github/workflows/publish-edge.yaml
@@ -29,6 +29,7 @@ on:
       - "gameaction/**"
       - "gameproto/**"
       - "telemetryschema/**"
+      - "i18n/**"
       - "svcutil/**"
       - "gp-module/**"
       - "audit-syslog-bridge/**"
diff --git a/.gitignore b/.gitignore
index bbf734e0f..d41515d4b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -25,6 +25,12 @@ web/coverage/
 web/playwright-report/
 web/test-results/
 web/website-screenshots/
+# Generated i18n artifacts (compiled catalogs, extracted messages, language manifest)
+web/src/generated/
+# Registry snapshot written by `make i18n-sync` and consumed by i18n-check
+i18n/.registry.json
+# Filtered language packs written by i18n-check --valid-out for the dashboard build
+i18n/.valid/
 web/e2e/.portforward.pid
 *.log
 .npmrc.local
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 33a5a20d1..bfd3709ef 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -118,6 +118,36 @@ reaches `1.0.0`. Pre-1.0 minor versions may contain breaking changes.
 - **Nuclear Option player lists are structured:** the agent's player output
   for JSON player lists now includes an entry per player (`steamId` and
   `faction`), which the API uses for display-name lookup.
+- **Language selection and translations (spec 019):** the dashboard can be
+  shown in another language. A user's language choice is saved to the account (or
+  to the browser when signed out), and an admin sets the instance default. Languages are
+  shared packs under `i18n/locales/`; a language is listed once its pack is at
+  least 80% translated, and anything missing falls back to English. French is
+  the first pack and is listed once it reaches 80%.
+  Dates, numbers and relative times follow the active language. A pseudo
+  language (`en-XA`) exists for maintainers behind `VITE_I18N_PSEUDO=1` and is
+  never listed in a release. See [`docs/translating.md`](docs/translating.md).
+- **Translated server messages (opt-in `problem+json`):** API errors are sent
+  as `application/problem+json` with a stable `messageId` and arguments only
+  when the request lists that type in `Accept`; every other client keeps the
+  unchanged English plain-text body. The dashboard opts in and shows the
+  message in the active language. Game server condition messages carry
+  `status.conditionArgs` so the dashboard can translate them too; the English
+  `message` is unchanged.
+- **Notification language per destination:** each notification destination
+  has an optional `language`; notifications and test sends to Discord, email
+  and webhooks are rendered in it, and destinations with none use the
+  instance default. Webhook payloads gain additive `language`, `title` and
+  `text` fields; existing fields are unchanged.
+- **Module translations:** a module can ship `locales/<tag>.json` next to
+  `module.yaml` (OCI layer type `application/vnd.gameplane.module.locale.v1+json`
+  and the same files in every other source). The operator validates them on
+  install, stores the valid entries in a `<template>-locales` ConfigMap and
+  reports problems as the `LocalesValid` condition; install never fails
+  because of translations. Each file is read up to 900 KiB and all of a
+  bundle's files together up to 4 MiB. `gp-module i18n extract|stamp` and
+  `gp-module validate` support authoring. See
+  [`docs/module-authoring.md`](docs/module-authoring.md).
 
 ### Changed
 
diff --git a/CLAUDE.md b/CLAUDE.md
index 4ad438ad5..21718e9bc 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -36,6 +36,7 @@ netguard/            SSRF dial-guard: IsAllowed (operator module sources, API si
 gameaction/          console-injection guard + command renderer (api, agent)
 gameproto/           Minecraft/Terraria handshake parser (sentinel)
 telemetryschema/     shared telemetry report contract (api, telemetry-receiver)
+i18n/                shared language packs, ICU formatter, pack validator, i18n-check (api, web, operator, gp-module)
 gp-module/           module authoring CLI: init/validate/preview/package
 operator/            controller-runtime operator
   api/v1alpha1/      CRD types (edit here, then `make generate manifests`); zz_generated.deepcopy.go GENERATED
@@ -60,7 +61,7 @@ test/e2e/            Kind E2E suite (//go:build e2e)
 docs/                architecture, security, modules
 design.pen           canonical Pencil dashboard design
 signing/             cosign public keys, dated legacy key + cross-signature (image + module)
-go.work              links all 16 Go modules (incl. test/e2e)
+go.work              links all 17 Go modules (incl. test/e2e)
 Makefile             canonical task runner
 ```
 
@@ -75,7 +76,7 @@ After cloning: `git submodule update --init` (`modules/` required for `make dev-
 - **E2E conventions:** register new tests in `test/e2e/buckets.sh`; `t.Parallel()` + unique names; guard shared resources (`ociPushMu` for module pushes, `ensureResticRepo(t)` for shared backup repos). Rate limits per cluster: IP burst 10 (5/min), user burst 6 (3/min) — cap an API bucket at ~7 admin logins.
 - **Lint:** `make lint` = gofmt, go vet, golangci-lint, ESLint, `check-specs`, `check-doc-versions`, `check-links`.
 
-**Coverage minimums:** netguard 91, gameaction 91, gameproto 90, telemetryschema 90, gp-module 80, operator 72, api 80, agent 90, svcutil 90; audit-syslog-bridge, telemetry-receiver, sentinel, capture-sidecar, mcp-server, tunnel 70; web 92 lines / 76 functions / 82 branches / 92 statements.
+**Coverage minimums:** netguard 91, gameaction 91, gameproto 90, telemetryschema 90, i18n 90, gp-module 80, operator 72, api 80, agent 90, svcutil 90; audit-syslog-bridge, telemetry-receiver, sentinel, capture-sidecar, mcp-server, tunnel 70; web 92 lines / 76 functions / 82 branches / 92 statements.
 
 ## Core rules
 
@@ -116,6 +117,7 @@ After cloning: `git submodule update --init` (`modules/` required for `make dev-
 | gameaction | Go | validates console input against schemas; escapes injection |
 | gameproto | Go | Minecraft/Terraria wire parser for connection filtering |
 | telemetryschema | Go | stdlib-only shared telemetry report contract: types, strict decode, official module catalog, report signing (api, telemetry-receiver) |
+| i18n | Go | shared language packs (`go:embed`), ICU MessageFormat subset, pack validator, `i18n-check` CI tool (api, web, operator, gp-module) |
 | gp-module | Go | module CLI: scaffold, offline validate, dry-run preview, OCI package |
 | svcutil | Go | stdlib-only env + graceful shutdown (`RunHTTP`) |
 | operator | Go, controller-runtime | authoritative reconciler for 9 CRDs (`GameServer`, `GameTemplate`, …) |
diff --git a/Makefile b/Makefile
index 02f0df3fe..50a800cdd 100644
--- a/Makefile
+++ b/Makefile
@@ -40,7 +40,7 @@ KUBECONFIG_ENV :=
 KUBE_CONTEXT   := kind-$(KIND_CLUSTER)
 endif
 
-GO_MODULES     := netguard gameaction gameproto telemetryschema gp-module operator api agent audit-syslog-bridge telemetry-receiver sentinel mcp-server capture-sidecar svcutil tunnel
+GO_MODULES     := netguard gameaction gameproto telemetryschema i18n gp-module operator api agent audit-syslog-bridge telemetry-receiver sentinel mcp-server capture-sidecar svcutil tunnel
 GO_INTEGRATION_MODULES := operator api
 
 # test/e2e is a separate module (its own go.mod, excluded from the coverage
@@ -259,6 +259,20 @@ check-links: ## Verify internal documentation links and anchors resolve
 check-telemetry-catalog: ## Verify telemetryschema/catalog.txt matches the chart's official module list
 	hack/check-telemetry-catalog.sh
 
+.PHONY: i18n-sync
+i18n-sync: ## Write the API message registry (server.* and notify.*) and the operator condition.* ids into the English reference (i18n/locales/en/app.json)
+	cd api && go run ./cmd/messages-export > ../i18n/.registry.json
+	cd i18n && go run ./cmd/i18n-check --registry .registry.json --sync-server locales
+	rm -f i18n/.registry.json
+	cd operator && go run ./hack/condition-ids -app ../i18n/locales/en/app.json
+
+.PHONY: check-i18n
+check-i18n: ## Verify language packs, server.*, notify.* and operator condition.* drift and dashboard extraction drift (spec 019)
+	cd web && npm run i18n:extract-only
+	cd operator && go run ./hack/condition-ids -check -app ../i18n/locales/en/app.json
+	cd api && go run ./cmd/messages-export > ../i18n/.registry.json
+	cd i18n && status=0; go run ./cmd/i18n-check --extracted ../web/src/generated/i18n/extracted.json --registry .registry.json --check-server locales || status=$$?; rm -f .registry.json; exit $$status
+
 .PHONY: check-dev-load-images
 check-dev-load-images: ## Verify `dev-load` loads every image `images` builds
 	hack/check-dev-load-images.sh
@@ -273,7 +287,7 @@ test-up-registry: ## Run the fixture tests for deploy/kind/up.sh's registry/cont
 	hack/test-up-registry.sh
 
 .PHONY: lint
-lint: check-doc-versions check-links check-specs check-telemetry-catalog check-dev-load-images check-coverage-gaps test-up-registry lint-go lint-web ## Run all linters
+lint: check-doc-versions check-links check-specs check-telemetry-catalog check-i18n check-dev-load-images check-coverage-gaps test-up-registry lint-go lint-web ## Run all linters
 
 .PHONY: lint-go
 lint-go: ## Run golangci-lint across all modules
diff --git a/README.md b/README.md
index c33345f38..09c7f0c44 100644
--- a/README.md
+++ b/README.md
@@ -285,6 +285,9 @@ Design changes go through `design.pen` (Pencil) before any UI code is
 written. See [`docs/contributing.md`](docs/contributing.md) for the
 full guide: code style, test tiers, and the PR process.
 
+Translations are welcome. See [`docs/translating.md`](docs/translating.md)
+to add or improve a language pack.
+
 ## License
 
 [AGPL-3.0-or-later](./LICENSE). Any network-accessible deployment of a
diff --git a/api/Dockerfile b/api/Dockerfile
index 1613efe8a..fb699ff47 100644
--- a/api/Dockerfile
+++ b/api/Dockerfile
@@ -1,13 +1,14 @@
 FROM --platform=$BUILDPLATFORM golang:1.27-alpine AS build
 WORKDIR /src
 
-# netguard, gameaction, gp-module, and telemetryschema are in-repo modules the API depends
-# on via local replaces (../netguard, ../gameaction, ../gp-module, ../telemetryschema);
+# netguard, gameaction, gp-module, telemetryschema, and i18n are in-repo modules the API depends
+# on via local replaces (../netguard, ../gameaction, ../gp-module, ../telemetryschema, ../i18n);
 # copy them first so `go mod download` and the build resolve them.
 COPY netguard/ ./netguard/
 COPY gameaction/ ./gameaction/
 COPY gp-module/ ./gp-module/
 COPY telemetryschema/ ./telemetryschema/
+COPY i18n/ ./i18n/
 COPY api/go.mod api/go.sum* ./api/
 WORKDIR /src/api
 RUN go mod download
diff --git a/api/cmd/main.go b/api/cmd/main.go
index 56990e0a4..ec996b4a1 100644
--- a/api/cmd/main.go
+++ b/api/cmd/main.go
@@ -331,6 +331,10 @@ func main() {
 		// registry per request so config saves apply without a restart.
 		// No version/host/count — login-privacy.
 		r.Get("/providers", handlers.AuthProvidersHandler(authRegistry))
+		// Pre-auth: the instance default language for the login page. Only the
+		// tag is returned, never more (login privacy); not rate-limited, like
+		// /providers.
+		r.Get("/locale", handlers.AuthLocaleHandler(store))
 		// Rate-limit /login specifically — argon2id is ~200 ms of
 		// single-core CPU per attempt, so an unlimited path invites a
 		// trivial DoS.
diff --git a/api/cmd/messages-export/main.go b/api/cmd/messages-export/main.go
new file mode 100644
index 000000000..a40a6fc2e
--- /dev/null
+++ b/api/cmd/messages-export/main.go
@@ -0,0 +1,19 @@
+// Command messages-export writes the API message registry as JSON to stdout,
+// together with the notify.* notification text. The i18n-sync Makefile target
+// feeds the output to i18n-check.
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
+	"github.com/GameplanePanel/gameplane/api/internal/notify"
+)
+
+func main() {
+	if err := messages.ExportJSON(os.Stdout, notify.Messages()...); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
diff --git a/api/docs/openapi.yaml b/api/docs/openapi.yaml
index 40c1a884a..89fb097f3 100644
--- a/api/docs/openapi.yaml
+++ b/api/docs/openapi.yaml
@@ -255,6 +255,11 @@ paths:
       responses:
         '200':
           description: OK
+  '/modules/{name}/locales/{tag}':
+    get:
+      responses:
+        '200':
+          description: OK
   '/namespaces':
     get:
       responses:
diff --git a/api/go.mod b/api/go.mod
index 63013fc9d..5e147ae1f 100644
--- a/api/go.mod
+++ b/api/go.mod
@@ -29,7 +29,12 @@ require github.com/GameplanePanel/gameplane/telemetryschema v0.0.0
 // `go build ./api/...`.
 replace github.com/GameplanePanel/gameplane/telemetryschema => ../telemetryschema
 
+// i18n is an in-repo module (no published version); resolve it locally
+// both inside the go.work workspace and for standalone `go build ./api/...`.
+replace github.com/GameplanePanel/gameplane/i18n => ../i18n
+
 require (
+	github.com/GameplanePanel/gameplane/i18n v0.0.0
 	github.com/coder/websocket v1.8.15
 	github.com/coreos/go-oidc/v3 v3.21.0
 	github.com/go-chi/chi/v5 v5.3.2
@@ -43,6 +48,7 @@ require (
 	golang.org/x/oauth2 v0.37.0
 	golang.org/x/sync v0.24.0
 	golang.org/x/sys v0.49.0
+	golang.org/x/text v0.42.0
 	k8s.io/api v0.37.1
 	k8s.io/apimachinery v0.37.1
 	k8s.io/client-go v0.37.1
@@ -109,7 +115,6 @@ require (
 	go.yaml.in/yaml/v3 v3.0.5 // indirect
 	golang.org/x/net v0.59.0 // indirect
 	golang.org/x/term v0.46.0 // indirect
-	golang.org/x/text v0.42.0 // indirect
 	golang.org/x/time v0.15.0 // indirect
 	gomodules.xyz/jsonpatch/v2 v2.5.0 // indirect
 	google.golang.org/protobuf v1.36.12 // indirect
diff --git a/api/internal/auth/local.go b/api/internal/auth/local.go
index af5afaa0d..dd2a96575 100644
--- a/api/internal/auth/local.go
+++ b/api/internal/auth/local.go
@@ -9,6 +9,8 @@ import (
 	"strings"
 
 	"github.com/GameplanePanel/gameplane/api/internal/db"
+	"github.com/GameplanePanel/gameplane/api/internal/httperr"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 )
 
 // Local handles local (username/password) authentication.
@@ -105,7 +107,7 @@ type loginResp struct {
 func (l *Local) HandleLogin(sessions *SessionStore, reg *Registry) http.HandlerFunc {
 	return func(w http.ResponseWriter, req *http.Request) {
 		if reg != nil && !reg.LocalEnabled(req.Context()) {
-			http.Error(w, "login method disabled", http.StatusForbidden)
+			httperr.WriteCode(w, req, http.StatusForbidden, errors.New("login method disabled"))
 			return
 		}
 		// Enforce JSON content-type — a cross-site form POST can carry
@@ -114,12 +116,12 @@ func (l *Local) HandleLogin(sessions *SessionStore, reg *Registry) http.HandlerF
 		// the CSRF token check on the mutation path.
 		ct := req.Header.Get("Content-Type")
 		if !strings.HasPrefix(ct, "application/json") {
-			http.Error(w, "expected application/json", http.StatusUnsupportedMediaType)
+			httperr.WriteCode(w, req, http.StatusUnsupportedMediaType, errors.New("expected application/json"))
 			return
 		}
 		var body loginReq
 		if err := json.NewDecoder(req.Body).Decode(&body); err != nil {
-			http.Error(w, "bad request", http.StatusBadRequest)
+			httperr.WriteCode(w, req, http.StatusBadRequest, errors.New("bad request"))
 			return
 		}
 		// Per-username throttle layered on top of the per-IP LoginLimiter:
@@ -129,7 +131,7 @@ func (l *Local) HandleLogin(sessions *SessionStore, reg *Registry) http.HandlerF
 		// leak existence.
 		if body.Username != "" && !LoginUserLimiter.AllowUser(body.Username) {
 			w.Header().Set("Retry-After", "30")
-			http.Error(w, "too many requests", http.StatusTooManyRequests)
+			httperr.WriteCode(w, req, http.StatusTooManyRequests, errors.New("too many requests"))
 			return
 		}
 		// Every branch below that returns 401 must first spend the argon2
@@ -139,12 +141,12 @@ func (l *Local) HandleLogin(sessions *SessionStore, reg *Registry) http.HandlerF
 		u, hash, err := l.fetchUser(req.Context(), body.Username)
 		if err != nil || hash == "" {
 			VerifyDummy(req.Context(), body.Password)
-			http.Error(w, "invalid credentials", http.StatusUnauthorized)
+			httperr.WriteMessage(w, req, messages.New("server.auth.invalid_credentials", nil))
 			return
 		}
 		ok, err := VerifyPassword(req.Context(), body.Password, hash)
 		if err != nil || !ok {
-			http.Error(w, "invalid credentials", http.StatusUnauthorized)
+			httperr.WriteMessage(w, req, messages.New("server.auth.invalid_credentials", nil))
 			return
 		}
 		perms, err := sessions.LoadPerms(req.Context(), u.ID)
diff --git a/api/internal/auth/local_test.go b/api/internal/auth/local_test.go
index d9f07f159..504c8e668 100644
--- a/api/internal/auth/local_test.go
+++ b/api/internal/auth/local_test.go
@@ -3,8 +3,12 @@ package auth
 import (
 	"context"
 	"encoding/json"
+	"go/ast"
+	"go/parser"
+	"go/token"
 	"net/http"
 	"net/http/httptest"
+	"strconv"
 	"strings"
 	"testing"
 
@@ -256,3 +260,188 @@ func TestLogin_WrongPassword_LeavesAuditActorAnonymous(t *testing.T) {
 		t.Errorf("audit actor = %q, want empty", got)
 	}
 }
+
+// problemAccept is the Accept header a problem-document caller sends.
+const problemAccept = "application/json, application/problem+json"
+
+// loginWithAccept runs POST /login with a JSON body and an optional Accept
+// header, returning the recorded response.
+func loginWithAccept(t *testing.T, l *Local, ss *SessionStore, body, accept string) *httptest.ResponseRecorder {
+	t.Helper()
+	rr := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(context.Background(), "POST", "/login", strings.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	if accept != "" {
+		req.Header.Set("Accept", accept)
+	}
+	l.HandleLogin(ss, nil).ServeHTTP(rr, req)
+	return rr
+}
+
+// decodeProblemDoc decodes an RFC 9457 problem body and fails the test when
+// the response is not a problem document.
+func decodeProblemDoc(t *testing.T, rr *httptest.ResponseRecorder) map[string]any {
+	t.Helper()
+	if ct := rr.Header().Get("Content-Type"); ct != "application/problem+json" {
+		t.Fatalf("Content-Type=%q, want application/problem+json", ct)
+	}
+	var doc map[string]any
+	if err := json.Unmarshal(rr.Body.Bytes(), &doc); err != nil {
+		t.Fatalf("decode problem: %v (body %q)", err, rr.Body.String())
+	}
+	return doc
+}
+
+// TestLogin_ProblemDetails_UnknownUserAndWrongPasswordIdentical checks that a
+// problem-document caller cannot tell an unknown user from a wrong password
+// (FR-030): both get the same registered id, detail and raw body.
+func TestLogin_ProblemDetails_UnknownUserAndWrongPasswordIdentical(t *testing.T) {
+	s := newAuthDB(t)
+	seedUser(t, s, "pd-alice", "hunter2", "admin")
+	l := NewLocal(s)
+	ss := NewSessionStore(s)
+
+	unknown := loginWithAccept(t, l, ss, `{"username":"pd-nobody","password":"x"}`, problemAccept)
+	wrong := loginWithAccept(t, l, ss, `{"username":"pd-alice","password":"wrong"}`, problemAccept)
+
+	for name, rr := range map[string]*httptest.ResponseRecorder{"unknown user": unknown, "wrong password": wrong} {
+		if rr.Code != http.StatusUnauthorized {
+			t.Fatalf("%s: code=%d, want 401", name, rr.Code)
+		}
+		doc := decodeProblemDoc(t, rr)
+		if doc["messageId"] != "server.auth.invalid_credentials" {
+			t.Errorf("%s: messageId=%v", name, doc["messageId"])
+		}
+		if doc["detail"] != "invalid credentials" {
+			t.Errorf("%s: detail=%v", name, doc["detail"])
+		}
+		if args, ok := doc["args"].(map[string]any); !ok || len(args) != 0 {
+			t.Errorf("%s: args=%v, want empty object", name, doc["args"])
+		}
+	}
+	if unknown.Body.String() != wrong.Body.String() {
+		t.Fatalf("bodies differ:\n unknown=%q\n wrong=%q", unknown.Body.String(), wrong.Body.String())
+	}
+}
+
+// TestLogin_PlainTextBodyUnchanged checks that a caller without a problem
+// Accept header still gets the byte-identical plain-text body.
+func TestLogin_PlainTextBodyUnchanged(t *testing.T) {
+	s := newAuthDB(t)
+	seedUser(t, s, "pd-bob", "hunter2", "admin")
+	l := NewLocal(s)
+	ss := NewSessionStore(s)
+
+	unknown := loginWithAccept(t, l, ss, `{"username":"pd-nobody","password":"x"}`, "")
+	wrong := loginWithAccept(t, l, ss, `{"username":"pd-bob","password":"wrong"}`, "")
+
+	for name, rr := range map[string]*httptest.ResponseRecorder{"unknown user": unknown, "wrong password": wrong} {
+		if rr.Code != http.StatusUnauthorized {
+			t.Fatalf("%s: code=%d, want 401", name, rr.Code)
+		}
+		if rr.Body.String() != "invalid credentials\n" {
+			t.Errorf("%s: body=%q", name, rr.Body.String())
+		}
+		if ct := rr.Header().Get("Content-Type"); ct != "text/plain; charset=utf-8" {
+			t.Errorf("%s: Content-Type=%q", name, ct)
+		}
+	}
+}
+
+// TestLogin_OtherRejectionsUseGenericIDs checks that the non-credential
+// rejections on POST /login answer with the generic id for their status.
+func TestLogin_OtherRejectionsUseGenericIDs(t *testing.T) {
+	s := newAuthDB(t)
+	l := NewLocal(s)
+	ss := NewSessionStore(s)
+
+	wrongType := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(context.Background(), "POST", "/login", strings.NewReader("user=alice"))
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	req.Header.Set("Accept", problemAccept)
+	l.HandleLogin(ss, nil).ServeHTTP(wrongType, req)
+
+	badJSON := loginWithAccept(t, l, ss, "not json", problemAccept)
+
+	for range 6 {
+		LoginUserLimiter.AllowUser("pd-drained")
+	}
+	limited := loginWithAccept(t, l, ss, `{"username":"pd-drained","password":"x"}`, problemAccept)
+
+	cases := []struct {
+		name   string
+		rr     *httptest.ResponseRecorder
+		status int
+		detail string
+	}{
+		{"non-JSON content type", wrongType, http.StatusUnsupportedMediaType, "expected application/json"},
+		{"invalid JSON body", badJSON, http.StatusBadRequest, "bad request"},
+		{"per-user rate limit", limited, http.StatusTooManyRequests, "too many requests"},
+	}
+	for _, c := range cases {
+		if c.rr.Code != c.status {
+			t.Fatalf("%s: code=%d, want %d", c.name, c.rr.Code, c.status)
+		}
+		doc := decodeProblemDoc(t, c.rr)
+		want := "server.generic." + strconv.Itoa(c.status)
+		if doc["messageId"] != want {
+			t.Errorf("%s: messageId=%v, want %s", c.name, doc["messageId"], want)
+		}
+		if doc["detail"] != c.detail {
+			t.Errorf("%s: detail=%v, want %q", c.name, doc["detail"], c.detail)
+		}
+	}
+}
+
+// TestUnauthenticatedFilesUseOnlyGenericIDs guards FR-030 at the source
+// level: the unauthenticated login and OIDC callback files may only register
+// the invalid-credentials message, and every other error they write must be
+// a generic 5xx.
+func TestUnauthenticatedFilesUseOnlyGenericIDs(t *testing.T) {
+	for _, name := range []string{"local.go", "oidc.go"} {
+		fset := token.NewFileSet()
+		file, err := parser.ParseFile(fset, name, nil, 0)
+		if err != nil {
+			t.Fatalf("parse %s: %v", name, err)
+		}
+		ast.Inspect(file, func(n ast.Node) bool {
+			call, ok := n.(*ast.CallExpr)
+			if !ok {
+				return true
+			}
+			sel, ok := call.Fun.(*ast.SelectorExpr)
+			if !ok {
+				return true
+			}
+			pkg, ok := sel.X.(*ast.Ident)
+			if !ok {
+				return true
+			}
+			pos := fset.Position(call.Pos())
+			switch {
+			case pkg.Name == "messages" && sel.Sel.Name == "New":
+				if len(call.Args) == 0 {
+					return true
+				}
+				lit, ok := call.Args[0].(*ast.BasicLit)
+				if !ok {
+					t.Errorf("%s: messages.New with a non-literal id", pos)
+					return true
+				}
+				id, err := strconv.Unquote(lit.Value)
+				if err != nil || id != "server.auth.invalid_credentials" {
+					t.Errorf("%s: messages.New(%s) is not the invalid-credentials id", pos, lit.Value)
+				}
+			case pkg.Name == "http" && sel.Sel.Name == "Error":
+				if len(call.Args) != 3 {
+					return true
+				}
+				status, ok := call.Args[2].(*ast.SelectorExpr)
+				if !ok || status.Sel.Name != "StatusInternalServerError" {
+					t.Errorf("%s: http.Error with a status other than a 5xx selector", pos)
+				}
+			}
+			return true
+		})
+	}
+}
diff --git a/api/internal/auth/oidc.go b/api/internal/auth/oidc.go
index 777dce5bf..7f7945f84 100644
--- a/api/internal/auth/oidc.go
+++ b/api/internal/auth/oidc.go
@@ -13,6 +13,7 @@ import (
 	"golang.org/x/oauth2"
 
 	"github.com/GameplanePanel/gameplane/api/internal/db"
+	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/scope"
 )
 
@@ -385,7 +386,7 @@ func (o *OIDC) HandleCallbackAt(sessions *SessionStore, cookiePath string) http.
 	return func(w http.ResponseWriter, req *http.Request) {
 		state, err := req.Cookie(oidcStateCookie)
 		if err != nil || state.Value == "" || state.Value != req.URL.Query().Get("state") {
-			http.Error(w, "state mismatch", http.StatusBadRequest)
+			httperr.WriteCode(w, req, http.StatusBadRequest, errors.New("state mismatch"))
 			return
 		}
 		clearCookieAt(w, oidcStateCookie, cookiePath)
@@ -393,17 +394,17 @@ func (o *OIDC) HandleCallbackAt(sessions *SessionStore, cookiePath string) http.
 		tok, err := o.oauth.Exchange(req.Context(), req.URL.Query().Get("code"))
 		if err != nil {
 			slog.Warn("oidc exchange", "err", err)
-			http.Error(w, "oauth exchange failed", http.StatusBadRequest)
+			httperr.WriteCode(w, req, http.StatusBadRequest, errors.New("oauth exchange failed"))
 			return
 		}
 		rawID, _ := tok.Extra("id_token").(string)
 		if rawID == "" {
-			http.Error(w, "no id_token", http.StatusBadRequest)
+			httperr.WriteCode(w, req, http.StatusBadRequest, errors.New("no id_token"))
 			return
 		}
 		idt, err := o.verifier.Verify(req.Context(), rawID)
 		if err != nil {
-			http.Error(w, "invalid id_token", http.StatusUnauthorized)
+			httperr.WriteCode(w, req, http.StatusUnauthorized, errors.New("invalid id_token"))
 			return
 		}
 		// Nonce check — the IdP is expected to echo the nonce we issued
@@ -413,7 +414,7 @@ func (o *OIDC) HandleCallbackAt(sessions *SessionStore, cookiePath string) http.
 		nonceCookie, err := req.Cookie(oidcNonceCookie)
 		if err != nil || nonceCookie.Value == "" || idt.Nonce != nonceCookie.Value {
 			clearCookieAt(w, oidcNonceCookie, cookiePath)
-			http.Error(w, "nonce mismatch", http.StatusBadRequest)
+			httperr.WriteCode(w, req, http.StatusBadRequest, errors.New("nonce mismatch"))
 			return
 		}
 		clearCookieAt(w, oidcNonceCookie, cookiePath)
@@ -424,7 +425,7 @@ func (o *OIDC) HandleCallbackAt(sessions *SessionStore, cookiePath string) http.
 		}
 		if err := idt.Claims(&claims); err != nil {
 			slog.Warn("oidc claim parse", "err", err)
-			http.Error(w, "invalid id_token claims", http.StatusBadRequest)
+			httperr.WriteCode(w, req, http.StatusBadRequest, errors.New("invalid id_token claims"))
 			return
 		}
 		// The typed struct above can't see arbitrary claim names, so the
@@ -432,7 +433,7 @@ func (o *OIDC) HandleCallbackAt(sessions *SessionStore, cookiePath string) http.
 		var rawClaims map[string]any
 		if err := idt.Claims(&rawClaims); err != nil {
 			slog.Warn("oidc raw claim parse", "err", err)
-			http.Error(w, "invalid id_token claims", http.StatusBadRequest)
+			httperr.WriteCode(w, req, http.StatusBadRequest, errors.New("invalid id_token claims"))
 			return
 		}
 		// Extract groups using the configured claim name, defaulting to "groups" if empty.
@@ -456,7 +457,7 @@ func (o *OIDC) HandleCallbackAt(sessions *SessionStore, cookiePath string) http.
 			// Log the identity, never the tokens.
 			slog.Warn("oidc login denied: no group grants a role and defaultRole is deny",
 				"issuer", idt.Issuer, "subject", claims.Sub)
-			http.Error(w, "login not permitted", http.StatusForbidden)
+			httperr.WriteCode(w, req, http.StatusForbidden, errors.New("login not permitted"))
 			return
 		}
 
diff --git a/api/internal/auth/ratelimit.go b/api/internal/auth/ratelimit.go
index dc746f78d..2501e8281 100644
--- a/api/internal/auth/ratelimit.go
+++ b/api/internal/auth/ratelimit.go
@@ -1,6 +1,7 @@
 package auth
 
 import (
+	"errors"
 	"net"
 	"net/http"
 	"strconv"
@@ -8,6 +9,9 @@ import (
 	"time"
 
 	"github.com/go-chi/chi/v5/middleware"
+
+	"github.com/GameplanePanel/gameplane/api/internal/httperr"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 )
 
 // TokenBucket is a minimal per-key rate limiter: each key has a bucket
@@ -98,7 +102,7 @@ func (t *TokenBucket) Middleware(next http.Handler) http.Handler {
 		}
 		if !t.Allow(clientIP) {
 			w.Header().Set("Retry-After", "30")
-			http.Error(w, "too many requests", http.StatusTooManyRequests)
+			httperr.WriteCode(w, req, http.StatusTooManyRequests, errors.New("too many requests"))
 			return
 		}
 		next.ServeHTTP(w, req)
@@ -144,12 +148,12 @@ func (t *TokenBucket) UserMiddleware(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
 		u := UserFromContext(req.Context())
 		if u == nil {
-			http.Error(w, "unauthenticated", http.StatusUnauthorized)
+			httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 			return
 		}
 		if !t.AllowUser(strconv.FormatInt(u.ID, 10)) {
 			w.Header().Set("Retry-After", "1")
-			http.Error(w, "too many requests", http.StatusTooManyRequests)
+			httperr.WriteMessage(w, req, messages.New("server.common.too_many_requests", nil))
 			return
 		}
 		next.ServeHTTP(w, req)
diff --git a/api/internal/auth/ratelimit_test.go b/api/internal/auth/ratelimit_test.go
index d78c2518a..85f2b35d1 100644
--- a/api/internal/auth/ratelimit_test.go
+++ b/api/internal/auth/ratelimit_test.go
@@ -2,6 +2,7 @@ package auth
 
 import (
 	"context"
+	"encoding/json"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -152,3 +153,26 @@ func TestTokenBucket_GC(t *testing.T) {
 		t.Fatal("stale bucket should have been GC'd")
 	}
 }
+
+func TestTokenBucketMiddleware_429IsGenericProblem(t *testing.T) {
+	b := newTokenBucket(0, 0)
+	h := b.Middleware(http.HandlerFunc(func(http.ResponseWriter, *http.Request) {}))
+	rr := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(context.Background(), "POST", "/login", nil)
+	req.RemoteAddr = "10.0.0.1:1234"
+	req.Header.Set("Accept", "application/problem+json")
+	h.ServeHTTP(rr, req)
+	if rr.Code != http.StatusTooManyRequests {
+		t.Fatalf("code=%d", rr.Code)
+	}
+	if ct := rr.Header().Get("Content-Type"); ct != "application/problem+json" {
+		t.Fatalf("Content-Type=%q", ct)
+	}
+	var doc map[string]any
+	if err := json.Unmarshal(rr.Body.Bytes(), &doc); err != nil {
+		t.Fatalf("decode problem: %v", err)
+	}
+	if doc["messageId"] != "server.generic.429" {
+		t.Fatalf("messageId=%v, want server.generic.429", doc["messageId"])
+	}
+}
diff --git a/api/internal/auth/sessions.go b/api/internal/auth/sessions.go
index 566f822b4..875a65e6b 100644
--- a/api/internal/auth/sessions.go
+++ b/api/internal/auth/sessions.go
@@ -12,6 +12,8 @@ import (
 	"time"
 
 	"github.com/GameplanePanel/gameplane/api/internal/db"
+	"github.com/GameplanePanel/gameplane/api/internal/httperr"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 )
 
 const (
@@ -129,17 +131,17 @@ func (s *SessionStore) Authenticate(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
 		cookie, err := req.Cookie(sessionCookie)
 		if err != nil {
-			http.Error(w, "unauthenticated", http.StatusUnauthorized)
+			httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 			return
 		}
 		u, csrf, err := s.lookup(req.Context(), cookie.Value)
 		if err != nil {
-			http.Error(w, "unauthenticated", http.StatusUnauthorized)
+			httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 			return
 		}
 		if isMutating(req.Method) {
 			if req.Header.Get(csrfHeader) != csrf {
-				http.Error(w, "csrf mismatch", http.StatusForbidden)
+				httperr.WriteMessage(w, req, messages.New("server.auth.csrf_mismatch", nil))
 				return
 			}
 		}
diff --git a/api/internal/db/migrations/common/016_user_language.sql b/api/internal/db/migrations/common/016_user_language.sql
new file mode 100644
index 000000000..af34123ff
--- /dev/null
+++ b/api/internal/db/migrations/common/016_user_language.sql
@@ -0,0 +1,6 @@
+-- User language choice (spec 019). language is a BCP 47 tag from the shipped
+-- language packs, or NULL when the user has no saved choice and follows the
+-- instance default. The column is nullable with no default, so existing rows
+-- keep NULL and need no backfill. Portable SQL: runs unchanged on SQLite and
+-- PostgreSQL.
+ALTER TABLE user_preferences ADD COLUMN language TEXT;
diff --git a/api/internal/db/preferences.go b/api/internal/db/preferences.go
index b77c1c2f9..db0b0fe65 100644
--- a/api/internal/db/preferences.go
+++ b/api/internal/db/preferences.go
@@ -21,6 +21,7 @@ type UserPreferences struct {
 	CustomSurface    *string // nullable #RRGGBB hex
 	CustomCSSEnabled bool    // whether the custom CSS overlay is injected
 	CustomCSS        *string // nullable sanitized CSS text (max 32 KiB)
+	Language         *string // nullable BCP 47 tag; nil = no saved choice (follow the instance default)
 	UpdatedAt        string  // RFC3339 UTC, application-generated in Go
 }
 
@@ -42,12 +43,12 @@ func DefaultUserPreferences() UserPreferences {
 // created account).
 func (s *Store) GetPreferences(ctx context.Context, userID int64) (UserPreferences, error) {
 	var p UserPreferences
-	var accent, surface, css sql.NullString
+	var accent, surface, css, language sql.NullString
 	var cssEnabled int
 	err := s.DB.QueryRowContext(ctx,
-		`SELECT theme_type, preset_id, appearance_mode, custom_accent, custom_surface, custom_css_enabled, custom_css, updated_at
+		`SELECT theme_type, preset_id, appearance_mode, custom_accent, custom_surface, custom_css_enabled, custom_css, language, updated_at
 		   FROM user_preferences WHERE user_id = ?`, userID).
-		Scan(&p.ThemeType, &p.PresetID, &p.AppearanceMode, &accent, &surface, &cssEnabled, &css, &p.UpdatedAt)
+		Scan(&p.ThemeType, &p.PresetID, &p.AppearanceMode, &accent, &surface, &cssEnabled, &css, &language, &p.UpdatedAt)
 	if errors.Is(err, sql.ErrNoRows) {
 		return DefaultUserPreferences(), nil
 	}
@@ -64,6 +65,9 @@ func (s *Store) GetPreferences(ctx context.Context, userID int64) (UserPreferenc
 	if css.Valid {
 		p.CustomCSS = &css.String
 	}
+	if language.Valid {
+		p.Language = &language.String
+	}
 	p.UpdatedAt = NormalizeTimestamp(p.UpdatedAt)
 	return p, nil
 }
@@ -73,7 +77,9 @@ func (s *Store) GetPreferences(ctx context.Context, userID int64) (UserPreferenc
 // written verbatim, so a caller that wants FR-012 retention must carry the
 // previously stored custom fields into p (the handler does this by reading
 // GetPreferences first and applying only the fields present in the request).
-// Enum validation and CSS sanitization live in the handlers.
+// Enum validation and CSS sanitization live in the handlers. The language
+// column is not written here (SetLanguage owns it), so the stored language
+// survives an upsert; the returned value echoes the caller's p.Language.
 func (s *Store) UpsertPreferences(ctx context.Context, userID int64, p UserPreferences) (UserPreferences, error) {
 	p.UpdatedAt = time.Now().UTC().Format(time.RFC3339)
 	cssEnabled := 0
@@ -106,7 +112,8 @@ func (s *Store) UpsertPreferences(ctx context.Context, userID int64, p UserPrefe
 // settings (FR-012): custom_accent, custom_surface and custom_css are nulled,
 // the overlay is disabled and the base mode returns to "preset". presetID
 // and appearanceMode are applied as given — the handler validates the enums
-// and resolves "omit" to the user's current values before calling.
+// and resolves "omit" to the user's current values before calling. The
+// language choice is not a custom setting and is kept (SetLanguage owns it).
 func (s *Store) ResetPreferences(ctx context.Context, userID int64, presetID, appearanceMode string) (UserPreferences, error) {
 	p := UserPreferences{
 		ThemeType:      "preset",
@@ -134,6 +141,26 @@ func (s *Store) ResetPreferences(ctx context.Context, userID int64, presetID, ap
 	return p, nil
 }
 
+// SetLanguage stores the user's language choice. A nil language clears it
+// back to "no saved choice". A user with no preferences row gets one with the
+// default preferences; an existing row changes only its language and
+// updated_at, so the theme and custom styling are untouched.
+func (s *Store) SetLanguage(ctx context.Context, userID int64, language *string) error {
+	d := DefaultUserPreferences()
+	_, err := s.DB.ExecContext(ctx,
+		`INSERT INTO user_preferences
+		    (user_id, theme_type, preset_id, appearance_mode, custom_css_enabled, language, updated_at)
+		 VALUES (?, ?, ?, ?, 0, ?, ?)
+		 ON CONFLICT (user_id) DO UPDATE SET
+		    language = excluded.language,
+		    updated_at = excluded.updated_at`,
+		userID, d.ThemeType, d.PresetID, d.AppearanceMode, nullableString(language), d.UpdatedAt)
+	if err != nil {
+		return fmt.Errorf("set language: %w", err)
+	}
+	return nil
+}
+
 func nullableString(p *string) any {
 	if p == nil {
 		return nil
diff --git a/api/internal/db/preferences_test.go b/api/internal/db/preferences_test.go
index 82fb5bdfa..788ac4025 100644
--- a/api/internal/db/preferences_test.go
+++ b/api/internal/db/preferences_test.go
@@ -93,6 +93,12 @@ func TestUserThemePreferencesMigration(t *testing.T) {
 		t.Error("index idx_user_preferences_user missing after migration 011")
 	}
 
+	// Apply the remaining migrations so GetPreferences sees the columns
+	// later migrations add (016 adds language).
+	if err := s.Migrate(ctx); err != nil {
+		t.Fatalf("apply remaining migrations: %v", err)
+	}
+
 	// A user created after the migration has no row; GetPreferences must
 	// return the pink defaults.
 	post := insertTestUser(t, s, "post-migration")
@@ -379,3 +385,141 @@ func TestUserPreferences_ResetWithoutRow(t *testing.T) {
 		t.Errorf("stored = %+v, want pink with nil customs", stored)
 	}
 }
+
+// strPtr returns a pointer to s, for the nullable language field in tests.
+func strPtr(s string) *string { return &s }
+
+// TestUserPreferences_SetLanguageRoundTrip checks that SetLanguage stores a
+// tag that GetPreferences returns, and that a nil language clears it.
+func TestUserPreferences_SetLanguageRoundTrip(t *testing.T) {
+	s := newShareLinksStore(t)
+	ctx := context.Background()
+	userID := insertTestUser(t, s, "lang-roundtrip")
+
+	if err := s.SetLanguage(ctx, userID, strPtr("de")); err != nil {
+		t.Fatalf("set language: %v", err)
+	}
+	prefs, err := s.GetPreferences(ctx, userID)
+	if err != nil {
+		t.Fatalf("get: %v", err)
+	}
+	if prefs.Language == nil || *prefs.Language != "de" {
+		t.Fatalf("Language = %v, want de", prefs.Language)
+	}
+
+	if err := s.SetLanguage(ctx, userID, nil); err != nil {
+		t.Fatalf("clear language: %v", err)
+	}
+	prefs, err = s.GetPreferences(ctx, userID)
+	if err != nil {
+		t.Fatalf("get after clear: %v", err)
+	}
+	if prefs.Language != nil {
+		t.Fatalf("Language = %q after clear, want nil", *prefs.Language)
+	}
+}
+
+// TestUserPreferences_UpsertKeepsLanguage checks that a theme save does not
+// touch the saved language, and that the returned value echoes the caller's
+// Language (the handler passes in the stored row it read first).
+func TestUserPreferences_UpsertKeepsLanguage(t *testing.T) {
+	s := newShareLinksStore(t)
+	ctx := context.Background()
+	userID := insertTestUser(t, s, "lang-upsert")
+
+	if err := s.SetLanguage(ctx, userID, strPtr("fr")); err != nil {
+		t.Fatalf("set language: %v", err)
+	}
+	stored, err := s.GetPreferences(ctx, userID)
+	if err != nil {
+		t.Fatalf("get: %v", err)
+	}
+	stored.AppearanceMode = "dark"
+	saved, err := s.UpsertPreferences(ctx, userID, stored)
+	if err != nil {
+		t.Fatalf("upsert: %v", err)
+	}
+	if saved.Language == nil || *saved.Language != "fr" {
+		t.Fatalf("returned Language = %v, want fr", saved.Language)
+	}
+
+	prefs, err := s.GetPreferences(ctx, userID)
+	if err != nil {
+		t.Fatalf("get after upsert: %v", err)
+	}
+	if prefs.AppearanceMode != "dark" {
+		t.Fatalf("AppearanceMode = %q, want dark", prefs.AppearanceMode)
+	}
+	if prefs.Language == nil || *prefs.Language != "fr" {
+		t.Fatalf("stored Language = %v after upsert, want fr", prefs.Language)
+	}
+}
+
+// TestUserPreferences_UpsertNewRowLanguageNil checks that an upsert creating a
+// new row leaves the language NULL.
+func TestUserPreferences_UpsertNewRowLanguageNil(t *testing.T) {
+	s := newShareLinksStore(t)
+	ctx := context.Background()
+	userID := insertTestUser(t, s, "lang-upsert-new")
+
+	if _, err := s.UpsertPreferences(ctx, userID, DefaultUserPreferences()); err != nil {
+		t.Fatalf("upsert: %v", err)
+	}
+	prefs, err := s.GetPreferences(ctx, userID)
+	if err != nil {
+		t.Fatalf("get: %v", err)
+	}
+	if prefs.Language != nil {
+		t.Fatalf("new row Language = %q, want nil", *prefs.Language)
+	}
+}
+
+// TestUserPreferences_ResetKeepsLanguage checks that a reset clears the custom
+// styling but keeps the saved language.
+func TestUserPreferences_ResetKeepsLanguage(t *testing.T) {
+	s := newShareLinksStore(t)
+	ctx := context.Background()
+	userID := insertTestUser(t, s, "lang-reset")
+
+	if err := s.SetLanguage(ctx, userID, strPtr("ja")); err != nil {
+		t.Fatalf("set language: %v", err)
+	}
+	if _, err := s.ResetPreferences(ctx, userID, "legacy", "light"); err != nil {
+		t.Fatalf("reset: %v", err)
+	}
+	prefs, err := s.GetPreferences(ctx, userID)
+	if err != nil {
+		t.Fatalf("get: %v", err)
+	}
+	if prefs.PresetID != "legacy" || prefs.AppearanceMode != "light" {
+		t.Fatalf("reset not applied: %+v", prefs)
+	}
+	if prefs.Language == nil || *prefs.Language != "ja" {
+		t.Fatalf("Language = %v after reset, want ja", prefs.Language)
+	}
+}
+
+// TestUserPreferences_SetLanguageNoRowGetsDefaults checks that SetLanguage
+// for a user with no preferences row inserts one with the default values.
+func TestUserPreferences_SetLanguageNoRowGetsDefaults(t *testing.T) {
+	s := newShareLinksStore(t)
+	ctx := context.Background()
+	userID := insertTestUser(t, s, "lang-no-row")
+
+	if err := s.SetLanguage(ctx, userID, strPtr("en")); err != nil {
+		t.Fatalf("set language: %v", err)
+	}
+	prefs, err := s.GetPreferences(ctx, userID)
+	if err != nil {
+		t.Fatalf("get: %v", err)
+	}
+	if prefs.ThemeType != "preset" || prefs.PresetID != "pink" || prefs.AppearanceMode != "system" {
+		t.Fatalf("defaults not applied: %+v", prefs)
+	}
+	if prefs.CustomCSSEnabled || prefs.CustomAccent != nil || prefs.CustomSurface != nil || prefs.CustomCSS != nil {
+		t.Fatalf("customs must stay at defaults: %+v", prefs)
+	}
+	if prefs.Language == nil || *prefs.Language != "en" {
+		t.Fatalf("Language = %v, want en", prefs.Language)
+	}
+}
diff --git a/api/internal/handlers/auth_provider_secret.go b/api/internal/handlers/auth_provider_secret.go
index d8b2377fe..69ae0d9d3 100644
--- a/api/internal/handlers/auth_provider_secret.go
+++ b/api/internal/handlers/auth_provider_secret.go
@@ -11,6 +11,7 @@ import (
 	"github.com/GameplanePanel/gameplane/api/internal/auth"
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 )
 
 // authProviderPrefix mirrors the registry's default configRef naming
@@ -54,17 +55,17 @@ func (h authProviderSecretHandler) put(w http.ResponseWriter, req *http.Request)
 		ClientSecret string `json:"clientSecret"`
 	}
 	if err := json.NewDecoder(req.Body).Decode(&body); err != nil {
-		http.Error(w, "invalid json", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.common.invalid_json", nil))
 		return
 	}
 	if body.ClientSecret == "" {
-		http.Error(w, "clientSecret is required", http.StatusUnprocessableEntity)
+		httperr.WriteMessage(w, req, messages.New("server.auth_providers.client_secret_required", nil))
 		return
 	}
 	data := map[string]string{"clientSecret": body.ClientSecret}
 	if err := upsertLabelledSecret(req.Context(), h.k, h.ns, secretName, auth.ProviderSecretLabel, data); err != nil {
 		if errors.Is(err, errNotManagedSecret) {
-			http.Error(w, err.Error(), http.StatusConflict)
+			httperr.WriteCode(w, req, http.StatusConflict, err)
 			return
 		}
 		httperr.Write(w, req, err)
diff --git a/api/internal/handlers/auth_providers.go b/api/internal/handlers/auth_providers.go
index 622a4a635..0892a3357 100644
--- a/api/internal/handlers/auth_providers.go
+++ b/api/internal/handlers/auth_providers.go
@@ -1,9 +1,13 @@
 package handlers
 
 import (
+	"encoding/json"
+	"log/slog"
 	"net/http"
 
 	"github.com/GameplanePanel/gameplane/api/internal/auth"
+	"github.com/GameplanePanel/gameplane/api/internal/db"
+	"github.com/GameplanePanel/gameplane/i18n/catalog"
 )
 
 type loginProvider struct {
@@ -39,3 +43,47 @@ func AuthProvidersHandler(reg *auth.Registry) http.HandlerFunc {
 		writeJSON(w, resp)
 	}
 }
+
+// fallbackLanguage is the tag served when no usable instance default is
+// stored. English is always shipped and complete.
+const fallbackLanguage = "en"
+
+// authLocaleResp is the GET /auth/locale body. It carries only the default
+// language tag: login privacy allows nothing else on an unauthenticated route.
+type authLocaleResp struct {
+	DefaultLanguage string `json:"defaultLanguage"`
+}
+
+// AuthLocaleHandler serves GET /auth/locale, a public, pre-auth endpoint that
+// tells the login page which language to show before anyone signs in. It
+// reads the admin's i18n config section. An absent, unparsable or unlisted
+// tag, or a database failure, all fall back to English; internal error text
+// is logged and never returned.
+func AuthLocaleHandler(store *db.Store) http.HandlerFunc {
+	return func(w http.ResponseWriter, req *http.Request) {
+		writeJSON(w, authLocaleResp{DefaultLanguage: instanceDefaultLanguage(req, store)})
+	}
+}
+
+// instanceDefaultLanguage resolves the stored i18n default to a listed tag.
+func instanceDefaultLanguage(req *http.Request, store *db.Store) string {
+	raw, ok, err := store.ConfigValue(req.Context(), "i18n")
+	if err != nil {
+		slog.Warn("auth locale: read i18n config", "err", err)
+		return fallbackLanguage
+	}
+	if !ok {
+		return fallbackLanguage
+	}
+	var section struct {
+		DefaultLanguage string `json:"defaultLanguage"`
+	}
+	if err := json.Unmarshal([]byte(raw), &section); err != nil {
+		slog.Warn("auth locale: parse i18n config", "err", err)
+		return fallbackLanguage
+	}
+	if section.DefaultLanguage == "" || !catalog.IsListed(section.DefaultLanguage) {
+		return fallbackLanguage
+	}
+	return section.DefaultLanguage
+}
diff --git a/api/internal/handlers/auth_providers_test.go b/api/internal/handlers/auth_providers_test.go
index 3ac6568b3..f5a8939a9 100644
--- a/api/internal/handlers/auth_providers_test.go
+++ b/api/internal/handlers/auth_providers_test.go
@@ -107,3 +107,74 @@ func TestAuthProviders_LabelFallsBackToName(t *testing.T) {
 		}
 	}
 }
+
+// seedI18nConfig stores the i18n config section as the admin config handler
+// would, with the raw JSON value given.
+func seedI18nConfig(t *testing.T, store *db.Store, blob string) {
+	t.Helper()
+	if _, err := store.DB.ExecContext(context.Background(),
+		`INSERT INTO config(key, value, updated_at) VALUES ('i18n', ?, datetime('now'))
+		 ON CONFLICT(key) DO UPDATE SET value = excluded.value`, blob); err != nil {
+		t.Fatalf("seed i18n config: %v", err)
+	}
+}
+
+func getLocale(t *testing.T, store *db.Store) (map[string]any, string) {
+	t.Helper()
+	rr := httptest.NewRecorder()
+	AuthLocaleHandler(store)(rr, httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/auth/locale", nil))
+	if rr.Code != http.StatusOK {
+		t.Fatalf("status = %d, body=%s", rr.Code, rr.Body.String())
+	}
+	var resp map[string]any
+	if err := json.Unmarshal(rr.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	return resp, rr.Body.String()
+}
+
+func TestAuthLocale_AbsentIsEnglish(t *testing.T) {
+	resp, _ := getLocale(t, newTestStore(t))
+	if resp["defaultLanguage"] != "en" {
+		t.Fatalf("defaultLanguage = %v, want en", resp["defaultLanguage"])
+	}
+}
+
+func TestAuthLocale_StoredEnglish(t *testing.T) {
+	store := newTestStore(t)
+	seedI18nConfig(t, store, `{"defaultLanguage":"en"}`)
+	resp, _ := getLocale(t, store)
+	if resp["defaultLanguage"] != "en" {
+		t.Fatalf("defaultLanguage = %v, want en", resp["defaultLanguage"])
+	}
+}
+
+func TestAuthLocale_UnlistedFallsBackToEnglish(t *testing.T) {
+	store := newTestStore(t)
+	seedI18nConfig(t, store, `{"defaultLanguage":"xx"}`)
+	resp, _ := getLocale(t, store)
+	if resp["defaultLanguage"] != "en" {
+		t.Fatalf("defaultLanguage = %v, want en for an unlisted tag", resp["defaultLanguage"])
+	}
+}
+
+func TestAuthLocale_UnparsableFallsBackToEnglish(t *testing.T) {
+	store := newTestStore(t)
+	seedI18nConfig(t, store, `not json`)
+	resp, _ := getLocale(t, store)
+	if resp["defaultLanguage"] != "en" {
+		t.Fatalf("defaultLanguage = %v, want en for unparsable config", resp["defaultLanguage"])
+	}
+}
+
+func TestAuthLocale_ResponseHasExactlyOneKey(t *testing.T) {
+	store := newTestStore(t)
+	seedI18nConfig(t, store, `{"defaultLanguage":"en"}`)
+	resp, raw := getLocale(t, store)
+	if len(resp) != 1 {
+		t.Fatalf("keys = %d, want exactly one; body=%s", len(resp), raw)
+	}
+	if _, ok := resp["defaultLanguage"]; !ok {
+		t.Fatalf("missing defaultLanguage key; body=%s", raw)
+	}
+}
diff --git a/api/internal/handlers/clusters.go b/api/internal/handlers/clusters.go
index 26896ac4c..515d39589 100644
--- a/api/internal/handlers/clusters.go
+++ b/api/internal/handlers/clusters.go
@@ -23,6 +23,7 @@ import (
 	"github.com/GameplanePanel/gameplane/api/internal/auth"
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 )
 
 // MountClusters wires /clusters onto the supplied router.
@@ -98,7 +99,7 @@ type clustersListResp struct {
 func (h clustersHandler) list(w http.ResponseWriter, req *http.Request) {
 	u := auth.UserFromContext(req.Context())
 	if u == nil {
-		http.Error(w, "unauthenticated", http.StatusUnauthorized)
+		httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 		return
 	}
 	out := clustersListResp{Items: make([]clusterRegistryView, 0)}
diff --git a/api/internal/handlers/config.go b/api/internal/handlers/config.go
index 975af88f2..6227ac6e2 100644
--- a/api/internal/handlers/config.go
+++ b/api/internal/handlers/config.go
@@ -19,6 +19,7 @@ import (
 	"github.com/GameplanePanel/gameplane/api/internal/auth"
 	"github.com/GameplanePanel/gameplane/api/internal/db"
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/notify"
 	"github.com/GameplanePanel/gameplane/api/internal/registry"
 	"github.com/GameplanePanel/gameplane/api/internal/telemetry"
@@ -116,21 +117,26 @@ func (h *configHandler) put(w http.ResponseWriter, req *http.Request) {
 	section := chi.URLParam(req, "section")
 	validate, ok := h.validators[section]
 	if !ok {
-		http.Error(w, "unknown section", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.config.unknown_section", nil))
 		return
 	}
 	body, err := io.ReadAll(req.Body)
 	if err != nil {
-		http.Error(w, "read body", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.config.read_body", nil))
 		return
 	}
 	if len(body) == 0 {
-		http.Error(w, "empty body", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.empty_body", nil))
 		return
 	}
 	canon, err := validate(body)
 	if err != nil {
-		http.Error(w, err.Error(), http.StatusUnprocessableEntity)
+		var m *httperr.Message
+		if errors.As(err, &m) {
+			httperr.WriteMessage(w, req, m)
+			return
+		}
+		httperr.WriteCode(w, req, http.StatusUnprocessableEntity, err)
 		return
 	}
 
@@ -148,7 +154,7 @@ func (h *configHandler) put(w http.ResponseWriter, req *http.Request) {
 		// transaction as the config write (see saveTelemetry).
 		if err := h.saveTelemetry(req.Context(), canon); err != nil {
 			if errors.Is(err, telemetry.ErrOperatorDisabled) {
-				http.Error(w, err.Error(), http.StatusConflict)
+				httperr.WriteCode(w, req, http.StatusConflict, err)
 				return
 			}
 			httperr.Write(w, req, err)
@@ -468,6 +474,7 @@ func newValidators(helmOIDCPresent bool) map[string]func([]byte) (json.RawMessag
 		"auth":                              validateAuth(helmOIDCPresent),
 		"notifications":                     validateNotifications,
 		"telemetry":                         validateTelemetry,
+		"i18n":                              validateI18n,
 		registry.ConfigSectionModRegistries: validateModRegistries,
 	}
 }
@@ -714,6 +721,7 @@ type notifSink struct {
 	Enabled   bool     `json:"enabled"`
 	ConfigRef string   `json:"configRef,omitempty"` // K8s Secret name holding the sink's credentials
 	Events    []string `json:"events,omitempty"`    // subset of notify.AllEvents; empty = notify.DefaultOn
+	Language  string   `json:"language,omitempty"`  // BCP 47 tag of a listed language; empty = instance default
 }
 
 type notifCfg struct {
@@ -739,6 +747,9 @@ func validateNotifications(body []byte) (json.RawMessage, error) {
 		if !validSinkKinds[s.Kind] {
 			return nil, fmt.Errorf("sinks[%d].kind must be one of discord|slack|smtp|webhook|ntfy", i)
 		}
+		if s.Language != "" && !languageListed(s.Language) {
+			return nil, messages.New("server.i18n.unknown_language", map[string]any{"language": s.Language})
+		}
 		// configRef stays optional so sink rows persisted before the
 		// delivery pipeline existed keep loading; the dispatcher skips
 		// enabled sinks without one and the UI flags them.
@@ -777,6 +788,31 @@ func validateTelemetry(body []byte) (json.RawMessage, error) {
 	return json.Marshal(c)
 }
 
+// i18nCfg is the instance language section: the default language for users
+// who have not chosen one, and the login page before sign-in.
+type i18nCfg struct {
+	DefaultLanguage string `json:"defaultLanguage"`
+}
+
+// validateI18n requires defaultLanguage to be a tag this release offers. An
+// unlisted tag returns a localizable *httperr.Message, so the save reports the
+// same error id to the dashboard in either language.
+func validateI18n(body []byte) (json.RawMessage, error) {
+	dec := json.NewDecoder(strings.NewReader(string(body)))
+	dec.DisallowUnknownFields()
+	var c i18nCfg
+	if err := dec.Decode(&c); err != nil {
+		return nil, fmt.Errorf("invalid json: %w", err)
+	}
+	if c.DefaultLanguage == "" {
+		return nil, fmt.Errorf("defaultLanguage is required")
+	}
+	if !languageListed(c.DefaultLanguage) {
+		return nil, messages.New("server.i18n.unlisted_language", map[string]any{"language": c.DefaultLanguage})
+	}
+	return json.Marshal(c)
+}
+
 // modRegistryEntry is one provider's admin-managed mod-registry
 // declaration: which provider, and (optionally) a non-default Secret name
 // holding its key. It carries no secret material — the value lives in a
diff --git a/api/internal/handlers/config_validators_test.go b/api/internal/handlers/config_validators_test.go
index 7a8e09e65..b199abb9b 100644
--- a/api/internal/handlers/config_validators_test.go
+++ b/api/internal/handlers/config_validators_test.go
@@ -1,8 +1,12 @@
 package handlers
 
 import (
+	"errors"
+	"net/http"
 	"strings"
 	"testing"
+
+	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 )
 
 // These tests pin the per-section validators directly so error branches
@@ -234,3 +238,48 @@ func TestUpdatesSectionRemoved(t *testing.T) {
 		}
 	}
 }
+
+func TestValidateI18n(t *testing.T) {
+	cases := []struct {
+		name string
+		in   string
+		ok   bool
+	}{
+		{"valid en", `{"defaultLanguage":"en"}`, true},
+		{"unknown key", `{"defaultLanguage":"en","extra":1}`, false},
+		{"missing field", `{}`, false},
+		{"empty tag", `{"defaultLanguage":""}`, false},
+		{"bad json", `not json`, false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			canon, err := validateI18n([]byte(tc.in))
+			if tc.ok && err != nil {
+				t.Fatalf("unexpected: %v", err)
+			}
+			if tc.ok && string(canon) != tc.in {
+				t.Fatalf("canonicalized output: got %s, want %s", canon, tc.in)
+			}
+			if !tc.ok && err == nil {
+				t.Fatal("want error, got nil")
+			}
+		})
+	}
+}
+
+func TestValidateI18n_UnlistedTagIsLocalizableMessage(t *testing.T) {
+	_, err := validateI18n([]byte(`{"defaultLanguage":"xx"}`))
+	var m *httperr.Message
+	if !errors.As(err, &m) {
+		t.Fatalf("err = %v (%T), want *httperr.Message", err, err)
+	}
+	if m.ID != "server.i18n.unlisted_language" {
+		t.Fatalf("ID = %q, want server.i18n.unlisted_language", m.ID)
+	}
+	if m.Status != http.StatusBadRequest {
+		t.Fatalf("Status = %d, want 400", m.Status)
+	}
+	if m.Args["language"] != "xx" {
+		t.Fatalf("args.language = %v, want xx", m.Args["language"])
+	}
+}
diff --git a/api/internal/handlers/fleet.go b/api/internal/handlers/fleet.go
index ee87779b9..e043b1569 100644
--- a/api/internal/handlers/fleet.go
+++ b/api/internal/handlers/fleet.go
@@ -20,6 +20,7 @@ import (
 	"github.com/GameplanePanel/gameplane/api/internal/db"
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/rbac"
 	"github.com/GameplanePanel/gameplane/api/internal/scope"
 )
@@ -359,7 +360,7 @@ func (h fleetHandler) resources(kind string) http.HandlerFunc {
 func (h fleetHandler) start(w http.ResponseWriter, req *http.Request) (*auth.User, fleetFilter, bool) {
 	u := auth.UserFromContext(req.Context())
 	if u == nil {
-		http.Error(w, "unauthenticated", http.StatusUnauthorized)
+		httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 		return nil, fleetFilter{}, false
 	}
 	f, err := parseFleetFilter(req)
@@ -611,7 +612,7 @@ func (h fleetHandler) readInventory(ctx context.Context, c fleetCluster) (*fleet
 func (h fleetHandler) serverAccess(w http.ResponseWriter, req *http.Request) {
 	u := auth.UserFromContext(req.Context())
 	if u == nil {
-		http.Error(w, "unauthenticated", http.StatusUnauthorized)
+		httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 		return
 	}
 	k, ok := resolveCluster(w, req, h.reg)
@@ -631,7 +632,7 @@ func (h fleetHandler) serverAccess(w http.ResponseWriter, req *http.Request) {
 	}
 	access := serverFleetAccess(u, cl, ns, obj)
 	if !u.Can("servers:read", true, cl, ns) && !access.IsOwner && !access.IsCollaborator {
-		http.Error(w, "forbidden", http.StatusForbidden)
+		httperr.WriteMessage(w, req, messages.New("server.forbidden", nil))
 		return
 	}
 	writeJSON(w, struct {
diff --git a/api/internal/handlers/lifecycle.go b/api/internal/handlers/lifecycle.go
index 2091ad9dd..5d10e517a 100644
--- a/api/internal/handlers/lifecycle.go
+++ b/api/internal/handlers/lifecycle.go
@@ -13,6 +13,7 @@ import (
 
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/scope"
 )
 
@@ -70,11 +71,11 @@ func wipeDataHandler(reg *kube.Registry) http.HandlerFunc {
 		}
 		var body wipeDataReq
 		if err := json.NewDecoder(io.LimitReader(req.Body, 1<<16)).Decode(&body); err != nil {
-			http.Error(w, "bad request", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.bad_request", nil))
 			return
 		}
 		if body.Confirm != name {
-			http.Error(w, "confirmation does not match server name", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.lifecycle.confirmation_mismatch", nil))
 			return
 		}
 		token := strconv.FormatInt(time.Now().UTC().UnixNano(), 10)
@@ -205,7 +206,7 @@ func cloneHandler(reg *kube.Registry) http.HandlerFunc {
 		}
 		var body cloneReq
 		if err := json.NewDecoder(io.LimitReader(req.Body, 1<<16)).Decode(&body); err != nil || body.NewName == "" {
-			http.Error(w, "newName required", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.lifecycle.new_name_required", nil))
 			return
 		}
 		src, ok := authorizedServer(w, req, k, ns, name)
diff --git a/api/internal/handlers/module_upload.go b/api/internal/handlers/module_upload.go
index 2abc334cc..442943fb7 100644
--- a/api/internal/handlers/module_upload.go
+++ b/api/internal/handlers/module_upload.go
@@ -4,7 +4,7 @@
 //   - DELETE /modules/sources/{name}/upload/{module}   — remove a bundle
 //
 // The body is a tar.gz or zip holding one module directory (module.yaml
-// + template.yaml [+ README.md, icon.png]). After validation the files
+// + template.yaml [+ README.md, icon.png, locales/<tag>.json]). After validation the files
 // are written into a ConfigMap labeled gameplane.local/module-upload=true in
 // the operator namespace — the exact shape an upload-type ModuleSource
 // indexes, and the same thing `kubectl apply` of such a ConfigMap
@@ -34,6 +34,7 @@ import (
 
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/i18n/pack"
 )
 
 // Bundle files are a couple of YAML docs and an icon; the ConfigMap
@@ -60,9 +61,16 @@ const (
 
 // bundleFileNames are the canonical files copied into the ConfigMap;
 // anything else in the archive (junk like .DS_Store, nested docs) is
-// ignored.
+// ignored. Translation files locales/<tag>.json are copied too, under the
+// ConfigMap key locales.<tag>.json (a key cannot contain "/").
 var bundleFileNames = []string{"module.yaml", "template.yaml", "README.md", "icon.png"}
 
+const (
+	uploadLocalesDir       = "locales"
+	uploadLocaleKeyPrefix  = "locales."
+	uploadLocaleFileSuffix = ".json"
+)
+
 // uploadedMetadata is the subset of module.yaml the API validates and
 // echoes back for the dashboard's preview.
 type uploadedMetadata struct {
@@ -259,6 +267,14 @@ func parseUploadedBundle(body []byte) (map[string][]byte, *uploadedMetadata, err
 			total += len(data)
 		}
 	}
+	localeFiles, err := uploadedLocaleFiles(extracted, dir)
+	if err != nil {
+		return nil, nil, err
+	}
+	for key, data := range localeFiles {
+		files[key] = data
+		total += len(data)
+	}
 	if total > maxUploadBundleBytes {
 		return nil, nil, fmt.Errorf("bundle files exceed the %d KiB limit", maxUploadBundleBytes>>10)
 	}
@@ -297,6 +313,38 @@ func parseUploadedBundle(body []byte) (map[string][]byte, *uploadedMetadata, err
 	return files, &meta, nil
 }
 
+// uploadedLocaleFiles collects the locales/<tag>.json members of the module
+// directory dir as ConfigMap keys ("locales.<tag>.json"). The English
+// reference en.json is never shipped, non-JSON members are ignored, and a file
+// name that is not a valid language tag rejects the upload. Size is not capped
+// here: the caller counts these bytes against the bundle limit, so an oversized
+// upload is refused loudly instead of losing a language.
+func uploadedLocaleFiles(extracted map[string][]byte, dir string) (map[string][]byte, error) {
+	prefix := uploadLocalesDir + "/"
+	if dir != "." {
+		prefix = dir + "/" + prefix
+	}
+	out := map[string][]byte{}
+	for key, data := range extracted {
+		if !strings.HasPrefix(key, prefix) {
+			continue
+		}
+		name := strings.TrimPrefix(key, prefix)
+		if strings.Contains(name, "/") || !strings.HasSuffix(name, uploadLocaleFileSuffix) {
+			continue
+		}
+		tag := strings.TrimSuffix(name, uploadLocaleFileSuffix)
+		if tag == "en" {
+			continue
+		}
+		if !pack.ValidTag(tag) {
+			return nil, fmt.Errorf("locales/%s: %q is not a valid language tag", name, tag)
+		}
+		out[uploadLocaleKeyPrefix+tag+uploadLocaleFileSuffix] = data
+	}
+	return out, nil
+}
+
 var errUploadTooLarge = errors.New("archive expands past the decompression limit")
 
 // budgetReader wraps an io.Reader, counts bytes read, and returns an error
diff --git a/api/internal/handlers/module_upload_locales_test.go b/api/internal/handlers/module_upload_locales_test.go
new file mode 100644
index 000000000..28d8b1995
--- /dev/null
+++ b/api/internal/handlers/module_upload_locales_test.go
@@ -0,0 +1,71 @@
+package handlers
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestParseUploadedBundle_CarriesLocales(t *testing.T) {
+	t.Parallel()
+	files := validBundleFiles()
+	files["factorio/locales/fr.json"] = `{"template.displayName":{"defaultMessage":"Usine"}}`
+	files["factorio/locales/pt-BR.json"] = `{}`
+	files["factorio/locales/en.json"] = `{}`
+	files["factorio/locales/notes.txt"] = `ignored`
+	files["factorio/locales/sub/x.json"] = `{}`
+
+	got, _, err := parseUploadedBundle(bundleTarGz(t, files))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(got["locales.fr.json"]) != files["factorio/locales/fr.json"] || got["locales.pt-BR.json"] == nil {
+		t.Fatalf("keys = %v", localeKeys(got))
+	}
+	for _, key := range []string{"locales.en.json", "locales.notes.json", "locales.x.json", "locales/fr.json"} {
+		if _, ok := got[key]; ok {
+			t.Errorf("unexpected key %q", key)
+		}
+	}
+}
+
+func TestParseUploadedBundle_LocalesInFlatArchive(t *testing.T) {
+	t.Parallel()
+	flat := map[string]string{}
+	for name, body := range validBundleFiles() {
+		flat[strings.TrimPrefix(name, "factorio/")] = body
+	}
+	flat["locales/fr.json"] = `{}`
+	got, _, err := parseUploadedBundle(bundleTarGz(t, flat))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got["locales.fr.json"] == nil {
+		t.Fatalf("keys = %v", localeKeys(got))
+	}
+}
+
+func TestParseUploadedBundle_RejectsInvalidLocaleTag(t *testing.T) {
+	t.Parallel()
+	files := validBundleFiles()
+	files["factorio/locales/xx_YY.json"] = `{}`
+	if _, _, err := parseUploadedBundle(bundleTarGz(t, files)); err == nil {
+		t.Fatal("invalid language tag accepted")
+	}
+}
+
+func TestParseUploadedBundle_LocalesCountTowardLimit(t *testing.T) {
+	t.Parallel()
+	files := validBundleFiles()
+	files["factorio/locales/fr.json"] = strings.Repeat("a", maxUploadBundleBytes)
+	if _, _, err := parseUploadedBundle(bundleTarGz(t, files)); err == nil {
+		t.Fatal("over-limit locale file accepted")
+	}
+}
+
+func localeKeys(m map[string][]byte) []string {
+	out := make([]string, 0, len(m))
+	for k := range m {
+		out = append(out, k)
+	}
+	return out
+}
diff --git a/api/internal/handlers/modules.go b/api/internal/handlers/modules.go
index cf06536f1..b602a204c 100644
--- a/api/internal/handlers/modules.go
+++ b/api/internal/handlers/modules.go
@@ -5,6 +5,7 @@
 //                                         across sources, with installation state
 //   - GET    /modules                   — list installed Module CRs
 //   - POST   /modules                   — install: create a Module CR
+//   - GET    /modules/{name}/locales/{tag} — module translations for a language
 //   - PATCH  /modules/{name}            — upgrade: patch spec.version
 //   - DELETE /modules/{name}            — uninstall: delete the Module CR
 //
@@ -52,6 +53,7 @@ func MountModules(r chi.Router, k *kube.Client, namespace string) {
 			r.Post("/preview", h.builderPreview)
 			r.Post("/export", h.builderExport)
 		})
+		r.Get("/{name}/locales/{tag}", h.getLocales)
 		r.Get("/{name}", h.getInstalled)
 		r.Patch("/{name}", h.upgrade)
 		r.Delete("/{name}", h.uninstall)
diff --git a/api/internal/handlers/modules_locales.go b/api/internal/handlers/modules_locales.go
new file mode 100644
index 000000000..a81851202
--- /dev/null
+++ b/api/internal/handlers/modules_locales.go
@@ -0,0 +1,73 @@
+package handlers
+
+import (
+	"net/http"
+
+	"github.com/go-chi/chi/v5"
+	"golang.org/x/text/language"
+	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+
+	"github.com/GameplanePanel/gameplane/api/internal/httperr"
+	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+)
+
+// localesConfigMapSuffix names the ConfigMap the operator writes a module's
+// validated translations to: <module name> + this suffix, in the operator
+// namespace. Keys are "<tag>.json" holding an app.json style entry map.
+const localesConfigMapSuffix = "-locales"
+
+// getLocales serves GET /modules/{name}/locales/{tag}: the module's
+// translated messages for the language as a flat id -> message map. The tag
+// falls back to its base language; an unknown or malformed tag, a module
+// without translations, and a missing ConfigMap all yield an empty object.
+// Only a missing Module is a 404.
+func (h modulesHandler) getLocales(w http.ResponseWriter, req *http.Request) {
+	name, tag := chi.URLParam(req, "name"), chi.URLParam(req, "tag")
+	ctx := req.Context()
+	if _, err := h.k.Dynamic.Resource(kube.GVRModule).Get(ctx, name, metav1.GetOptions{}); err != nil {
+		httperr.Write(w, req, err)
+		return
+	}
+	cm, err := h.k.Typed.CoreV1().ConfigMaps(h.namespace).Get(ctx, name+localesConfigMapSuffix, metav1.GetOptions{})
+	if apierrors.IsNotFound(err) {
+		writeJSON(w, map[string]string{})
+		return
+	}
+	if err != nil {
+		httperr.Write(w, req, err)
+		return
+	}
+	writeJSON(w, resolveLocale(cm.Data, tag))
+}
+
+// resolveLocale picks the translation for tag from the ConfigMap data (keys
+// "<tag>.json"), trying the full tag and then its base language. It returns
+// an empty map when nothing usable matches.
+func resolveLocale(data map[string]string, tag string) map[string]string {
+	out := map[string]string{}
+	parsed, err := language.Parse(tag)
+	if err != nil {
+		return out
+	}
+	candidates := []string{parsed.String()}
+	if base, _ := parsed.Base(); base.String() != candidates[0] && base.String() != "und" {
+		candidates = append(candidates, base.String())
+	}
+	for _, c := range candidates {
+		raw, ok := data[c+".json"]
+		if !ok {
+			continue
+		}
+		entries, err := pack.ParseEntries([]byte(raw))
+		if err != nil {
+			continue
+		}
+		for id, e := range entries {
+			out[id] = e.DefaultMessage
+		}
+		return out
+	}
+	return out
+}
diff --git a/api/internal/handlers/modules_locales_test.go b/api/internal/handlers/modules_locales_test.go
new file mode 100644
index 000000000..44d4a0296
--- /dev/null
+++ b/api/internal/handlers/modules_locales_test.go
@@ -0,0 +1,173 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/url"
+	"strings"
+	"testing"
+
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+const (
+	frJSON = `{"template.displayName":{"defaultMessage":"Jeu"},"module.summary":{"defaultMessage":"Résumé","description":"d"}}`
+	ptJSON = `{"template.displayName":{"defaultMessage":"Jogo"}}`
+)
+
+func localesFixture(t *testing.T, data map[string]string) http.Handler {
+	t.Helper()
+	k := fakeKubeClient(newModule("mc", map[string]any{"name": "minecraft"}))
+	if data != nil {
+		if _, err := k.Typed.CoreV1().ConfigMaps("gameplane-system").Create(t.Context(), &corev1.ConfigMap{
+			ObjectMeta: metav1.ObjectMeta{Name: "mc-locales", Namespace: "gameplane-system"},
+			Data:       data,
+		}, metav1.CreateOptions{}); err != nil {
+			t.Fatal(err)
+		}
+	}
+	return mountModulesRouter(k)
+}
+
+func decodeLocales(t *testing.T, body []byte) map[string]string {
+	t.Helper()
+	var out map[string]string
+	if err := json.Unmarshal(body, &out); err != nil {
+		t.Fatalf("decode %q: %v", body, err)
+	}
+	return out
+}
+
+func TestGetLocales_TagHit(t *testing.T) {
+	h := localesFixture(t, map[string]string{"fr.json": frJSON, "pt.json": ptJSON})
+	rr := do(t, h, "GET", "/modules/mc/locales/fr", nil)
+	if rr.Code != http.StatusOK {
+		t.Fatalf("status = %d: %s", rr.Code, rr.Body)
+	}
+	got := decodeLocales(t, rr.Body.Bytes())
+	if len(got) != 2 || got["template.displayName"] != "Jeu" || got["module.summary"] != "Résumé" {
+		t.Errorf("body = %v", got)
+	}
+}
+
+func TestGetLocales_FallsBackToBaseLanguage(t *testing.T) {
+	h := localesFixture(t, map[string]string{"fr.json": frJSON, "pt.json": ptJSON})
+	rr := do(t, h, "GET", "/modules/mc/locales/pt-BR", nil)
+	if got := decodeLocales(t, rr.Body.Bytes()); got["template.displayName"] != "Jogo" {
+		t.Errorf("body = %v", got)
+	}
+}
+
+func TestGetLocales_RegionalPackWinsOverBase(t *testing.T) {
+	h := localesFixture(t, map[string]string{
+		"pt.json":    ptJSON,
+		"pt-BR.json": `{"template.displayName":{"defaultMessage":"Jogo BR"}}`,
+	})
+	rr := do(t, h, "GET", "/modules/mc/locales/pt-BR", nil)
+	if got := decodeLocales(t, rr.Body.Bytes()); got["template.displayName"] != "Jogo BR" {
+		t.Errorf("body = %v", got)
+	}
+}
+
+func TestGetLocales_UnknownAndInvalidTagsAreEmpty(t *testing.T) {
+	h := localesFixture(t, map[string]string{"fr.json": frJSON})
+	for _, tag := range []string{"de", "not a tag!", "x"} {
+		rr := do(t, h, "GET", "/modules/mc/locales/"+url.PathEscape(tag), nil)
+		if rr.Code != http.StatusOK {
+			t.Errorf("tag %q: status = %d", tag, rr.Code)
+			continue
+		}
+		if got := decodeLocales(t, rr.Body.Bytes()); len(got) != 0 {
+			t.Errorf("tag %q: body = %v", tag, got)
+		}
+	}
+}
+
+func TestGetLocales_NoConfigMapIsEmpty(t *testing.T) {
+	h := localesFixture(t, nil)
+	rr := do(t, h, "GET", "/modules/mc/locales/fr", nil)
+	if rr.Code != http.StatusOK {
+		t.Fatalf("status = %d", rr.Code)
+	}
+	if got := decodeLocales(t, rr.Body.Bytes()); len(got) != 0 {
+		t.Errorf("body = %v", got)
+	}
+}
+
+func TestGetLocales_MissingModuleIs404(t *testing.T) {
+	h := localesFixture(t, map[string]string{"fr.json": frJSON})
+	if rr := do(t, h, "GET", "/modules/ghost/locales/fr", nil); rr.Code != http.StatusNotFound {
+		t.Errorf("status = %d, want 404", rr.Code)
+	}
+}
+
+func TestGetLocales_MalformedValueIsSkipped(t *testing.T) {
+	h := localesFixture(t, map[string]string{"fr.json": `{not json`})
+	rr := do(t, h, "GET", "/modules/mc/locales/fr", nil)
+	if rr.Code != http.StatusOK {
+		t.Fatalf("status = %d", rr.Code)
+	}
+	if got := decodeLocales(t, rr.Body.Bytes()); len(got) != 0 {
+		t.Errorf("body = %v", got)
+	}
+}
+
+func TestGetLocales_MalformedRegionalFallsThroughToBase(t *testing.T) {
+	h := localesFixture(t, map[string]string{"pt-BR.json": `{bad`, "pt.json": ptJSON})
+	rr := do(t, h, "GET", "/modules/mc/locales/pt-BR", nil)
+	if got := decodeLocales(t, rr.Body.Bytes()); got["template.displayName"] != "Jogo" {
+		t.Errorf("body = %v", got)
+	}
+}
+
+func TestResolveLocale(t *testing.T) {
+	data := map[string]string{"zh-Hans.json": `{"a":{"defaultMessage":"简"}}`, "zh.json": `{"a":{"defaultMessage":"中"}}`}
+	cases := []struct {
+		tag, want string
+	}{
+		{"zh-Hans", "简"},
+		{"zh-Hans-CN", "中"},
+		{"zh", "中"},
+		{"zh-TW", "中"},
+		{"en", ""},
+		{"", ""},
+	}
+	for _, c := range cases {
+		if got := resolveLocale(data, c.tag)["a"]; got != c.want {
+			t.Errorf("resolveLocale(%q) = %q, want %q", c.tag, got, c.want)
+		}
+	}
+	if got := resolveLocale(nil, "fr"); got == nil || len(got) != 0 {
+		t.Errorf("nil data = %v", got)
+	}
+}
+
+func TestGetLocales_MalformedTagsAreEmptyJSON(t *testing.T) {
+	h := localesFixture(t, map[string]string{"fr.json": frJSON})
+	for _, tag := range []string{"a%00b", strings.Repeat("a", 200), "en-XA-"} {
+		rr := do(t, h, "GET", "/modules/mc/locales/"+tag, nil)
+		if rr.Code != http.StatusOK {
+			t.Errorf("tag %q: status = %d", tag, rr.Code)
+			continue
+		}
+		if got := decodeLocales(t, rr.Body.Bytes()); len(got) != 0 {
+			t.Errorf("tag %q: body = %v", tag, got)
+		}
+	}
+}
+
+func TestGetLocales_ReturnsICUStringsVerbatim(t *testing.T) {
+	const icu = "{count, plural, one {# item} other {# items}}"
+	h := localesFixture(t, map[string]string{"fr.json": `{"template.displayName":{"defaultMessage":"` + icu + `"}}`})
+	rr := do(t, h, "GET", "/modules/mc/locales/fr", nil)
+	if rr.Code != http.StatusOK {
+		t.Fatalf("status = %d", rr.Code)
+	}
+	if ct := rr.Header().Get("Content-Type"); !strings.HasPrefix(ct, "application/json") {
+		t.Errorf("Content-Type = %q", ct)
+	}
+	if got := decodeLocales(t, rr.Body.Bytes()); got["template.displayName"] != icu {
+		t.Errorf("body = %v", got)
+	}
+}
diff --git a/api/internal/handlers/notifications.go b/api/internal/handlers/notifications.go
index 55e414a3e..8b5ca9ef1 100644
--- a/api/internal/handlers/notifications.go
+++ b/api/internal/handlers/notifications.go
@@ -13,6 +13,7 @@ import (
 	"github.com/GameplanePanel/gameplane/api/internal/auth"
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/notify"
 )
 
@@ -37,9 +38,9 @@ func MountNotifications(r chi.Router, n *notify.Notifier, k *kube.Client, contro
 			case err == nil:
 				writeJSON(w, map[string]any{"delivered": true})
 			case errors.Is(err, notify.ErrUnknownSink):
-				http.Error(w, err.Error(), http.StatusNotFound)
+				httperr.WriteCode(w, req, http.StatusNotFound, err)
 			case errors.Is(err, notify.ErrSinkNotConfigured):
-				http.Error(w, err.Error(), http.StatusUnprocessableEntity)
+				httperr.WriteCode(w, req, http.StatusUnprocessableEntity, err)
 			default:
 				// Sink exists and is configured but delivery failed — relay
 				// the (URL-sanitized) cause so the admin can fix the endpoint
@@ -125,27 +126,27 @@ func sinkSecretData(b sinkSecretBody) (map[string]string, error) {
 func (h notificationsHandler) putSecret(w http.ResponseWriter, req *http.Request) {
 	name := chi.URLParam(req, "name")
 	if !dnsLabelRE.MatchString(name) {
-		http.Error(w, "sink name must be a DNS label (lowercase, digits, hyphens)", http.StatusUnprocessableEntity)
+		httperr.WriteMessage(w, req, messages.New("server.notifications.sink_name_not_dns_label", nil))
 		return
 	}
 	secretName := sinkSecretPrefix + name
 	if len(secretName) > 63 {
-		http.Error(w, fmt.Sprintf("sink name too long: %q must fit a DNS label with the %q prefix", name, sinkSecretPrefix), http.StatusUnprocessableEntity)
+		httperr.WriteCode(w, req, http.StatusUnprocessableEntity, fmt.Errorf("sink name too long: %q must fit a DNS label with the %q prefix", name, sinkSecretPrefix))
 		return
 	}
 	var body sinkSecretBody
 	if err := json.NewDecoder(req.Body).Decode(&body); err != nil {
-		http.Error(w, "invalid json", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.common.invalid_json", nil))
 		return
 	}
 	data, err := sinkSecretData(body)
 	if err != nil {
-		http.Error(w, err.Error(), http.StatusUnprocessableEntity)
+		httperr.WriteCode(w, req, http.StatusUnprocessableEntity, err)
 		return
 	}
 	if err := upsertLabelledSecret(req.Context(), h.k, h.ns, secretName, notify.SinkSecretLabel, data); err != nil {
 		if errors.Is(err, errNotManagedSecret) {
-			http.Error(w, err.Error(), http.StatusConflict)
+			httperr.WriteCode(w, req, http.StatusConflict, err)
 			return
 		}
 		httperr.Write(w, req, err)
@@ -164,7 +165,7 @@ func (h notificationsHandler) putSecret(w http.ResponseWriter, req *http.Request
 func (h notificationsHandler) deleteSecret(w http.ResponseWriter, req *http.Request) {
 	name := chi.URLParam(req, "name")
 	if !dnsLabelRE.MatchString(name) {
-		http.Error(w, "sink name must be a DNS label (lowercase, digits, hyphens)", http.StatusUnprocessableEntity)
+		httperr.WriteMessage(w, req, messages.New("server.notifications.sink_name_not_dns_label", nil))
 		return
 	}
 	if err := deleteManagedSecret(req.Context(), h.k, h.ns, sinkSecretPrefix+name, notify.SinkSecretLabel); err != nil {
diff --git a/api/internal/handlers/notifications_language_test.go b/api/internal/handlers/notifications_language_test.go
new file mode 100644
index 000000000..7639b3827
--- /dev/null
+++ b/api/internal/handlers/notifications_language_test.go
@@ -0,0 +1,56 @@
+package handlers
+
+import (
+	"errors"
+	"strings"
+	"testing"
+
+	"github.com/GameplanePanel/gameplane/api/internal/httperr"
+)
+
+// overrideListed points languageListed at a fixed set of tags for one test.
+func overrideListed(t *testing.T, tags ...string) {
+	t.Helper()
+	prev := languageListed
+	languageListed = func(tag string) bool {
+		for _, want := range tags {
+			if tag == want {
+				return true
+			}
+		}
+		return false
+	}
+	t.Cleanup(func() { languageListed = prev })
+}
+
+func TestValidateNotifications_Language(t *testing.T) {
+	overrideListed(t, "en", "fr")
+
+	out, err := validateNotifications([]byte(`{"sinks":[{"name":"a","kind":"webhook","enabled":true,"language":"fr"}]}`))
+	if err != nil {
+		t.Fatalf("listed language: %v", err)
+	}
+	if !strings.Contains(string(out), `"language":"fr"`) {
+		t.Fatalf("canonical JSON dropped language: %s", out)
+	}
+
+	_, err = validateNotifications([]byte(`{"sinks":[{"name":"a","kind":"webhook","enabled":true,"language":"zz"}]}`))
+	var m *httperr.Message
+	if !errors.As(err, &m) {
+		t.Fatalf("unknown language: err = %v, want *httperr.Message", err)
+	}
+	if m.ID != "server.i18n.unknown_language" {
+		t.Fatalf("ID = %q", m.ID)
+	}
+	if m.Args["language"] != "zz" {
+		t.Fatalf("args.language = %v, want zz", m.Args["language"])
+	}
+
+	out, err = validateNotifications([]byte(`{"sinks":[{"name":"a","kind":"webhook","enabled":true}]}`))
+	if err != nil {
+		t.Fatalf("omitted language: %v", err)
+	}
+	if strings.Contains(string(out), `"language"`) {
+		t.Fatalf("omitted language emitted a key: %s", out)
+	}
+}
diff --git a/api/internal/handlers/ownership.go b/api/internal/handlers/ownership.go
index 2544fbe40..55d277261 100644
--- a/api/internal/handlers/ownership.go
+++ b/api/internal/handlers/ownership.go
@@ -20,6 +20,7 @@ import (
 	"github.com/GameplanePanel/gameplane/api/internal/db"
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/scope"
 )
 
@@ -63,7 +64,7 @@ func stampOwner(obj *unstructured.Unstructured, req *http.Request) {
 func requireOwnerOrAdmin(w http.ResponseWriter, req *http.Request, reg *kube.Registry, k *kube.Client, ns, name string) (*unstructured.Unstructured, bool) {
 	u := auth.UserFromContext(req.Context())
 	if u == nil {
-		http.Error(w, "unauthenticated", http.StatusUnauthorized)
+		httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 		return nil, false
 	}
 	cl, err := scope.ResolveCluster(req, reg)
@@ -76,7 +77,7 @@ func requireOwnerOrAdmin(w http.ResponseWriter, req *http.Request, reg *kube.Reg
 		return nil, false
 	}
 	if !u.Can("*", true, cl, ns) && !isServerOwner(obj, u.ID) {
-		http.Error(w, "forbidden", http.StatusForbidden)
+		httperr.WriteMessage(w, req, messages.New("server.forbidden", nil))
 		return nil, false
 	}
 	return obj, true
@@ -170,14 +171,14 @@ func (h *ownershipHandler) transfer(w http.ResponseWriter, req *http.Request) {
 	}
 	var body transferReq
 	if err := json.NewDecoder(io.LimitReader(req.Body, 1<<16)).Decode(&body); err != nil || body.UserID <= 0 {
-		http.Error(w, "userId required", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.ownership.user_id_required", nil))
 		return
 	}
 	var username string
 	err := h.db.DB.QueryRowContext(req.Context(),
 		`SELECT username FROM users WHERE id = ?`, body.UserID).Scan(&username)
 	if errors.Is(err, sql.ErrNoRows) {
-		http.Error(w, "user not found", http.StatusNotFound)
+		httperr.WriteMessage(w, req, messages.New("server.common.user_not_found", nil))
 		return
 	}
 	if err != nil {
@@ -220,7 +221,7 @@ func (h *ownershipHandler) setCollaborators(w http.ResponseWriter, req *http.Req
 	}
 	var body setCollaboratorsReq
 	if err := json.NewDecoder(io.LimitReader(req.Body, 1<<16)).Decode(&body); err != nil {
-		http.Error(w, "invalid request", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.ownership.invalid_request", nil))
 		return
 	}
 
@@ -238,7 +239,7 @@ func (h *ownershipHandler) setCollaborators(w http.ResponseWriter, req *http.Req
 		err := h.db.DB.QueryRowContext(req.Context(),
 			`SELECT id FROM users WHERE username = ?`, name).Scan(&id)
 		if errors.Is(err, sql.ErrNoRows) {
-			http.Error(w, "user not found: "+name, http.StatusBadRequest)
+			httperr.WriteCode(w, req, http.StatusBadRequest, errors.New("user not found: "+name))
 			return
 		}
 		if err != nil {
@@ -255,7 +256,7 @@ func (h *ownershipHandler) setCollaborators(w http.ResponseWriter, req *http.Req
 		err := h.db.DB.QueryRowContext(req.Context(),
 			`SELECT username FROM users WHERE id = ?`, id).Scan(&username)
 		if errors.Is(err, sql.ErrNoRows) {
-			http.Error(w, "user not found", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.ownership.user_not_found_400", nil))
 			return
 		}
 		if err != nil {
@@ -316,7 +317,7 @@ func (h *ownershipHandler) getOwnedServers(w http.ResponseWriter, req *http.Requ
 	}
 	u := auth.UserFromContext(req.Context())
 	if u == nil {
-		http.Error(w, "unauthenticated", http.StatusUnauthorized)
+		httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 		return
 	}
 
diff --git a/api/internal/handlers/registry_secret.go b/api/internal/handlers/registry_secret.go
index 8cb515667..25f7057a6 100644
--- a/api/internal/handlers/registry_secret.go
+++ b/api/internal/handlers/registry_secret.go
@@ -9,6 +9,7 @@ import (
 
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/registry"
 )
 
@@ -51,17 +52,17 @@ func (h registrySecretHandler) put(w http.ResponseWriter, req *http.Request) {
 		APIKey string `json:"apiKey"`
 	}
 	if err := json.NewDecoder(req.Body).Decode(&body); err != nil {
-		http.Error(w, "invalid json", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.common.invalid_json", nil))
 		return
 	}
 	if body.APIKey == "" {
-		http.Error(w, "apiKey is required", http.StatusUnprocessableEntity)
+		httperr.WriteMessage(w, req, messages.New("server.registry.api_key_required", nil))
 		return
 	}
 	data := map[string]string{"apiKey": body.APIKey}
 	if err := upsertLabelledSecret(req.Context(), h.k, h.ns, secretName, registry.RegistryKeySecretLabel, data); err != nil {
 		if errors.Is(err, errNotManagedSecret) {
-			http.Error(w, err.Error(), http.StatusConflict)
+			httperr.WriteCode(w, req, http.StatusConflict, err)
 			return
 		}
 		httperr.Write(w, req, err)
diff --git a/api/internal/handlers/resources.go b/api/internal/handlers/resources.go
index e307798e1..2e892ff5d 100644
--- a/api/internal/handlers/resources.go
+++ b/api/internal/handlers/resources.go
@@ -27,6 +27,7 @@ import (
 	"github.com/GameplanePanel/gameplane/api/internal/db"
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/scope"
 )
 
@@ -390,7 +391,7 @@ func deleteHandler(reg *kube.Registry, store *db.Store, gvr schema.GroupVersionR
 				// requests; direct handler fixtures may omit the caller.
 				if u := auth.UserFromContext(req.Context()); u != nil &&
 					!u.Can("*", true, scope.RequestedCluster(req), ns) && !isServerOwner(obj, u.ID) {
-					http.Error(w, "forbidden", http.StatusForbidden)
+					httperr.WriteMessage(w, req, messages.New("server.forbidden", nil))
 					return
 				}
 				options.Preconditions = objectDeletePreconditions(obj)
diff --git a/api/internal/handlers/roles.go b/api/internal/handlers/roles.go
index 6dbcc342c..40ce54fd7 100644
--- a/api/internal/handlers/roles.go
+++ b/api/internal/handlers/roles.go
@@ -12,6 +12,7 @@ import (
 	"github.com/GameplanePanel/gameplane/api/internal/auth"
 	"github.com/GameplanePanel/gameplane/api/internal/db"
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/rbac"
 	"github.com/GameplanePanel/gameplane/api/internal/scope"
 )
@@ -116,15 +117,15 @@ type roleCreateReq struct {
 func (h *roleHandler) create(w http.ResponseWriter, req *http.Request) {
 	var body roleCreateReq
 	if err := json.NewDecoder(req.Body).Decode(&body); err != nil {
-		http.Error(w, "bad request", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.bad_request", nil))
 		return
 	}
 	if !identifierRE.MatchString(body.Name) {
-		http.Error(w, "invalid role name", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.roles.invalid_role_name", nil))
 		return
 	}
 	if msg, ok := validatePermissions(body.Permissions); !ok {
-		http.Error(w, msg, http.StatusBadRequest)
+		httperr.WriteCode(w, req, http.StatusBadRequest, errors.New(msg))
 		return
 	}
 
@@ -139,7 +140,7 @@ func (h *roleHandler) create(w http.ResponseWriter, req *http.Request) {
 		`INSERT INTO roles(name, description, builtin) VALUES (?, ?, 0)`,
 		body.Name, body.Description); err != nil {
 		// A duplicate name is a client error, not a 500.
-		http.Error(w, "role already exists", http.StatusConflict)
+		httperr.WriteMessage(w, req, messages.New("server.roles.role_already_exists", nil))
 		return
 	}
 	if err := insertPermissions(req, tx, body.Name, body.Permissions); err != nil {
@@ -166,24 +167,24 @@ func (h *roleHandler) update(w http.ResponseWriter, req *http.Request) {
 		return
 	}
 	if !found {
-		http.Error(w, "role not found", http.StatusNotFound)
+		httperr.WriteMessage(w, req, messages.New("server.roles.role_not_found", nil))
 		return
 	}
 	// The admin role is the cluster's last-resort authority — its wildcard
 	// must stay intact, so it can't be edited. operator/viewer are editable.
 	if builtin && name == rbac.RoleAdmin {
-		http.Error(w, "the admin role cannot be edited", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.roles.admin_not_editable", nil))
 		return
 	}
 
 	var body roleUpdateReq
 	if err := json.NewDecoder(req.Body).Decode(&body); err != nil {
-		http.Error(w, "bad request", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.bad_request", nil))
 		return
 	}
 	if body.Permissions != nil {
 		if msg, ok := validatePermissions(*body.Permissions); !ok {
-			http.Error(w, msg, http.StatusBadRequest)
+			httperr.WriteCode(w, req, http.StatusBadRequest, errors.New(msg))
 			return
 		}
 		// Lock to serialize with writes so the last-user-manager check can't race.
@@ -198,7 +199,7 @@ func (h *roleHandler) update(w http.ResponseWriter, req *http.Request) {
 				return
 			}
 			if remoteBindings > 0 {
-				http.Error(w, "remove remote cluster-wide bindings before adding control-plane permissions", http.StatusBadRequest)
+				httperr.WriteMessage(w, req, messages.New("server.roles.remote_bindings_block_control_plane", nil))
 				return
 			}
 		}
@@ -206,7 +207,7 @@ func (h *roleHandler) update(w http.ResponseWriter, req *http.Request) {
 			httperr.Write(w, req, err)
 			return
 		} else if msg != "" {
-			http.Error(w, msg, http.StatusBadRequest)
+			httperr.WriteCode(w, req, http.StatusBadRequest, errors.New(msg))
 			return
 		}
 	}
@@ -258,7 +259,7 @@ func (h *roleHandler) update(w http.ResponseWriter, req *http.Request) {
 			return
 		}
 	}
-	http.Error(w, "role not found", http.StatusNotFound)
+	httperr.WriteMessage(w, req, messages.New("server.roles.role_not_found", nil))
 }
 
 func (h *roleHandler) del(w http.ResponseWriter, req *http.Request) {
@@ -273,11 +274,11 @@ func (h *roleHandler) del(w http.ResponseWriter, req *http.Request) {
 		return
 	}
 	if !found {
-		http.Error(w, "role not found", http.StatusNotFound)
+		httperr.WriteMessage(w, req, messages.New("server.roles.role_not_found", nil))
 		return
 	}
 	if builtin {
-		http.Error(w, "built-in roles cannot be deleted", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.roles.builtin_not_deletable", nil))
 		return
 	}
 	var inUse int
@@ -287,7 +288,7 @@ func (h *roleHandler) del(w http.ResponseWriter, req *http.Request) {
 		return
 	}
 	if inUse > 0 {
-		http.Error(w, "role is assigned to one or more users", http.StatusConflict)
+		httperr.WriteMessage(w, req, messages.New("server.roles.role_in_use", nil))
 		return
 	}
 
diff --git a/api/internal/handlers/shares.go b/api/internal/handlers/shares.go
index 2cb072eb2..e2289aabf 100644
--- a/api/internal/handlers/shares.go
+++ b/api/internal/handlers/shares.go
@@ -18,6 +18,7 @@ import (
 	"github.com/GameplanePanel/gameplane/api/internal/db"
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/scope"
 )
 
@@ -94,7 +95,7 @@ func createShareHandler(reg *kube.Registry, store *db.Store) http.HandlerFunc {
 	return func(w http.ResponseWriter, req *http.Request) {
 		u := auth.UserFromContext(req.Context())
 		if u == nil {
-			http.Error(w, "unauthenticated", http.StatusUnauthorized)
+			httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 			return
 		}
 		name := chi.URLParam(req, "name")
@@ -116,13 +117,13 @@ func createShareHandler(reg *kube.Registry, store *db.Store) http.HandlerFunc {
 			return
 		}
 		if !isServerOwner(obj, u.ID) {
-			http.Error(w, "forbidden", http.StatusForbidden)
+			httperr.WriteMessage(w, req, messages.New("server.forbidden", nil))
 			return
 		}
 
 		var body createShareReq
 		if err := json.NewDecoder(io.LimitReader(req.Body, 1<<16)).Decode(&body); err != nil {
-			http.Error(w, "bad request", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.bad_request", nil))
 			return
 		}
 
@@ -135,12 +136,12 @@ func createShareHandler(reg *kube.Registry, store *db.Store) http.HandlerFunc {
 		var expiresAt *time.Time
 		switch {
 		case hasExpiresAt && hasNeverExpires:
-			http.Error(w, "expiresAt and neverExpires are mutually exclusive", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.shares.expiry_mutually_exclusive", nil))
 			return
 		case hasExpiresAt:
 			parsed, err := time.Parse(time.RFC3339, *body.ExpiresAt)
 			if err != nil {
-				http.Error(w, "invalid expiresAt: must be RFC3339", http.StatusBadRequest)
+				httperr.WriteMessage(w, req, messages.New("server.shares.invalid_expires_at", nil))
 				return
 			}
 			parsed = parsed.UTC()
@@ -154,14 +155,14 @@ func createShareHandler(reg *kube.Registry, store *db.Store) http.HandlerFunc {
 			if *body.ExpiresIn != "" {
 				d, err := time.ParseDuration(*body.ExpiresIn)
 				if err != nil {
-					http.Error(w, "invalid expiresIn", http.StatusBadRequest)
+					httperr.WriteMessage(w, req, messages.New("server.shares.invalid_expires_in", nil))
 					return
 				}
 				at = time.Now().UTC().Add(d)
 			}
 			expiresAt = &at
 		default:
-			http.Error(w, "must specify exactly one of expiresAt or neverExpires (or the deprecated expiresIn)", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.shares.expiry_required", nil))
 			return
 		}
 
@@ -169,7 +170,7 @@ func createShareHandler(reg *kube.Registry, store *db.Store) http.HandlerFunc {
 		rawToken, link, err := store.CreateShareLinkForServer(req.Context(), cl, ns, name, string(obj.GetUID()), u.ID, body.CanStart, expiresAt)
 		if err != nil {
 			if errors.Is(err, db.ErrShareLinkExpiryInvalid) {
-				http.Error(w, "expiresAt must be in the future", http.StatusBadRequest)
+				httperr.WriteMessage(w, req, messages.New("server.shares.expires_at_in_past", nil))
 				return
 			}
 			httperr.Write(w, req, err)
@@ -194,7 +195,7 @@ func listSharesHandler(reg *kube.Registry, store *db.Store) http.HandlerFunc {
 	return func(w http.ResponseWriter, req *http.Request) {
 		u := auth.UserFromContext(req.Context())
 		if u == nil {
-			http.Error(w, "unauthenticated", http.StatusUnauthorized)
+			httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 			return
 		}
 		name := chi.URLParam(req, "name")
@@ -216,7 +217,7 @@ func listSharesHandler(reg *kube.Registry, store *db.Store) http.HandlerFunc {
 			return
 		}
 		if !isServerOwner(obj, u.ID) {
-			http.Error(w, "forbidden", http.StatusForbidden)
+			httperr.WriteMessage(w, req, messages.New("server.forbidden", nil))
 			return
 		}
 
@@ -248,7 +249,7 @@ func revokeShareHandler(reg *kube.Registry, store *db.Store) http.HandlerFunc {
 	return func(w http.ResponseWriter, req *http.Request) {
 		u := auth.UserFromContext(req.Context())
 		if u == nil {
-			http.Error(w, "unauthenticated", http.StatusUnauthorized)
+			httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 			return
 		}
 		name := chi.URLParam(req, "name")
@@ -271,14 +272,14 @@ func revokeShareHandler(reg *kube.Registry, store *db.Store) http.HandlerFunc {
 			return
 		}
 		if !isServerOwner(obj, u.ID) {
-			http.Error(w, "forbidden", http.StatusForbidden)
+			httperr.WriteMessage(w, req, messages.New("server.forbidden", nil))
 			return
 		}
 
 		cl, _ := scope.ResolveCluster(req, reg)
 		if err := store.RevokeShareLink(req.Context(), cl, ns, name, id); err != nil {
 			if errors.Is(err, db.ErrShareLinkNotFound) {
-				http.Error(w, "not found", http.StatusNotFound)
+				httperr.WriteMessage(w, req, messages.New("server.not_found", nil))
 				return
 			}
 			httperr.Write(w, req, err)
diff --git a/api/internal/handlers/telemetry.go b/api/internal/handlers/telemetry.go
index cda2728e2..9099d4b4f 100644
--- a/api/internal/handlers/telemetry.go
+++ b/api/internal/handlers/telemetry.go
@@ -14,6 +14,7 @@ import (
 	"github.com/GameplanePanel/gameplane/api/internal/auth"
 	"github.com/GameplanePanel/gameplane/api/internal/db"
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/telemetry"
 	"github.com/GameplanePanel/gameplane/telemetryschema"
 )
@@ -207,7 +208,7 @@ func (h *telemetryHandler) postInstallID(w http.ResponseWriter, req *http.Reques
 	})
 	switch {
 	case errors.Is(err, telemetry.ErrOperatorDisabled), errors.Is(err, errExtendedOff):
-		http.Error(w, err.Error(), http.StatusConflict)
+		httperr.WriteCode(w, req, http.StatusConflict, err)
 	case err != nil:
 		httperr.Write(w, req, err)
 	default:
@@ -273,20 +274,20 @@ func (h *telemetryHandler) postNotice(w http.ResponseWriter, req *http.Request)
 	ctx := req.Context()
 	u := auth.UserFromContext(ctx)
 	if u == nil {
-		http.Error(w, "unauthorized", http.StatusUnauthorized)
+		httperr.WriteMessage(w, req, messages.New("server.unauthorized", nil))
 		return
 	}
 	var body struct {
 		Action string `json:"action"`
 	}
 	if err := json.NewDecoder(http.MaxBytesReader(w, req.Body, 1<<10)).Decode(&body); err != nil {
-		http.Error(w, "invalid json", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.common.invalid_json", nil))
 		return
 	}
 	switch body.Action {
 	case noticeSeen, noticeKeep, noticeExtendedOff, noticeAllOff:
 	default:
-		http.Error(w, "action must be one of seen|keep|extended-off|all-off", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.telemetry.invalid_notice_action", nil))
 		return
 	}
 	pending, err := h.pending(ctx, u)
@@ -299,7 +300,7 @@ func (h *telemetryHandler) postNotice(w http.ResponseWriter, req *http.Request)
 			w.WriteHeader(http.StatusNoContent) // a no-op, not an error
 			return
 		}
-		http.Error(w, "telemetry notice is not pending", http.StatusConflict)
+		httperr.WriteMessage(w, req, messages.New("server.telemetry.notice_not_pending", nil))
 		return
 	}
 	err = inTx(ctx, h.db, func(tx *sql.Tx) error {
@@ -307,7 +308,7 @@ func (h *telemetryHandler) postNotice(w http.ResponseWriter, req *http.Request)
 	})
 	switch {
 	case errors.Is(err, telemetry.ErrOperatorDisabled):
-		http.Error(w, err.Error(), http.StatusConflict)
+		httperr.WriteCode(w, req, http.StatusConflict, err)
 	case err != nil:
 		httperr.Write(w, req, err)
 	default:
diff --git a/api/internal/handlers/tunnelcreds.go b/api/internal/handlers/tunnelcreds.go
index 764531087..460ac0ed1 100644
--- a/api/internal/handlers/tunnelcreds.go
+++ b/api/internal/handlers/tunnelcreds.go
@@ -16,6 +16,7 @@ import (
 
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 )
 
 // Provider key names as documented in docs/tunnels.md.
@@ -73,20 +74,20 @@ func (h *tunnelCredsHandler) put(w http.ResponseWriter, req *http.Request) {
 
 	var body putReq
 	if err := json.NewDecoder(io.LimitReader(req.Body, 1<<16)).Decode(&body); err != nil {
-		http.Error(w, "invalid request body", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.tunnel.invalid_request_body", nil))
 		return
 	}
 
 	// Validate provider is known.
 	expectedKeys, ok := tunnelProviderKeys[body.Provider]
 	if !ok {
-		http.Error(w, fmt.Sprintf("unknown provider: %s", body.Provider), http.StatusBadRequest)
+		httperr.WriteCode(w, req, http.StatusBadRequest, fmt.Errorf("unknown provider: %s", body.Provider))
 		return
 	}
 
 	// Validate values match provider's expected keys.
 	if err := validateTunnelValues(body.Values, expectedKeys); err != nil {
-		http.Error(w, err.Error(), http.StatusBadRequest)
+		httperr.WriteCode(w, req, http.StatusBadRequest, err)
 		return
 	}
 
@@ -131,7 +132,7 @@ func (h *tunnelCredsHandler) put(w http.ResponseWriter, req *http.Request) {
 			return
 		}
 		if !isServerOwnedSecretObject(existing, name, gs.GetUID()) {
-			http.Error(w, "conflict: existing secret is not owned by this server", http.StatusConflict)
+			httperr.WriteMessage(w, req, messages.New("server.tunnel.secret_not_owned_conflict", nil))
 			return
 		}
 
@@ -274,7 +275,7 @@ func (h *tunnelCredsHandler) delete(w http.ResponseWriter, req *http.Request) {
 		return
 	}
 	if ok && tunnelEnabled {
-		http.Error(w, "cannot delete tunnel credentials while tunnel is enabled; disable the tunnel first or use PUT to rotate credentials", http.StatusConflict)
+		httperr.WriteMessage(w, req, messages.New("server.tunnel.credentials_in_use", nil))
 		return
 	}
 
@@ -292,7 +293,7 @@ func (h *tunnelCredsHandler) delete(w http.ResponseWriter, req *http.Request) {
 		existing, err := k.Typed.CoreV1().Secrets(ns).Get(req.Context(), secretRef, metav1.GetOptions{})
 		if err == nil {
 			if !isServerOwnedSecretObject(existing, name, gs.GetUID()) {
-				http.Error(w, "forbidden: cannot delete secret not owned by this server", http.StatusForbidden)
+				httperr.WriteMessage(w, req, messages.New("server.tunnel.secret_not_owned_forbidden", nil))
 				return
 			}
 			checkedSecret = existing
diff --git a/api/internal/handlers/users.go b/api/internal/handlers/users.go
index 65231cb1f..ea5608335 100644
--- a/api/internal/handlers/users.go
+++ b/api/internal/handlers/users.go
@@ -19,9 +19,15 @@ import (
 	"github.com/GameplanePanel/gameplane/api/internal/auth"
 	"github.com/GameplanePanel/gameplane/api/internal/db"
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/scope"
+	"github.com/GameplanePanel/gameplane/i18n/catalog"
 )
 
+// languageListed reports whether a language tag is offered by this release.
+// It is a variable so tests can point it at a tag the shipped catalog lists.
+var languageListed = catalog.IsListed
+
 // MountUsers registers the user management API handlers.
 func MountUsers(r chi.Router, store *db.Store, sessions *auth.SessionStore, clusters scope.ClusterLister) {
 	h := &userHandler{db: store, sessions: sessions, clusters: clusters}
@@ -32,6 +38,7 @@ func MountUsers(r chi.Router, store *db.Store, sessions *auth.SessionStore, clus
 		r.Get("/me/preferences", h.getPreferences)
 		r.Put("/me/preferences", h.putPreferences)
 		r.Post("/me/preferences/reset", h.resetPreferences)
+		r.Put("/me/language", h.putLanguage)
 		r.Delete("/{id}", h.del)
 		r.Patch("/{id}", h.update)
 		r.Post("/{id}/reset-password", h.resetPassword)
@@ -113,16 +120,16 @@ type createUserReq struct {
 func (h *userHandler) create(w http.ResponseWriter, req *http.Request) {
 	var body createUserReq
 	if err := json.NewDecoder(req.Body).Decode(&body); err != nil {
-		http.Error(w, "bad request", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.bad_request", nil))
 		return
 	}
 	if !identifierRE.MatchString(body.Username) {
-		http.Error(w, "invalid username", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.invalid_username", nil))
 		return
 	}
 	if body.Email != "" {
 		if _, err := mail.ParseAddress(body.Email); err != nil {
-			http.Error(w, "invalid email", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.users.invalid_email", nil))
 			return
 		}
 	}
@@ -133,13 +140,13 @@ func (h *userHandler) create(w http.ResponseWriter, req *http.Request) {
 		httperr.Write(w, req, err)
 		return
 	} else if !ok {
-		http.Error(w, "invalid role", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.invalid_role", nil))
 		return
 	}
 	var hash string
 	if body.Password != "" {
 		if len(body.Password) < auth.MinPasswordLen {
-			http.Error(w, "password too short", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.users.password_too_short", nil))
 			return
 		}
 		h2, err := auth.HashPassword(req.Context(), body.Password)
@@ -181,7 +188,7 @@ func (h *userHandler) create(w http.ResponseWriter, req *http.Request) {
 func (h *userHandler) me(w http.ResponseWriter, req *http.Request) {
 	u := auth.UserFromContext(req.Context())
 	if u == nil {
-		http.Error(w, "unauthenticated", http.StatusUnauthorized)
+		httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 		return
 	}
 	prefs, err := h.db.GetPreferences(req.Context(), u.ID)
@@ -213,7 +220,10 @@ type userPreferencesDTO struct {
 	CustomColors     *customColorsDTO `json:"customColors"`
 	CustomCSSEnabled bool             `json:"customCssEnabled"`
 	CustomCSS        *string          `json:"customCss"`
-	UpdatedAt        string           `json:"updatedAt"`
+	// Language is the user's saved language tag, null when the user follows
+	// the instance default. It is set through PUT /users/me/language.
+	Language  *string `json:"language"`
+	UpdatedAt string  `json:"updatedAt"`
 }
 
 func preferencesDTO(p db.UserPreferences) *userPreferencesDTO {
@@ -223,6 +233,7 @@ func preferencesDTO(p db.UserPreferences) *userPreferencesDTO {
 		AppearanceMode:   p.AppearanceMode,
 		CustomCSSEnabled: p.CustomCSSEnabled,
 		CustomCSS:        p.CustomCSS,
+		Language:         p.Language,
 		UpdatedAt:        p.UpdatedAt,
 	}
 	if p.CustomAccent != nil || p.CustomSurface != nil {
@@ -284,7 +295,7 @@ func sanitizeCustomCSS(css string) string {
 func (h *userHandler) getPreferences(w http.ResponseWriter, req *http.Request) {
 	u := auth.UserFromContext(req.Context())
 	if u == nil {
-		http.Error(w, "unauthenticated", http.StatusUnauthorized)
+		httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 		return
 	}
 	prefs, err := h.db.GetPreferences(req.Context(), u.ID)
@@ -316,55 +327,55 @@ type customColorsReq struct {
 func (h *userHandler) putPreferences(w http.ResponseWriter, req *http.Request) {
 	u := auth.UserFromContext(req.Context())
 	if u == nil {
-		http.Error(w, "unauthenticated", http.StatusUnauthorized)
+		httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 		return
 	}
 	var body updatePreferencesReq
 	if err := json.NewDecoder(req.Body).Decode(&body); err != nil {
-		http.Error(w, "bad request", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.bad_request", nil))
 		return
 	}
 	if body.ThemeType == nil {
-		http.Error(w, "themeType is required", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.theme_type_required", nil))
 		return
 	}
 	if *body.ThemeType != "preset" && *body.ThemeType != "custom_colors" {
-		http.Error(w, `themeType must be "preset" or "custom_colors"`, http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.theme_type_invalid", nil))
 		return
 	}
 	if body.PresetID == nil {
-		http.Error(w, "presetId is required", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.preset_id_required", nil))
 		return
 	}
 	if *body.PresetID != "pink" && *body.PresetID != "legacy" {
-		http.Error(w, `presetId must be "pink" or "legacy"`, http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.preset_id_invalid", nil))
 		return
 	}
 	if body.AppearanceMode == nil {
-		http.Error(w, "appearanceMode is required", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.appearance_mode_required", nil))
 		return
 	}
 	if *body.AppearanceMode != "light" && *body.AppearanceMode != "dark" && *body.AppearanceMode != "system" {
-		http.Error(w, `appearanceMode must be "light", "dark" or "system"`, http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.appearance_mode_invalid", nil))
 		return
 	}
 	if body.CustomCSSEnabled == nil {
-		http.Error(w, "customCssEnabled is required", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.custom_css_enabled_required", nil))
 		return
 	}
 	if body.CustomColors != nil {
 		if body.CustomColors.Accent != nil && !hexColorRE.MatchString(*body.CustomColors.Accent) {
-			http.Error(w, "customColors.accent must be a #RRGGBB hex color", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.users.custom_accent_invalid", nil))
 			return
 		}
 		if body.CustomColors.Surface != nil && !hexColorRE.MatchString(*body.CustomColors.Surface) {
-			http.Error(w, "customColors.surface must be a #RRGGBB hex color", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.users.custom_surface_invalid", nil))
 			return
 		}
 	}
 	if body.CustomCSS != nil {
 		if msg := sanitizeCustomCSS(*body.CustomCSS); msg != "" {
-			http.Error(w, msg, http.StatusBadRequest)
+			httperr.WriteCode(w, req, http.StatusBadRequest, errors.New(msg))
 			return
 		}
 	}
@@ -410,12 +421,12 @@ type resetPreferencesReq struct {
 func (h *userHandler) resetPreferences(w http.ResponseWriter, req *http.Request) {
 	u := auth.UserFromContext(req.Context())
 	if u == nil {
-		http.Error(w, "unauthenticated", http.StatusUnauthorized)
+		httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 		return
 	}
 	var body resetPreferencesReq
 	if err := json.NewDecoder(req.Body).Decode(&body); err != nil && !errors.Is(err, io.EOF) {
-		http.Error(w, "bad request", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.bad_request", nil))
 		return
 	}
 	// Resolve the target preset/appearance from the body, defaulting to the
@@ -427,14 +438,14 @@ func (h *userHandler) resetPreferences(w http.ResponseWriter, req *http.Request)
 	}
 	if body.PresetID != nil {
 		if *body.PresetID != "pink" && *body.PresetID != "legacy" {
-			http.Error(w, `presetId must be "pink" or "legacy"`, http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.users.preset_id_invalid", nil))
 			return
 		}
 		prefs.PresetID = *body.PresetID
 	}
 	if body.AppearanceMode != nil {
 		if *body.AppearanceMode != "light" && *body.AppearanceMode != "dark" && *body.AppearanceMode != "system" {
-			http.Error(w, `appearanceMode must be "light", "dark" or "system"`, http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.users.appearance_mode_invalid", nil))
 			return
 		}
 		prefs.AppearanceMode = *body.AppearanceMode
@@ -444,18 +455,65 @@ func (h *userHandler) resetPreferences(w http.ResponseWriter, req *http.Request)
 		httperr.Write(w, req, err)
 		return
 	}
+	// Reset clears styling only; the saved language is kept.
+	saved.Language = prefs.Language
 	writeJSON(w, preferencesDTO(saved))
 }
 
+// languageReq is the PUT /users/me/language body. Language is kept raw so a
+// missing key (an error) can be told apart from an explicit null (clear).
+type languageReq struct {
+	Language json.RawMessage `json:"language"`
+}
+
+// putLanguage stores the user's language choice. A null clears it back to
+// the instance default. A non-null tag must be one this release offers.
+func (h *userHandler) putLanguage(w http.ResponseWriter, req *http.Request) {
+	u := auth.UserFromContext(req.Context())
+	if u == nil {
+		httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
+		return
+	}
+	var body languageReq
+	dec := json.NewDecoder(req.Body)
+	dec.DisallowUnknownFields()
+	if err := dec.Decode(&body); err != nil {
+		httperr.WriteCode(w, req, http.StatusBadRequest, errors.New("bad request"))
+		return
+	}
+	if len(body.Language) == 0 {
+		httperr.WriteCode(w, req, http.StatusBadRequest, errors.New("language is required"))
+		return
+	}
+	var language *string
+	if string(body.Language) != "null" {
+		var tag string
+		if err := json.Unmarshal(body.Language, &tag); err != nil {
+			httperr.WriteCode(w, req, http.StatusBadRequest, errors.New("language must be a string or null"))
+			return
+		}
+		if !languageListed(tag) {
+			httperr.WriteMessage(w, req, messages.New("server.i18n.unknown_language", map[string]any{"language": tag}))
+			return
+		}
+		language = &tag
+	}
+	if err := h.db.SetLanguage(req.Context(), u.ID, language); err != nil {
+		httperr.Write(w, req, err)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
+
 func (h *userHandler) del(w http.ResponseWriter, req *http.Request) {
 	id, err := strconv.ParseInt(chi.URLParam(req, "id"), 10, 64)
 	if err != nil {
-		http.Error(w, "bad id", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.bad_id", nil))
 		return
 	}
 	u := auth.UserFromContext(req.Context())
 	if u != nil && u.ID == id {
-		http.Error(w, "cannot delete self", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.cannot_delete_self", nil))
 		return
 	}
 	// Lock to serialize with writes so the last-user-manager check can't race.
@@ -472,7 +530,7 @@ func (h *userHandler) del(w http.ResponseWriter, req *http.Request) {
 			return
 		}
 		if count <= 1 {
-			http.Error(w, "cannot delete the last user who can manage users", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.users.cannot_delete_last_manager", nil))
 			return
 		}
 	}
@@ -498,17 +556,17 @@ type updateUserReq struct {
 func (h *userHandler) update(w http.ResponseWriter, req *http.Request) {
 	id, err := strconv.ParseInt(chi.URLParam(req, "id"), 10, 64)
 	if err != nil {
-		http.Error(w, "bad id", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.bad_id", nil))
 		return
 	}
 	var body updateUserReq
 	if err := json.NewDecoder(req.Body).Decode(&body); err != nil {
-		http.Error(w, "bad request", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.bad_request", nil))
 		return
 	}
 	if body.Email != nil && *body.Email != "" {
 		if _, err := mail.ParseAddress(*body.Email); err != nil {
-			http.Error(w, "invalid email", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.users.invalid_email", nil))
 			return
 		}
 	}
@@ -517,7 +575,7 @@ func (h *userHandler) update(w http.ResponseWriter, req *http.Request) {
 			httperr.Write(w, req, err)
 			return
 		} else if !ok {
-			http.Error(w, "invalid role", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.users.invalid_role", nil))
 			return
 		}
 	}
@@ -536,7 +594,7 @@ func (h *userHandler) update(w http.ResponseWriter, req *http.Request) {
 		// users (the generalization of the old "don't demote yourself out
 		// of admin" guard) — someone else must do it.
 		if selfChanging && !newGrantsManage {
-			http.Error(w, "cannot remove your own user-management access", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.users.cannot_remove_own_management", nil))
 			return
 		}
 		// System-wide safety net: never demote the last user who can manage
@@ -552,7 +610,7 @@ func (h *userHandler) update(w http.ResponseWriter, req *http.Request) {
 					return
 				}
 				if count <= 1 {
-					http.Error(w, "cannot demote the last user who can manage users", http.StatusBadRequest)
+					httperr.WriteMessage(w, req, messages.New("server.users.cannot_demote_last_manager", nil))
 					return
 				}
 			}
@@ -620,7 +678,7 @@ func (h *userHandler) update(w http.ResponseWriter, req *http.Request) {
 	out, err := h.fetchByID(req.Context(), id)
 	if err != nil {
 		if errors.Is(err, sql.ErrNoRows) {
-			http.Error(w, "user not found", http.StatusNotFound)
+			httperr.WriteMessage(w, req, messages.New("server.common.user_not_found", nil))
 			return
 		}
 		httperr.Write(w, req, err)
@@ -636,16 +694,16 @@ type resetPasswordReq struct {
 func (h *userHandler) resetPassword(w http.ResponseWriter, req *http.Request) {
 	id, err := strconv.ParseInt(chi.URLParam(req, "id"), 10, 64)
 	if err != nil {
-		http.Error(w, "bad id", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.bad_id", nil))
 		return
 	}
 	var body resetPasswordReq
 	if err := json.NewDecoder(req.Body).Decode(&body); err != nil {
-		http.Error(w, "bad request", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.bad_request", nil))
 		return
 	}
 	if len(body.Password) < auth.MinPasswordLen {
-		http.Error(w, "password too short", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.password_too_short", nil))
 		return
 	}
 	hash, err := auth.HashPassword(req.Context(), body.Password)
@@ -662,7 +720,7 @@ func (h *userHandler) resetPassword(w http.ResponseWriter, req *http.Request) {
 	}
 	n, _ := res.RowsAffected()
 	if n == 0 {
-		http.Error(w, "user not found", http.StatusNotFound)
+		httperr.WriteMessage(w, req, messages.New("server.common.user_not_found", nil))
 		return
 	}
 	// Force the target user to re-authenticate under the new credential.
@@ -685,7 +743,7 @@ type bindingDTO struct {
 func (h *userHandler) listBindings(w http.ResponseWriter, req *http.Request) {
 	id, err := strconv.ParseInt(chi.URLParam(req, "id"), 10, 64)
 	if err != nil {
-		http.Error(w, "bad id", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.bad_id", nil))
 		return
 	}
 	rows, err := h.db.DB.QueryContext(req.Context(),
@@ -720,12 +778,12 @@ type addBindingReq struct {
 func (h *userHandler) addBinding(w http.ResponseWriter, req *http.Request) {
 	id, err := strconv.ParseInt(chi.URLParam(req, "id"), 10, 64)
 	if err != nil {
-		http.Error(w, "bad id", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.bad_id", nil))
 		return
 	}
 	var body addBindingReq
 	if err := json.NewDecoder(req.Body).Decode(&body); err != nil {
-		http.Error(w, "bad request", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.bad_request", nil))
 		return
 	}
 	// Default the cluster to the default cluster.
@@ -736,12 +794,12 @@ func (h *userHandler) addBinding(w http.ResponseWriter, req *http.Request) {
 	// An explicit remote-wide grant may carry only inventory/namespaced access.
 	remoteWide := body.Namespace == "*" && body.Cluster != scope.DefaultCluster
 	if !remoteWide && (body.Namespace == "*" || !scope.Allowed(body.Namespace)) {
-		http.Error(w, "namespace not permitted", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.common.namespace_not_permitted", nil))
 		return
 	}
 	// Validate the cluster.
 	if body.Cluster == "*" {
-		http.Error(w, "cluster not permitted", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.cluster_forbidden", nil))
 		return
 	}
 	known := false
@@ -752,7 +810,7 @@ func (h *userHandler) addBinding(w http.ResponseWriter, req *http.Request) {
 		}
 	}
 	if !known {
-		http.Error(w, "cluster not permitted", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.cluster_forbidden", nil))
 		return
 	}
 	if remoteWide {
@@ -765,7 +823,7 @@ func (h *userHandler) addBinding(w http.ResponseWriter, req *http.Request) {
 		httperr.Write(w, req, err)
 		return
 	} else if !ok {
-		http.Error(w, "invalid role", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.invalid_role", nil))
 		return
 	}
 	if remoteWide {
@@ -773,7 +831,7 @@ func (h *userHandler) addBinding(w http.ResponseWriter, req *http.Request) {
 			httperr.Write(w, req, err)
 			return
 		} else if !allowed {
-			http.Error(w, "remote cluster-wide roles may grant only cluster:read and namespaced permissions", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.users.remote_role_scope_limited", nil))
 			return
 		}
 	}
@@ -781,7 +839,7 @@ func (h *userHandler) addBinding(w http.ResponseWriter, req *http.Request) {
 		httperr.Write(w, req, err)
 		return
 	} else if !ok {
-		http.Error(w, "user not found", http.StatusNotFound)
+		httperr.WriteMessage(w, req, messages.New("server.common.user_not_found", nil))
 		return
 	}
 	var dup int
@@ -792,7 +850,7 @@ func (h *userHandler) addBinding(w http.ResponseWriter, req *http.Request) {
 		return
 	}
 	if dup > 0 {
-		http.Error(w, "binding already exists", http.StatusConflict)
+		httperr.WriteMessage(w, req, messages.New("server.users.binding_already_exists", nil))
 		return
 	}
 	if _, err := h.db.DB.ExecContext(req.Context(),
@@ -808,7 +866,7 @@ func (h *userHandler) addBinding(w http.ResponseWriter, req *http.Request) {
 func (h *userHandler) deleteBinding(w http.ResponseWriter, req *http.Request) {
 	id, err := strconv.ParseInt(chi.URLParam(req, "id"), 10, 64)
 	if err != nil {
-		http.Error(w, "bad id", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.bad_id", nil))
 		return
 	}
 	role := chi.URLParam(req, "role")
@@ -818,11 +876,11 @@ func (h *userHandler) deleteBinding(w http.ResponseWriter, req *http.Request) {
 		cluster = scope.DefaultCluster
 	}
 	if namespace == "*" && cluster == scope.DefaultCluster {
-		http.Error(w, "the cluster-wide role is managed via the primary role", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.users.cluster_role_is_primary", nil))
 		return
 	}
 	if cluster == "*" {
-		http.Error(w, "cluster not permitted", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.cluster_forbidden", nil))
 		return
 	}
 	if namespace == "*" {
@@ -834,7 +892,7 @@ func (h *userHandler) deleteBinding(w http.ResponseWriter, req *http.Request) {
 			httperr.Write(w, req, err)
 			return
 		} else if !allowed {
-			http.Error(w, "remote control-plane bindings cannot be removed through supplemental grants", http.StatusBadRequest)
+			httperr.WriteMessage(w, req, messages.New("server.users.remote_binding_not_removable", nil))
 			return
 		}
 	}
@@ -846,7 +904,7 @@ func (h *userHandler) deleteBinding(w http.ResponseWriter, req *http.Request) {
 		return
 	}
 	if n, _ := res.RowsAffected(); n == 0 {
-		http.Error(w, "binding not found", http.StatusNotFound)
+		httperr.WriteMessage(w, req, messages.New("server.users.binding_not_found", nil))
 		return
 	}
 	h.invalidateSessions(req, id, "role binding removed")
diff --git a/api/internal/handlers/users_language_test.go b/api/internal/handlers/users_language_test.go
new file mode 100644
index 000000000..4edec15e1
--- /dev/null
+++ b/api/internal/handlers/users_language_test.go
@@ -0,0 +1,199 @@
+package handlers
+
+import (
+	"bytes"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+// doLanguageReq sends a request as userID, optionally with an Accept header,
+// and returns the status, content type and body.
+func doLanguageReq(t *testing.T, srv *httptest.Server, userID int64, method, path, accept, rawBody string) (int, string, []byte) {
+	t.Helper()
+	var buf io.Reader
+	if rawBody != "" {
+		buf = bytes.NewReader([]byte(rawBody))
+	}
+	req, err := http.NewRequestWithContext(t.Context(), method, srv.URL+path, buf)
+	if err != nil {
+		t.Fatalf("new request: %v", err)
+	}
+	if rawBody != "" {
+		req.Header.Set("Content-Type", "application/json")
+	}
+	if userID != 0 {
+		req.Header.Set("X-Test-User-ID", strconv.FormatInt(userID, 10))
+	}
+	if accept != "" {
+		req.Header.Set("Accept", accept)
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatalf("do: %v", err)
+	}
+	defer resp.Body.Close()
+	out, _ := io.ReadAll(resp.Body)
+	return resp.StatusCode, resp.Header.Get("Content-Type"), out
+}
+
+// storedLanguage reads the language back through GET /users/me/preferences.
+func storedLanguage(t *testing.T, srv *httptest.Server, userID int64) *string {
+	t.Helper()
+	status, _, body := doLanguageReq(t, srv, userID, http.MethodGet, "/users/me/preferences", "", "")
+	if status != http.StatusOK {
+		t.Fatalf("get preferences: status %d body=%s", status, body)
+	}
+	return decodePrefs(t, body).Language
+}
+
+func TestPutLanguage_AcceptedThenReadBack(t *testing.T) {
+	store := newTestStore(t)
+	srv := newPreferencesServer(t, store)
+	userID := seedUser(t, store, "lang-putter", "viewer", "")
+
+	status, _, body := doLanguageReq(t, srv, userID, http.MethodPut, "/users/me/language", "", `{"language":"en"}`)
+	if status != http.StatusNoContent {
+		t.Fatalf("PUT en: status %d body=%s", status, body)
+	}
+	if got := storedLanguage(t, srv, userID); got == nil || *got != "en" {
+		t.Fatalf("stored language = %v, want en", got)
+	}
+}
+
+func TestPutLanguage_NullClears(t *testing.T) {
+	store := newTestStore(t)
+	srv := newPreferencesServer(t, store)
+	userID := seedUser(t, store, "lang-clearer", "viewer", "")
+
+	if status, _, body := doLanguageReq(t, srv, userID, http.MethodPut, "/users/me/language", "", `{"language":"en"}`); status != http.StatusNoContent {
+		t.Fatalf("seed en: status %d body=%s", status, body)
+	}
+	status, _, body := doLanguageReq(t, srv, userID, http.MethodPut, "/users/me/language", "", `{"language":null}`)
+	if status != http.StatusNoContent {
+		t.Fatalf("PUT null: status %d body=%s", status, body)
+	}
+	if got := storedLanguage(t, srv, userID); got != nil {
+		t.Fatalf("stored language = %q after null, want nil", *got)
+	}
+}
+
+func TestPutLanguage_UnknownTagPlainText(t *testing.T) {
+	store := newTestStore(t)
+	srv := newPreferencesServer(t, store)
+	userID := seedUser(t, store, "lang-plain", "viewer", "")
+
+	status, ctype, body := doLanguageReq(t, srv, userID, http.MethodPut, "/users/me/language", "", `{"language":"xx"}`)
+	if status != http.StatusBadRequest {
+		t.Fatalf("PUT xx: status %d, want 400 body=%s", status, body)
+	}
+	if strings.Contains(ctype, "problem+json") {
+		t.Fatalf("plain caller got content type %q", ctype)
+	}
+	if string(body) != "unknown language: xx\n" {
+		t.Fatalf("plain body = %q, want %q", body, "unknown language: xx\n")
+	}
+}
+
+func TestPutLanguage_UnknownTagProblemDocument(t *testing.T) {
+	store := newTestStore(t)
+	srv := newPreferencesServer(t, store)
+	userID := seedUser(t, store, "lang-problem", "viewer", "")
+
+	status, ctype, body := doLanguageReq(t, srv, userID, http.MethodPut, "/users/me/language", "application/problem+json", `{"language":"xx"}`)
+	if status != http.StatusBadRequest {
+		t.Fatalf("PUT xx problem: status %d, want 400 body=%s", status, body)
+	}
+	if !strings.Contains(ctype, "problem+json") {
+		t.Fatalf("content type = %q, want problem+json", ctype)
+	}
+	var doc struct {
+		MessageID string         `json:"messageId"`
+		Args      map[string]any `json:"args"`
+	}
+	if err := json.Unmarshal(body, &doc); err != nil {
+		t.Fatalf("decode problem: %v; body=%s", err, body)
+	}
+	if doc.MessageID != "server.i18n.unknown_language" {
+		t.Fatalf("messageId = %q, want server.i18n.unknown_language", doc.MessageID)
+	}
+	if doc.Args["language"] != "xx" {
+		t.Fatalf("args.language = %v, want xx", doc.Args["language"])
+	}
+}
+
+// A tag the shipped catalog does not list is rejected even when it looks valid.
+// languageListed is overridden for "fr" only, and restored afterwards.
+func TestPutLanguage_ShippedButUnlistedRejected(t *testing.T) {
+	prev := languageListed
+	languageListed = func(tag string) bool {
+		if tag == "fr" {
+			return false
+		}
+		return prev(tag)
+	}
+	t.Cleanup(func() { languageListed = prev })
+
+	store := newTestStore(t)
+	srv := newPreferencesServer(t, store)
+	userID := seedUser(t, store, "lang-unlisted", "viewer", "")
+
+	status, _, body := doLanguageReq(t, srv, userID, http.MethodPut, "/users/me/language", "", `{"language":"fr"}`)
+	if status != http.StatusBadRequest {
+		t.Fatalf("PUT fr: status %d, want 400 body=%s", status, body)
+	}
+	if string(body) != "unknown language: fr\n" {
+		t.Fatalf("body = %q", body)
+	}
+	if got := storedLanguage(t, srv, userID); got != nil {
+		t.Fatalf("stored language = %q after rejected PUT, want nil", *got)
+	}
+}
+
+func TestPutLanguage_MissingKeyRejected(t *testing.T) {
+	store := newTestStore(t)
+	srv := newPreferencesServer(t, store)
+	userID := seedUser(t, store, "lang-missing", "viewer", "")
+
+	status, _, body := doLanguageReq(t, srv, userID, http.MethodPut, "/users/me/language", "", `{}`)
+	if status != http.StatusBadRequest {
+		t.Fatalf("PUT {}: status %d, want 400 body=%s", status, body)
+	}
+	if string(body) != "language is required\n" {
+		t.Fatalf("body = %q", body)
+	}
+}
+
+func TestPutLanguage_UnauthenticatedRejected(t *testing.T) {
+	store := newTestStore(t)
+	srv := newPreferencesServer(t, store)
+
+	status, _, _ := doLanguageReq(t, srv, 0, http.MethodPut, "/users/me/language", "", `{"language":"en"}`)
+	if status != http.StatusUnauthorized {
+		t.Fatalf("unauthenticated PUT: status %d, want 401", status)
+	}
+}
+
+// PUT /users/me/preferences must accept a body that carries a language key
+// without changing the saved language.
+func TestPutPreferences_IgnoresLanguageKey(t *testing.T) {
+	store := newTestStore(t)
+	srv := newPreferencesServer(t, store)
+	userID := seedUser(t, store, "lang-prefs-ignore", "viewer", "")
+
+	if status, _, body := doLanguageReq(t, srv, userID, http.MethodPut, "/users/me/language", "", `{"language":"en"}`); status != http.StatusNoContent {
+		t.Fatalf("seed en: status %d body=%s", status, body)
+	}
+	status, _, body := doLanguageReq(t, srv, userID, http.MethodPut, "/users/me/preferences",
+		"", `{"themeType":"preset","presetId":"pink","appearanceMode":"dark","customCssEnabled":false,"language":"xx"}`)
+	if status != http.StatusOK {
+		t.Fatalf("PUT preferences with language key: status %d body=%s", status, body)
+	}
+	if got := storedLanguage(t, srv, userID); got == nil || *got != "en" {
+		t.Fatalf("stored language = %v, want en unchanged", got)
+	}
+}
diff --git a/api/internal/httperr/httperr.go b/api/internal/httperr/httperr.go
index 7668ec652..106f6db28 100644
--- a/api/internal/httperr/httperr.go
+++ b/api/internal/httperr/httperr.go
@@ -4,13 +4,23 @@
 // The default path previously echoed err.Error() directly, which leaked
 // K8s API paths, database column names, FS paths, and other detail to
 // unauthenticated or minimally-authed callers.
+//
+// Every response is available in two shapes. The default is the plain-text
+// body http.Error has always written. A caller whose Accept header asks for
+// application/problem+json (RFC 9457) instead receives a problem document
+// that also carries a stable messageId and the message arguments, so the
+// dashboard can localize the text. The plain-text body is unchanged.
 package httperr
 
 import (
+	"encoding/json"
 	"errors"
+	"fmt"
 	"io"
 	"log/slog"
 	"net/http"
+	"strconv"
+	"strings"
 
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 
@@ -23,6 +33,142 @@ import (
 // no cross-cluster agent yet to serve such a request on the remote cluster.
 const RemoteClusterNotImplemented = "not implemented: no cross-cluster agent yet; this route only serves the home cluster"
 
+// problemJSON is the media type of an RFC 9457 problem document.
+const problemJSON = "application/problem+json"
+
+// Message is a localizable error: a registry id, its arguments, the HTTP
+// status and the English text (the plain-text body, unchanged).
+type Message struct {
+	ID      string
+	Args    map[string]any
+	Status  int
+	English string
+}
+
+// Error implements error with the English text.
+func (m *Message) Error() string { return m.English }
+
+// Message ids httperr itself emits (registered in api/internal/messages).
+const (
+	IDNamespaceForbidden          = "server.namespace_forbidden"            // "namespace not permitted"
+	IDClusterForbidden            = "server.cluster_forbidden"              // "cluster not permitted"
+	IDNotFound                    = "server.not_found"                      // "not found"
+	IDAlreadyExists               = "server.already_exists"                 // "already exists"
+	IDConflictRetry               = "server.conflict_retry"                 // "conflict, retry"
+	IDForbidden                   = "server.forbidden"                      // "forbidden"
+	IDUnauthorized                = "server.unauthorized"                   // "unauthorized"
+	IDInvalid                     = "server.invalid"                        // "{detail}" — apierrors Invalid message (or "invalid")
+	IDBadRequest                  = "server.bad_request"                    // "bad request"
+	IDEmptyBody                   = "server.empty_body"                     // "empty body"
+	IDInternal                    = "server.internal"                       // "internal error"
+	IDRemoteClusterNotImplemented = "server.remote_cluster_not_implemented" // RemoteClusterNotImplemented
+)
+
+// GenericID is the id of the generic sentence registered for an HTTP
+// status, shown before the detail text in the dashboard.
+func GenericID(status int) string {
+	return fmt.Sprintf("server.generic.%d", status)
+}
+
+// KnownIDs lists every id above (used by the messages registry test).
+func KnownIDs() []string {
+	return []string{
+		IDNamespaceForbidden,
+		IDClusterForbidden,
+		IDNotFound,
+		IDAlreadyExists,
+		IDConflictRetry,
+		IDForbidden,
+		IDUnauthorized,
+		IDInvalid,
+		IDBadRequest,
+		IDEmptyBody,
+		IDInternal,
+		IDRemoteClusterNotImplemented,
+	}
+}
+
+// WantsProblem reports whether the request's Accept header asks for an
+// application/problem+json response. Every Accept value is parsed; a range
+// counts only when its media type is exactly application/problem+json
+// (wildcards never match) and its q parameter is above zero. A missing or
+// unparseable q means 1 and 0 respectively.
+func WantsProblem(r *http.Request) bool {
+	if r == nil {
+		return false
+	}
+	for _, header := range r.Header.Values("Accept") {
+		for _, rng := range strings.Split(header, ",") {
+			parts := strings.Split(rng, ";")
+			if !strings.EqualFold(strings.TrimSpace(parts[0]), problemJSON) {
+				continue
+			}
+			q := 1.0
+			for _, param := range parts[1:] {
+				key, value, ok := strings.Cut(param, "=")
+				if !ok || !strings.EqualFold(strings.TrimSpace(key), "q") {
+					continue
+				}
+				parsed, err := strconv.ParseFloat(strings.TrimSpace(value), 64)
+				if err != nil {
+					q = 0
+				} else {
+					q = parsed
+				}
+			}
+			if q > 0 {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// problemBody is the RFC 9457 document written for WantsProblem callers.
+// Field order is the wire order.
+type problemBody struct {
+	Type      string         `json:"type"`
+	Status    int            `json:"status"`
+	Title     string         `json:"title"`
+	Detail    string         `json:"detail"`
+	MessageID string         `json:"messageId"`
+	Args      map[string]any `json:"args"`
+}
+
+// writeError is the single response writer behind every helper here. It
+// writes the problem document for WantsProblem callers and otherwise the
+// byte-identical http.Error plain-text body.
+func writeError(w http.ResponseWriter, r *http.Request, status int, text, id string, args map[string]any) {
+	if !WantsProblem(r) {
+		http.Error(w, text, status)
+		return
+	}
+	if args == nil {
+		args = map[string]any{}
+	}
+	body := problemBody{
+		Type:      "about:blank",
+		Status:    status,
+		Title:     http.StatusText(status),
+		Detail:    strings.TrimSuffix(text, "\n"),
+		MessageID: id,
+		Args:      args,
+	}
+	var buf strings.Builder
+	enc := json.NewEncoder(&buf)
+	enc.SetEscapeHTML(false)
+	if err := enc.Encode(body); err != nil {
+		// The arguments could not be marshaled; fall back to the plain body
+		// rather than send a partial document.
+		http.Error(w, text, status)
+		return
+	}
+	w.Header().Set("Content-Type", problemJSON)
+	w.Header().Set("X-Content-Type-Options", "nosniff")
+	w.WriteHeader(status)
+	_, _ = io.WriteString(w, buf.String())
+}
+
 // WriteRemoteClusterNotImplemented answers 501 Not Implemented with
 // RemoteClusterNotImplemented as the body. It deliberately bypasses
 // WriteCode's >=500 masking (which replaces the body with the generic
@@ -42,30 +188,62 @@ func WriteRemoteClusterNotImplemented(w http.ResponseWriter) {
 // For a 4xx, err.Error() is echoed verbatim: by convention every existing
 // 4xx caller has already classified the condition and hand-built a message
 // safe to show the caller (e.g. "ref is required", "cluster already
-// exists"). For a >=500 status that contract does not hold — several
-// callers wrap a raw upstream error (e.g. a mod-registry GET failure) that
-// was never vetted for caller-safety, and a *url.Error embeds the full
-// request URL, query string included, which for a provider like Steam
-// carries an admin's API key. So >=500 never echoes err.Error(): the
-// generic http.StatusText for the code is written to the client, and the
-// real error is still logged in full server-side.
+// exists"). If err is a *Message, its English text, id and args are used
+// instead, so a problem-document caller also gets the registry id. A 4xx
+// without a *Message gets the id server.generic.<status>.
+//
+// For a >=500 status that contract does not hold — several callers wrap a
+// raw upstream error (e.g. a mod-registry GET failure) that was never
+// vetted for caller-safety, and a *url.Error embeds the full request URL,
+// query string included, which for a provider like Steam carries an
+// admin's API key. So >=500 never echoes err.Error(): the generic
+// http.StatusText for the code is written to the client, and the real
+// error is still logged in full server-side.
 func WriteCode(w http.ResponseWriter, req *http.Request, status int, err error) {
 	if status >= 500 {
 		slog.Error("handler error",
 			"method", req.Method, "path", req.URL.Path, "err", err)
-		http.Error(w, http.StatusText(status), status)
+		writeError(w, req, status, http.StatusText(status), GenericID(status), nil)
 		return
 	}
 	slog.Debug("handler client error",
 		"method", req.Method, "path", req.URL.Path, "status", status, "err", err)
-	http.Error(w, err.Error(), status)
+	var m *Message
+	if errors.As(err, &m) {
+		writeError(w, req, status, m.English, m.ID, m.Args)
+		return
+	}
+	writeError(w, req, status, err.Error(), GenericID(status), nil)
+}
+
+// WriteMessage writes a localizable Message. The English text is the
+// plain-text body, and a problem-document caller also gets m.ID and m.Args.
+// A nil message or a status of 0 becomes 500. For a status >=500 the body is
+// the generic http.StatusText, except for IDRemoteClusterNotImplemented,
+// whose fixed text is safe to show.
+func WriteMessage(w http.ResponseWriter, r *http.Request, m *Message) {
+	if m == nil {
+		m = &Message{ID: IDInternal, Status: http.StatusInternalServerError, English: "internal error"}
+	}
+	status := m.Status
+	if status == 0 {
+		status = http.StatusInternalServerError
+	}
+	text, id, args := m.English, m.ID, m.Args
+	if status >= 500 && m.ID != IDRemoteClusterNotImplemented {
+		text = http.StatusText(status)
+		id = GenericID(status)
+		args = nil
+	}
+	writeError(w, r, status, text, id, args)
 }
 
 // Write responds with the appropriate HTTP status for the given error
 // and a generic message. The actual error is logged at Error level so
-// operators can still debug.
+// operators can still debug. A *Message anywhere in the error chain is
+// rendered with its own status, id and arguments.
 func Write(w http.ResponseWriter, req *http.Request, err error) {
-	status, msg := classify(err)
+	status, msg, id, args := classify(err)
 	if status >= 500 {
 		slog.Error("handler error",
 			"method", req.Method, "path", req.URL.Path, "err", err)
@@ -73,47 +251,61 @@ func Write(w http.ResponseWriter, req *http.Request, err error) {
 		slog.Debug("handler client error",
 			"method", req.Method, "path", req.URL.Path, "status", status, "err", err)
 	}
-	http.Error(w, msg, status)
+	writeError(w, req, status, msg, id, args)
 }
 
-// classify returns (status, safeMessage) for a range of common errors.
-// The default is 500 "internal error" — never leak unknown errors.
-func classify(err error) (int, string) {
+// classify returns (status, safeMessage, messageID, args) for a range of
+// common errors. The default is 500 "internal error" — never leak unknown
+// errors.
+func classify(err error) (int, string, string, map[string]any) {
+	var m *Message
+	if errors.As(err, &m) {
+		if m.Status == 0 {
+			return http.StatusInternalServerError, "internal error", IDInternal, nil
+		}
+		if m.Status >= 500 && m.ID != IDRemoteClusterNotImplemented {
+			// Same masking as WriteCode and WriteMessage: a 5xx never
+			// echoes the message text or its arguments.
+			return m.Status, http.StatusText(m.Status), GenericID(m.Status), nil
+		}
+		return m.Status, m.English, m.ID, m.Args
+	}
 	switch {
 	case errors.Is(err, scope.ErrForbiddenNamespace):
-		return http.StatusForbidden, "namespace not permitted"
+		return http.StatusForbidden, "namespace not permitted", IDNamespaceForbidden, nil
 	case errors.Is(err, scope.ErrForbiddenCluster):
 		// 400, not 403: an unknown ?cluster= is a malformed request (like an
 		// unrecognized query param value), not an authorization decision —
 		// that mirrors rbac.Middleware's direct 400 for the same error.
-		return http.StatusBadRequest, "cluster not permitted"
+		return http.StatusBadRequest, "cluster not permitted", IDClusterForbidden, nil
 	case apierrors.IsNotFound(err):
-		return http.StatusNotFound, "not found"
+		return http.StatusNotFound, "not found", IDNotFound, nil
 	case errors.Is(err, db.ErrShareLinkNotFound):
-		return http.StatusNotFound, "not found"
+		return http.StatusNotFound, "not found", IDNotFound, nil
 	case apierrors.IsAlreadyExists(err):
-		return http.StatusConflict, "already exists"
+		return http.StatusConflict, "already exists", IDAlreadyExists, nil
 	case apierrors.IsConflict(err):
 		// A resourceVersion conflict is an expected, transient condition
 		// under concurrent writers (e.g. the operator's reconciler racing
 		// an API-initiated status update) — not a server bug. Surface it
 		// as a retryable 409 rather than falling through to the opaque
 		// 500 default below.
-		return http.StatusConflict, "conflict, retry"
+		return http.StatusConflict, "conflict, retry", IDConflictRetry, nil
 	case apierrors.IsForbidden(err):
-		return http.StatusForbidden, "forbidden"
+		return http.StatusForbidden, "forbidden", IDForbidden, nil
 	case apierrors.IsUnauthorized(err):
-		return http.StatusUnauthorized, "unauthorized"
+		return http.StatusUnauthorized, "unauthorized", IDUnauthorized, nil
 	case apierrors.IsInvalid(err):
 		// Validation errors are safe to surface — they describe the
 		// user's input, not server internals.
-		return http.StatusUnprocessableEntity, apiErrMessage(err)
+		msg := apiErrMessage(err)
+		return http.StatusUnprocessableEntity, msg, IDInvalid, map[string]any{"detail": msg}
 	case apierrors.IsBadRequest(err):
-		return http.StatusBadRequest, "bad request"
+		return http.StatusBadRequest, "bad request", IDBadRequest, nil
 	case errors.Is(err, io.EOF):
-		return http.StatusBadRequest, "empty body"
+		return http.StatusBadRequest, "empty body", IDEmptyBody, nil
 	}
-	return http.StatusInternalServerError, "internal error"
+	return http.StatusInternalServerError, "internal error", IDInternal, nil
 }
 
 func apiErrMessage(err error) string {
diff --git a/api/internal/httperr/httperr_test.go b/api/internal/httperr/httperr_test.go
index 67f9aba31..62f26d594 100644
--- a/api/internal/httperr/httperr_test.go
+++ b/api/internal/httperr/httperr_test.go
@@ -2,6 +2,7 @@ package httperr
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -152,3 +153,303 @@ func TestWrite_ConflictBodyDistinctFromAlreadyExists(t *testing.T) {
 		t.Fatalf("already-exists and conflict share the body %q", got)
 	}
 }
+
+// problemCase is one classify branch with the status, English text and
+// message id the response must carry.
+type problemCase struct {
+	name   string
+	err    error
+	status int
+	msg    string
+	id     string
+}
+
+func problemCases() []problemCase {
+	gr := schema.GroupResource{Resource: "x"}
+	invalid := &apierrors.StatusError{
+		ErrStatus: metav1.Status{
+			Status:  metav1.StatusFailure,
+			Reason:  metav1.StatusReasonInvalid,
+			Message: "name must be lowercase",
+			Code:    http.StatusUnprocessableEntity,
+		},
+	}
+	return []problemCase{
+		{"forbidden namespace", scope.ErrForbiddenNamespace, http.StatusForbidden, "namespace not permitted", IDNamespaceForbidden},
+		{"forbidden cluster", scope.ErrForbiddenCluster, http.StatusBadRequest, "cluster not permitted", IDClusterForbidden},
+		{"not found", apierrors.NewNotFound(gr, "n"), http.StatusNotFound, "not found", IDNotFound},
+		{"share link not found", fmt.Errorf("x: %w", db.ErrShareLinkNotFound), http.StatusNotFound, "not found", IDNotFound},
+		{"already exists", apierrors.NewAlreadyExists(gr, "n"), http.StatusConflict, "already exists", IDAlreadyExists},
+		{"resourceVersion conflict", apierrors.NewConflict(gr, "n", errors.New("modified")), http.StatusConflict, "conflict, retry", IDConflictRetry},
+		{"forbidden", apierrors.NewForbidden(gr, "n", errors.New("rbac")), http.StatusForbidden, "forbidden", IDForbidden},
+		{"unauthorized", apierrors.NewUnauthorized("nope"), http.StatusUnauthorized, "unauthorized", IDUnauthorized},
+		{"invalid", invalid, http.StatusUnprocessableEntity, "name must be lowercase", IDInvalid},
+		{"bad request", apierrors.NewBadRequest("nope"), http.StatusBadRequest, "bad request", IDBadRequest},
+		{"empty body (io.EOF)", io.EOF, http.StatusBadRequest, "empty body", IDEmptyBody},
+		{"unknown", errors.New("mystery"), http.StatusInternalServerError, "internal error", IDInternal},
+		{"registry message", fmt.Errorf("wrap: %w", &Message{ID: "x.teapot", Status: http.StatusTeapot, English: "short and stout"}), http.StatusTeapot, "short and stout", "x.teapot"},
+	}
+}
+
+// acceptReq is newReq with an Accept header set.
+func acceptReq(accept string) *http.Request {
+	r := newReq()
+	r.Header.Set("Accept", accept)
+	return r
+}
+
+// TestWrite_PlainBodyByteIdentical pins that every response that does not ask
+// for a problem document is exactly what http.Error wrote before this change.
+func TestWrite_PlainBodyByteIdentical(t *testing.T) {
+	accepts := []string{"", "*/*", "application/problem+json;q=0"}
+	for _, tc := range problemCases() {
+		for _, accept := range accepts {
+			t.Run(fmt.Sprintf("%s/accept=%q", tc.name, accept), func(t *testing.T) {
+				rr := httptest.NewRecorder()
+				Write(rr, acceptReq(accept), tc.err)
+
+				want := httptest.NewRecorder()
+				http.Error(want, tc.msg, tc.status)
+
+				if rr.Code != want.Code {
+					t.Fatalf("code = %d, want %d", rr.Code, want.Code)
+				}
+				if rr.Body.String() != want.Body.String() {
+					t.Fatalf("body = %q, want %q", rr.Body.String(), want.Body.String())
+				}
+				if got, want := rr.Header().Get("Content-Type"), "text/plain; charset=utf-8"; got != want {
+					t.Fatalf("Content-Type = %q, want %q", got, want)
+				}
+				if got, want := rr.Header().Get("X-Content-Type-Options"), "nosniff"; got != want {
+					t.Fatalf("X-Content-Type-Options = %q, want %q", got, want)
+				}
+			})
+		}
+	}
+}
+
+// decodedProblem mirrors the problem document fields the tests check.
+type decodedProblem struct {
+	Type      string         `json:"type"`
+	Status    int            `json:"status"`
+	Title     string         `json:"title"`
+	Detail    string         `json:"detail"`
+	MessageID string         `json:"messageId"`
+	Args      map[string]any `json:"args"`
+}
+
+// TestWrite_ProblemDocument checks the problem response for every classify
+// branch when the caller accepts application/problem+json.
+func TestWrite_ProblemDocument(t *testing.T) {
+	for _, tc := range problemCases() {
+		t.Run(tc.name, func(t *testing.T) {
+			rr := httptest.NewRecorder()
+			Write(rr, acceptReq("application/json, application/problem+json"), tc.err)
+
+			if rr.Code != tc.status {
+				t.Fatalf("code = %d, want %d", rr.Code, tc.status)
+			}
+			if got := rr.Header().Get("Content-Type"); got != "application/problem+json" {
+				t.Fatalf("Content-Type = %q", got)
+			}
+			if got := rr.Header().Get("X-Content-Type-Options"); got != "nosniff" {
+				t.Fatalf("X-Content-Type-Options = %q", got)
+			}
+			body := rr.Body.String()
+			if strings.Count(body, "\n") != 1 || !strings.HasSuffix(body, "\n") {
+				t.Fatalf("body must be one JSON line plus newline: %q", body)
+			}
+			var doc decodedProblem
+			if err := json.Unmarshal([]byte(body), &doc); err != nil {
+				t.Fatalf("decode %q: %v", body, err)
+			}
+			if doc.Type != "about:blank" {
+				t.Fatalf("type = %q", doc.Type)
+			}
+			if doc.Status != tc.status {
+				t.Fatalf("status = %d, want %d", doc.Status, tc.status)
+			}
+			if doc.Title != http.StatusText(tc.status) {
+				t.Fatalf("title = %q, want %q", doc.Title, http.StatusText(tc.status))
+			}
+			if doc.Detail != tc.msg {
+				t.Fatalf("detail = %q, want %q", doc.Detail, tc.msg)
+			}
+			if doc.MessageID != tc.id {
+				t.Fatalf("messageId = %q, want %q", doc.MessageID, tc.id)
+			}
+			if doc.Args == nil {
+				t.Fatalf("args must be an object, got null in %q", body)
+			}
+			if tc.id == IDInvalid && doc.Args["detail"] != tc.msg {
+				t.Fatalf("args = %v, want detail %q", doc.Args, tc.msg)
+			}
+		})
+	}
+}
+
+// TestWriteCode_ProblemDocument4xxUsesErrText checks a hand-built 4xx on a
+// problem-document caller: the text is the error's, the id is the generic one.
+func TestWriteCode_ProblemDocument4xxUsesErrText(t *testing.T) {
+	rr := httptest.NewRecorder()
+	WriteCode(rr, acceptReq("application/problem+json"), http.StatusBadRequest, errors.New("ref is required"))
+	var doc decodedProblem
+	if err := json.Unmarshal(rr.Body.Bytes(), &doc); err != nil {
+		t.Fatalf("decode %q: %v", rr.Body.String(), err)
+	}
+	if doc.MessageID != "server.generic.400" {
+		t.Fatalf("messageId = %q, want server.generic.400", doc.MessageID)
+	}
+	if doc.Detail != "ref is required" {
+		t.Fatalf("detail = %q", doc.Detail)
+	}
+}
+
+// TestWriteCode_ProblemDocument5xxNeverLeaks checks a >=500 WriteCode on a
+// problem-document caller: the detail is the status text, never the error.
+func TestWriteCode_ProblemDocument5xxNeverLeaks(t *testing.T) {
+	rr := httptest.NewRecorder()
+	WriteCode(rr, acceptReq("application/problem+json"), http.StatusInternalServerError,
+		errors.New("boom with s3cret-token"))
+	if strings.Contains(rr.Body.String(), "s3cret-token") {
+		t.Fatalf("body leaks the raw error: %q", rr.Body.String())
+	}
+	var doc decodedProblem
+	if err := json.Unmarshal(rr.Body.Bytes(), &doc); err != nil {
+		t.Fatalf("decode %q: %v", rr.Body.String(), err)
+	}
+	if doc.Detail != "Internal Server Error" {
+		t.Fatalf("detail = %q, want the status text", doc.Detail)
+	}
+	if doc.MessageID != "server.generic.500" {
+		t.Fatalf("messageId = %q, want server.generic.500", doc.MessageID)
+	}
+}
+
+// TestWriteCode_MessageKeepsIDAndArgs checks that a *Message in a 4xx
+// WriteCode keeps its id and args for a problem-document caller.
+func TestWriteCode_MessageKeepsIDAndArgs(t *testing.T) {
+	m := &Message{ID: "x.custom", Status: http.StatusConflict, English: "custom text", Args: map[string]any{"n": 3}}
+	rr := httptest.NewRecorder()
+	WriteCode(rr, acceptReq("application/problem+json"), http.StatusConflict, m)
+	var doc decodedProblem
+	if err := json.Unmarshal(rr.Body.Bytes(), &doc); err != nil {
+		t.Fatalf("decode %q: %v", rr.Body.String(), err)
+	}
+	if doc.MessageID != "x.custom" || doc.Detail != "custom text" || doc.Args["n"] != float64(3) {
+		t.Fatalf("doc = %+v", doc)
+	}
+}
+
+// TestWriteMessage_Custom covers the custom-message path: the status, the
+// plain body, the problem document, and the >=500 masking rule.
+func TestWriteMessage_Custom(t *testing.T) {
+	m := &Message{ID: "x.custom", Status: http.StatusConflict, English: "custom text", Args: map[string]any{"n": 3}}
+
+	rr := httptest.NewRecorder()
+	WriteMessage(rr, acceptReq(""), m)
+	if rr.Code != http.StatusConflict || rr.Body.String() != "custom text\n" {
+		t.Fatalf("plain: code=%d body=%q", rr.Code, rr.Body.String())
+	}
+
+	rr2 := httptest.NewRecorder()
+	WriteMessage(rr2, acceptReq("application/problem+json"), m)
+	var doc decodedProblem
+	if err := json.Unmarshal(rr2.Body.Bytes(), &doc); err != nil {
+		t.Fatalf("decode %q: %v", rr2.Body.String(), err)
+	}
+	if rr2.Code != http.StatusConflict || doc.MessageID != "x.custom" || doc.Detail != "custom text" || doc.Args["n"] != float64(3) {
+		t.Fatalf("problem: code=%d doc=%+v", rr2.Code, doc)
+	}
+}
+
+func TestWriteMessage_ServerErrorMasked(t *testing.T) {
+	m := &Message{ID: "x.boom", Status: http.StatusServiceUnavailable, English: "secret upstream text"}
+	rr := httptest.NewRecorder()
+	WriteMessage(rr, acceptReq(""), m)
+	if rr.Code != http.StatusServiceUnavailable {
+		t.Fatalf("code = %d", rr.Code)
+	}
+	if rr.Body.String() != "Service Unavailable\n" {
+		t.Fatalf("body = %q, want the status text", rr.Body.String())
+	}
+}
+
+func TestWriteMessage_RemoteClusterKeepsText(t *testing.T) {
+	m := &Message{ID: IDRemoteClusterNotImplemented, Status: http.StatusNotImplemented, English: RemoteClusterNotImplemented}
+	rr := httptest.NewRecorder()
+	WriteMessage(rr, acceptReq(""), m)
+	if rr.Code != http.StatusNotImplemented {
+		t.Fatalf("code = %d", rr.Code)
+	}
+	if rr.Body.String() != RemoteClusterNotImplemented+"\n" {
+		t.Fatalf("body = %q", rr.Body.String())
+	}
+}
+
+func TestWriteMessage_NilAndZeroStatusAre500(t *testing.T) {
+	rr := httptest.NewRecorder()
+	WriteMessage(rr, acceptReq(""), nil)
+	if rr.Code != http.StatusInternalServerError {
+		t.Fatalf("nil message: code = %d", rr.Code)
+	}
+	rr2 := httptest.NewRecorder()
+	WriteMessage(rr2, acceptReq(""), &Message{ID: "x.zero", English: "zero status"})
+	if rr2.Code != http.StatusInternalServerError {
+		t.Fatalf("zero status: code = %d", rr2.Code)
+	}
+}
+
+// TestWrite_WrappedMessage checks errors.As through Write with a wrapped
+// *Message: the status, the plain text and the problem id all come from it.
+func TestWrite_WrappedMessage(t *testing.T) {
+	m := &Message{ID: "x.field", Status: http.StatusUnprocessableEntity, English: "bad field", Args: map[string]any{"detail": "bad field"}}
+	err := fmt.Errorf("x: %w", m)
+
+	rr := httptest.NewRecorder()
+	Write(rr, acceptReq(""), err)
+	if rr.Code != http.StatusUnprocessableEntity || rr.Body.String() != "bad field\n" {
+		t.Fatalf("plain: code=%d body=%q", rr.Code, rr.Body.String())
+	}
+
+	rr2 := httptest.NewRecorder()
+	Write(rr2, acceptReq("application/problem+json"), err)
+	var doc decodedProblem
+	if err := json.Unmarshal(rr2.Body.Bytes(), &doc); err != nil {
+		t.Fatalf("decode %q: %v", rr2.Body.String(), err)
+	}
+	if doc.MessageID != "x.field" || doc.Args["detail"] != "bad field" {
+		t.Fatalf("doc = %+v", doc)
+	}
+}
+
+// TestWantsProblem covers the Accept header negotiation.
+func TestWantsProblem(t *testing.T) {
+	cases := []struct {
+		name   string
+		accept string
+		want   bool
+	}{
+		{"empty", "", false},
+		{"any type", "*/*", false},
+		{"application wildcard", "application/*", false},
+		{"json only", "application/json", false},
+		{"problem json", "application/problem+json", true},
+		{"mixed case", "Application/Problem+JSON", true},
+		{"q zero", "application/problem+json;q=0", false},
+		{"q half", "application/problem+json; q=0.5", true},
+		{"listed after text", "text/html, application/problem+json;q=0.1", true},
+		{"bad q", "application/problem+json;q=bogus", false},
+		{"json q zero then problem", "application/json;q=0, application/problem+json", true},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := WantsProblem(acceptReq(tc.accept)); got != tc.want {
+				t.Fatalf("WantsProblem(%q) = %v, want %v", tc.accept, got, tc.want)
+			}
+		})
+	}
+	if WantsProblem(nil) {
+		t.Fatal("WantsProblem(nil) = true")
+	}
+}
diff --git a/api/internal/messages/entries_server.go b/api/internal/messages/entries_server.go
new file mode 100644
index 000000000..a78106cf6
--- /dev/null
+++ b/api/internal/messages/entries_server.go
@@ -0,0 +1,362 @@
+package messages
+
+import "net/http"
+
+// serverEntries holds the registry messages for API handlers migrated from
+// plain http.Error text to localizable messages (US5).
+var serverEntries = []Entry{
+	{
+		ID:          "server.auth.csrf_mismatch",
+		English:     "csrf mismatch",
+		Description: "API error from the session layer (sessions.go:Authenticate).",
+		Status:      http.StatusForbidden,
+	},
+	{
+		ID:          "server.auth_providers.client_secret_required",
+		English:     "clientSecret is required",
+		Description: "API error from the auth provider credentials API (auth_provider_secret.go:put).",
+		Status:      http.StatusUnprocessableEntity,
+	},
+	{
+		ID:          "server.common.invalid_json",
+		English:     "invalid json",
+		Description: "API error when a request body is not valid JSON.",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.common.namespace_not_permitted",
+		English:     "namespace not permitted",
+		Description: "API error when the caller's role does not cover the requested namespace (400 form, returned by the permission check and the role-binding API).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.common.too_many_requests",
+		English:     "too many requests",
+		Description: "API error when a signed-in user sends requests faster than the per-user rate limit allows; retry later.",
+		Status:      http.StatusTooManyRequests,
+	},
+	{
+		ID:          "server.common.unauthenticated",
+		English:     "unauthenticated",
+		Description: "API error when a route that needs a signed-in user is called without a valid session.",
+		Status:      http.StatusUnauthorized,
+	},
+	{
+		ID:          "server.common.user_not_found",
+		English:     "user not found",
+		Description: "API error when the user named in the request does not exist.",
+		Status:      http.StatusNotFound,
+	},
+	{
+		ID:          "server.config.read_body",
+		English:     "read body",
+		Description: "API error from the admin config API (config.go:put).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.config.unknown_section",
+		English:     "unknown section",
+		Description: "API error from the admin config API (config.go:put).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.generic.415",
+		English:     "The request type is not supported.",
+		Description: "Generic sentence shown before the detail text for an HTTP 415 response.",
+		Status:      http.StatusUnsupportedMediaType,
+	},
+	{
+		ID:          "server.lifecycle.confirmation_mismatch",
+		English:     "confirmation does not match server name",
+		Description: "API error from the server lifecycle API (lifecycle.go:wipeDataHandler).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.lifecycle.new_name_required",
+		English:     "newName required",
+		Description: "API error from the server lifecycle API (lifecycle.go:cloneHandler).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.notifications.sink_name_not_dns_label",
+		English:     "sink name must be a DNS label (lowercase, digits, hyphens)",
+		Description: "API error from the notification sinks API (notifications.go:deleteSecret, notifications.go:putSecret).",
+		Status:      http.StatusUnprocessableEntity,
+	},
+	{
+		ID:          "server.ownership.invalid_request",
+		English:     "invalid request",
+		Description: "API error from the server ownership API (ownership.go:setCollaborators).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.ownership.user_id_required",
+		English:     "userId required",
+		Description: "API error from the server ownership API (ownership.go:transfer).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.ownership.user_not_found_400",
+		English:     "user not found",
+		Description: "API error from the server ownership API (ownership.go:setCollaborators).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.registry.api_key_required",
+		English:     "apiKey is required",
+		Description: "API error from the mod-registry credentials API (registry_secret.go:put).",
+		Status:      http.StatusUnprocessableEntity,
+	},
+	{
+		ID:          "server.roles.admin_not_editable",
+		English:     "the admin role cannot be edited",
+		Description: "API error from the roles API (roles.go:update).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.roles.builtin_not_deletable",
+		English:     "built-in roles cannot be deleted",
+		Description: "API error from the roles API (roles.go:del).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.roles.invalid_role_name",
+		English:     "invalid role name",
+		Description: "API error from the roles API (roles.go:create).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.roles.remote_bindings_block_control_plane",
+		English:     "remove remote cluster-wide bindings before adding control-plane permissions",
+		Description: "API error from the roles API (roles.go:update).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.roles.role_already_exists",
+		English:     "role already exists",
+		Description: "API error from the roles API (roles.go:create).",
+		Status:      http.StatusConflict,
+	},
+	{
+		ID:          "server.roles.role_in_use",
+		English:     "role is assigned to one or more users",
+		Description: "API error from the roles API (roles.go:del).",
+		Status:      http.StatusConflict,
+	},
+	{
+		ID:          "server.roles.role_not_found",
+		English:     "role not found",
+		Description: "API error from the roles API (roles.go:del, roles.go:update).",
+		Status:      http.StatusNotFound,
+	},
+	{
+		ID:          "server.shares.expires_at_in_past",
+		English:     "expiresAt must be in the future",
+		Description: "API error from the share-links API (shares.go:createShareHandler).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.shares.expiry_mutually_exclusive",
+		English:     "expiresAt and neverExpires are mutually exclusive",
+		Description: "API error from the share-links API (shares.go:createShareHandler).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.shares.expiry_required",
+		English:     "must specify exactly one of expiresAt or neverExpires (or the deprecated expiresIn)",
+		Description: "API error from the share-links API (shares.go:createShareHandler).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.shares.invalid_expires_at",
+		English:     "invalid expiresAt: must be RFC3339",
+		Description: "API error from the share-links API (shares.go:createShareHandler).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.shares.invalid_expires_in",
+		English:     "invalid expiresIn",
+		Description: "API error from the share-links API (shares.go:createShareHandler).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.telemetry.invalid_notice_action",
+		English:     "action must be one of seen|keep|extended-off|all-off",
+		Description: "API error from the telemetry API (telemetry.go:postNotice). Quoted words and tokens in the text are API keywords; keep them as written.",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.telemetry.notice_not_pending",
+		English:     "telemetry notice is not pending",
+		Description: "API error from the telemetry API (telemetry.go:postNotice).",
+		Status:      http.StatusConflict,
+	},
+	{
+		ID:          "server.tunnel.credentials_in_use",
+		English:     "cannot delete tunnel credentials while tunnel is enabled; disable the tunnel first or use PUT to rotate credentials",
+		Description: "API error from the tunnel credentials API (tunnelcreds.go:delete).",
+		Status:      http.StatusConflict,
+	},
+	{
+		ID:          "server.tunnel.invalid_request_body",
+		English:     "invalid request body",
+		Description: "API error from the tunnel credentials API (tunnelcreds.go:put).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.tunnel.secret_not_owned_conflict",
+		English:     "conflict: existing secret is not owned by this server",
+		Description: "API error from the tunnel credentials API (tunnelcreds.go:put).",
+		Status:      http.StatusConflict,
+	},
+	{
+		ID:          "server.tunnel.secret_not_owned_forbidden",
+		English:     "forbidden: cannot delete secret not owned by this server",
+		Description: "API error from the tunnel credentials API (tunnelcreds.go:delete).",
+		Status:      http.StatusForbidden,
+	},
+	{
+		ID:          "server.users.appearance_mode_invalid",
+		English:     "appearanceMode must be \"light\", \"dark\" or \"system\"",
+		Description: "API error from the users API (users.go:putPreferences, users.go:resetPreferences). Quoted words and tokens in the text are API keywords; keep them as written.",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.appearance_mode_required",
+		English:     "appearanceMode is required",
+		Description: "API error from the users API (users.go:putPreferences).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.bad_id",
+		English:     "bad id",
+		Description: "API error from the users API (users.go:addBinding, users.go:del, users.go:deleteBinding, users.go:listBindings, users.go:resetPassword, users.go:update).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.binding_already_exists",
+		English:     "binding already exists",
+		Description: "API error from the users API (users.go:addBinding).",
+		Status:      http.StatusConflict,
+	},
+	{
+		ID:          "server.users.binding_not_found",
+		English:     "binding not found",
+		Description: "API error from the users API (users.go:deleteBinding).",
+		Status:      http.StatusNotFound,
+	},
+	{
+		ID:          "server.users.cannot_delete_last_manager",
+		English:     "cannot delete the last user who can manage users",
+		Description: "API error from the users API (users.go:del).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.cannot_delete_self",
+		English:     "cannot delete self",
+		Description: "API error from the users API (users.go:del).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.cannot_demote_last_manager",
+		English:     "cannot demote the last user who can manage users",
+		Description: "API error from the users API (users.go:update).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.cannot_remove_own_management",
+		English:     "cannot remove your own user-management access",
+		Description: "API error from the users API (users.go:update).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.cluster_role_is_primary",
+		English:     "the cluster-wide role is managed via the primary role",
+		Description: "API error from the users API (users.go:deleteBinding).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.custom_accent_invalid",
+		English:     "customColors.accent must be a #RRGGBB hex color",
+		Description: "API error from the users API (users.go:putPreferences). Quoted words and tokens in the text are API keywords; keep them as written.",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.custom_css_enabled_required",
+		English:     "customCssEnabled is required",
+		Description: "API error from the users API (users.go:putPreferences).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.custom_surface_invalid",
+		English:     "customColors.surface must be a #RRGGBB hex color",
+		Description: "API error from the users API (users.go:putPreferences). Quoted words and tokens in the text are API keywords; keep them as written.",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.invalid_email",
+		English:     "invalid email",
+		Description: "API error from the users API (users.go:create, users.go:update).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.invalid_role",
+		English:     "invalid role",
+		Description: "API error from the users API (users.go:addBinding, users.go:create, users.go:update).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.invalid_username",
+		English:     "invalid username",
+		Description: "API error from the users API (users.go:create).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.password_too_short",
+		English:     "password too short",
+		Description: "API error from the users API (users.go:create, users.go:resetPassword).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.preset_id_invalid",
+		English:     "presetId must be \"pink\" or \"legacy\"",
+		Description: "API error from the users API (users.go:putPreferences, users.go:resetPreferences). Quoted words and tokens in the text are API keywords; keep them as written.",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.preset_id_required",
+		English:     "presetId is required",
+		Description: "API error from the users API (users.go:putPreferences).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.remote_binding_not_removable",
+		English:     "remote control-plane bindings cannot be removed through supplemental grants",
+		Description: "API error from the users API (users.go:deleteBinding).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.remote_role_scope_limited",
+		English:     "remote cluster-wide roles may grant only cluster:read and namespaced permissions",
+		Description: "API error from the users API (users.go:addBinding).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.theme_type_invalid",
+		English:     "themeType must be \"preset\" or \"custom_colors\"",
+		Description: "API error from the users API (users.go:putPreferences). Quoted words and tokens in the text are API keywords; keep them as written.",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.users.theme_type_required",
+		English:     "themeType is required",
+		Description: "API error from the users API (users.go:putPreferences).",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.ws.invalid_server_name",
+		English:     "invalid server name",
+		Description: "API error from the console and log WebSocket routes (attach.go:handle, podlogs.go:handle).",
+		Status:      http.StatusBadRequest,
+	},
+}
diff --git a/api/internal/messages/export.go b/api/internal/messages/export.go
new file mode 100644
index 000000000..444e0f48b
--- /dev/null
+++ b/api/internal/messages/export.go
@@ -0,0 +1,28 @@
+package messages
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"slices"
+	"strings"
+)
+
+// ExportJSON writes the registry as a JSON array sorted by id, with
+// two-space indentation and a trailing newline. The extra entries (for
+// example the notify.* text owned by another package) are written alongside
+// the registry's own. The i18n tooling reads this output to sync the server.*
+// and notify.* entries of the English reference pack.
+func ExportJSON(w io.Writer, extra ...Entry) error {
+	all := append(All(), extra...)
+	slices.SortFunc(all, func(a, b Entry) int {
+		return strings.Compare(string(a.ID), string(b.ID))
+	})
+	enc := json.NewEncoder(w)
+	enc.SetEscapeHTML(false)
+	enc.SetIndent("", "  ")
+	if err := enc.Encode(all); err != nil {
+		return fmt.Errorf("messages: export json: %w", err)
+	}
+	return nil
+}
diff --git a/api/internal/messages/messages.go b/api/internal/messages/messages.go
new file mode 100644
index 000000000..40f96e104
--- /dev/null
+++ b/api/internal/messages/messages.go
@@ -0,0 +1,263 @@
+// Package messages is the registry of localizable API error messages.
+//
+// Each entry pairs a stable id with its English ICU MessageFormat text, a
+// translator note and the default HTTP status. httperr.Message values built
+// with New carry the id and arguments in problem responses, so the dashboard
+// can localize them. The English text stays the plain-text body, unchanged.
+//
+// The registry is compile-time constant data. Every English text is parsed
+// once at package init, and a parse failure panics, because a malformed
+// entry is a programming error that the messages tests guard against.
+package messages
+
+import (
+	"fmt"
+	"net/http"
+	"slices"
+	"strings"
+
+	"golang.org/x/text/language"
+
+	"github.com/GameplanePanel/gameplane/api/internal/httperr"
+	"github.com/GameplanePanel/gameplane/i18n/icu"
+)
+
+// ID is a registry message id, for example "server.not_found".
+type ID string
+
+// Entry is one registry message.
+type Entry struct {
+	ID          ID     `json:"id"`
+	English     string `json:"english"`     // ICU MessageFormat
+	Description string `json:"description"` // translator note
+	Status      int    `json:"-"`           // default HTTP status for New
+}
+
+// entries is the registry. Each English text is byte-identical to the
+// message the API has always returned.
+var entries = []Entry{
+	{
+		ID:          httperr.IDNamespaceForbidden,
+		English:     "namespace not permitted",
+		Description: "API error when the user's role does not cover the requested namespace.",
+		Status:      http.StatusForbidden,
+	},
+	{
+		ID:          httperr.IDClusterForbidden,
+		English:     "cluster not permitted",
+		Description: "API error when the ?cluster= query value names a cluster the caller may not use or that is unknown.",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          httperr.IDNotFound,
+		English:     "not found",
+		Description: "API error when the requested resource does not exist.",
+		Status:      http.StatusNotFound,
+	},
+	{
+		ID:          httperr.IDAlreadyExists,
+		English:     "already exists",
+		Description: "API error when creating a resource whose name is already taken.",
+		Status:      http.StatusConflict,
+	},
+	{
+		ID:          httperr.IDConflictRetry,
+		English:     "conflict, retry",
+		Description: "API error when a concurrent write changed the resource; the caller should re-read and retry.",
+		Status:      http.StatusConflict,
+	},
+	{
+		ID:          httperr.IDForbidden,
+		English:     "forbidden",
+		Description: "API error when the caller, or the API's service identity in Kubernetes, is not allowed to perform the operation.",
+		Status:      http.StatusForbidden,
+	},
+	{
+		ID:          httperr.IDUnauthorized,
+		English:     "unauthorized",
+		Description: "API error when the request carries no valid credentials, or Kubernetes rejects the credentials used for the operation.",
+		Status:      http.StatusUnauthorized,
+	},
+	{
+		ID:          httperr.IDInvalid,
+		English:     "{detail}",
+		Description: "API validation error. The argument detail is the validation message from Kubernetes, in English, and describes the caller's input.",
+		Status:      http.StatusUnprocessableEntity,
+	},
+	{
+		ID:          httperr.IDBadRequest,
+		English:     "bad request",
+		Description: "API error for a malformed request that does not fit a more specific message.",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          httperr.IDEmptyBody,
+		English:     "empty body",
+		Description: "API error when a route that expects a JSON body receives none.",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          httperr.IDInternal,
+		English:     "internal error",
+		Description: "API error for an unexpected server failure. The real error is logged on the server only.",
+		Status:      http.StatusInternalServerError,
+	},
+	{
+		ID:          httperr.IDRemoteClusterNotImplemented,
+		English:     httperr.RemoteClusterNotImplemented,
+		Description: "API response for a home-cluster-only route called with a ?cluster= value that names another cluster. No cross-cluster agent exists yet.",
+		Status:      http.StatusNotImplemented,
+	},
+	{
+		ID:          "server.auth.invalid_credentials",
+		English:     "invalid credentials",
+		Description: "Login error. It is generic on purpose, so it never reveals whether an account exists.",
+		Status:      http.StatusUnauthorized,
+	},
+	{
+		ID:          "server.generic.400",
+		English:     "The request was not accepted.",
+		Description: "Generic sentence shown before the detail text for an HTTP 400 response.",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.generic.401",
+		English:     "You are not signed in.",
+		Description: "Generic sentence shown before the detail text for an HTTP 401 response.",
+		Status:      http.StatusUnauthorized,
+	},
+	{
+		ID:          "server.generic.403",
+		English:     "You do not have permission to do this.",
+		Description: "Generic sentence shown before the detail text for an HTTP 403 response.",
+		Status:      http.StatusForbidden,
+	},
+	{
+		ID:          "server.generic.404",
+		English:     "The requested item was not found.",
+		Description: "Generic sentence shown before the detail text for an HTTP 404 response.",
+		Status:      http.StatusNotFound,
+	},
+	{
+		ID:          "server.generic.409",
+		English:     "The request conflicts with the current state.",
+		Description: "Generic sentence shown before the detail text for an HTTP 409 response.",
+		Status:      http.StatusConflict,
+	},
+	{
+		ID:          "server.generic.413",
+		English:     "The request is too large.",
+		Description: "Generic sentence shown before the detail text for an HTTP 413 response.",
+		Status:      http.StatusRequestEntityTooLarge,
+	},
+	{
+		ID:          "server.generic.422",
+		English:     "The request contains invalid values.",
+		Description: "Generic sentence shown before the detail text for an HTTP 422 response.",
+		Status:      http.StatusUnprocessableEntity,
+	},
+	{
+		ID:          "server.generic.429",
+		English:     "Too many requests. Please wait and try again.",
+		Description: "Generic sentence shown before the detail text for an HTTP 429 response.",
+		Status:      http.StatusTooManyRequests,
+	},
+	{
+		ID:          "server.generic.500",
+		English:     "The server hit an internal error.",
+		Description: "Generic sentence shown before the detail text for an HTTP 500 response.",
+		Status:      http.StatusInternalServerError,
+	},
+	{
+		ID:          "server.generic.501",
+		English:     "This is not supported here.",
+		Description: "Generic sentence shown before the detail text for an HTTP 501 response.",
+		Status:      http.StatusNotImplemented,
+	},
+	{
+		ID:          "server.generic.502",
+		English:     "An upstream service returned an error.",
+		Description: "Generic sentence shown before the detail text for an HTTP 502 response.",
+		Status:      http.StatusBadGateway,
+	},
+	{
+		ID:          "server.generic.503",
+		English:     "The service is temporarily unavailable.",
+		Description: "Generic sentence shown before the detail text for an HTTP 503 response.",
+		Status:      http.StatusServiceUnavailable,
+	},
+	{
+		ID:          "server.i18n.unknown_language",
+		English:     "unknown language: {language}",
+		Description: "Shown when a user picks a language this release does not offer. language = the language tag that was sent.",
+		Status:      http.StatusBadRequest,
+	},
+	{
+		ID:          "server.i18n.unlisted_language",
+		English:     "language is not available: {language}",
+		Description: "Shown when an admin picks an instance default language that is not offered (missing or below the completeness threshold). language = the tag.",
+		Status:      http.StatusBadRequest,
+	},
+}
+
+// parsedEntry is a registry entry with its English text parsed once.
+type parsedEntry struct {
+	entry Entry
+	msg   icu.Message
+}
+
+var (
+	// byID indexes the registry by id.
+	byID map[ID]parsedEntry
+	// sorted is the registry sorted by id, returned by All.
+	sorted []Entry
+)
+
+func init() {
+	all := slices.Concat(entries, serverEntries)
+	byID = make(map[ID]parsedEntry, len(all))
+	for _, e := range all {
+		if _, dup := byID[e.ID]; dup {
+			panic(fmt.Sprintf("messages: duplicate id %q", e.ID))
+		}
+		msg, err := icu.Parse(e.English)
+		if err != nil {
+			panic(fmt.Sprintf("messages: entry %q: parse English: %v", e.ID, err))
+		}
+		byID[e.ID] = parsedEntry{entry: e, msg: msg}
+	}
+	sorted = slices.Clone(all)
+	slices.SortFunc(sorted, func(a, b Entry) int {
+		return strings.Compare(string(a.ID), string(b.ID))
+	})
+}
+
+// All returns a copy of every registry entry, sorted by ID.
+func All() []Entry {
+	return slices.Clone(sorted)
+}
+
+// Lookup returns the registry entry for id.
+func Lookup(id ID) (Entry, bool) {
+	p, ok := byID[id]
+	if !ok {
+		return Entry{}, false
+	}
+	return p.entry, true
+}
+
+// New builds a localizable error for id. Its English text is the entry's
+// ICU text rendered with args. An unknown id yields a 500 "internal error"
+// that keeps the requested id, so the mistake stays visible in responses.
+func New(id ID, args map[string]any) *httperr.Message {
+	p, ok := byID[id]
+	if !ok {
+		return &httperr.Message{ID: string(id), Status: http.StatusInternalServerError, English: "internal error"}
+	}
+	return &httperr.Message{
+		ID:      string(id),
+		Args:    args,
+		Status:  p.entry.Status,
+		English: icu.Format(p.msg, language.English, args),
+	}
+}
diff --git a/api/internal/messages/messages_test.go b/api/internal/messages/messages_test.go
new file mode 100644
index 000000000..ba9b089c9
--- /dev/null
+++ b/api/internal/messages/messages_test.go
@@ -0,0 +1,146 @@
+package messages
+
+import (
+	"bytes"
+	"encoding/json"
+	"net/http"
+	"strings"
+	"testing"
+
+	"github.com/GameplanePanel/gameplane/api/internal/httperr"
+)
+
+// genericCodes are the HTTP statuses that have a server.generic.<code> entry.
+var genericCodes = []int{400, 401, 403, 404, 409, 413, 422, 429, 500, 501, 502, 503}
+
+func TestKnownIDsAreRegistered(t *testing.T) {
+	for _, id := range httperr.KnownIDs() {
+		if _, ok := Lookup(ID(id)); !ok {
+			t.Errorf("httperr id %q is not registered", id)
+		}
+	}
+}
+
+func TestGenericIDsAreRegistered(t *testing.T) {
+	for _, code := range genericCodes {
+		id := ID(httperr.GenericID(code))
+		e, ok := Lookup(id)
+		if !ok {
+			t.Errorf("generic id %q is not registered", id)
+			continue
+		}
+		if e.Status != code {
+			t.Errorf("%q status = %d, want %d", id, e.Status, code)
+		}
+	}
+}
+
+func TestNewRendersEnglishWithArgs(t *testing.T) {
+	m := New(ID(httperr.IDInvalid), map[string]any{"detail": "name must be lowercase"})
+	if m.English != "name must be lowercase" {
+		t.Fatalf("English = %q", m.English)
+	}
+	if m.ID != httperr.IDInvalid {
+		t.Fatalf("ID = %q", m.ID)
+	}
+	if m.Status != http.StatusUnprocessableEntity {
+		t.Fatalf("Status = %d", m.Status)
+	}
+	if m.Args["detail"] != "name must be lowercase" {
+		t.Fatalf("Args = %v", m.Args)
+	}
+}
+
+func TestNewPlainEntryStatus(t *testing.T) {
+	m := New(ID(httperr.IDNotFound), nil)
+	if m.English != "not found" || m.Status != http.StatusNotFound {
+		t.Fatalf("got English=%q Status=%d", m.English, m.Status)
+	}
+}
+
+func TestNewUnknownIDIs500(t *testing.T) {
+	m := New(ID("server.does_not_exist"), nil)
+	if m.Status != http.StatusInternalServerError {
+		t.Fatalf("Status = %d, want 500", m.Status)
+	}
+	if m.English != "internal error" {
+		t.Fatalf("English = %q", m.English)
+	}
+	if m.ID != "server.does_not_exist" {
+		t.Fatalf("ID = %q", m.ID)
+	}
+}
+
+func TestAllSortedAndUnique(t *testing.T) {
+	all := All()
+	if len(all) == 0 {
+		t.Fatal("registry is empty")
+	}
+	for i := 1; i < len(all); i++ {
+		if all[i-1].ID >= all[i].ID {
+			t.Fatalf("not strictly sorted at %d: %q then %q", i, all[i-1].ID, all[i].ID)
+		}
+	}
+}
+
+func TestAllReturnsCopy(t *testing.T) {
+	all := All()
+	all[0].English = "mutated"
+	if All()[0].English == "mutated" {
+		t.Fatal("All must return a copy")
+	}
+}
+
+func TestEveryEntryHasDescription(t *testing.T) {
+	for _, e := range All() {
+		if strings.TrimSpace(e.Description) == "" {
+			t.Errorf("%q has no description", e.ID)
+		}
+	}
+}
+
+func TestRemoteClusterEnglishIsSafeICU(t *testing.T) {
+	e, ok := Lookup(ID(httperr.IDRemoteClusterNotImplemented))
+	if !ok {
+		t.Fatal("remote cluster id not registered")
+	}
+	if e.English != httperr.RemoteClusterNotImplemented {
+		t.Fatalf("English = %q", e.English)
+	}
+	if e.Status != http.StatusNotImplemented {
+		t.Fatalf("Status = %d", e.Status)
+	}
+}
+
+func TestExportJSONRoundTrip(t *testing.T) {
+	var buf bytes.Buffer
+	if err := ExportJSON(&buf); err != nil {
+		t.Fatalf("ExportJSON: %v", err)
+	}
+	if !strings.HasSuffix(buf.String(), "]\n") {
+		t.Fatalf("export must end with a newline after the array: %q", buf.String()[len(buf.String())-5:])
+	}
+	var got []Entry
+	if err := json.Unmarshal(buf.Bytes(), &got); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	want := All()
+	if len(got) != len(want) {
+		t.Fatalf("decoded %d entries, want %d", len(got), len(want))
+	}
+	for i := range want {
+		if got[i].ID != want[i].ID || got[i].English != want[i].English || got[i].Description != want[i].Description {
+			t.Fatalf("entry %d = %+v, want %+v", i, got[i], want[i])
+		}
+	}
+}
+
+func TestExportJSONDoesNotEscapeHTML(t *testing.T) {
+	var buf bytes.Buffer
+	if err := ExportJSON(&buf); err != nil {
+		t.Fatalf("ExportJSON: %v", err)
+	}
+	if strings.Contains(buf.String(), `<`) || strings.Contains(buf.String(), `&`) {
+		t.Fatal("export escapes HTML characters")
+	}
+}
diff --git a/api/internal/messages/usage_test.go b/api/internal/messages/usage_test.go
new file mode 100644
index 000000000..c0abec2cd
--- /dev/null
+++ b/api/internal/messages/usage_test.go
@@ -0,0 +1,100 @@
+package messages
+
+import (
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"io/fs"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+// TestEveryMessagesNewLiteralIsRegistered walks the API's internal packages
+// and checks that every messages.New call with a literal id names a
+// registered server.* entry, so a migrated handler cannot ship an id the
+// registry does not know (it would render as "internal error").
+func TestEveryMessagesNewLiteralIsRegistered(t *testing.T) {
+	fset := token.NewFileSet()
+	sites := 0
+	err := filepath.WalkDir(filepath.Join(".."), func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if d.IsDir() {
+			if filepath.Clean(path) == filepath.Join("..", "messages") {
+				return filepath.SkipDir
+			}
+			return nil
+		}
+		if !strings.HasSuffix(path, ".go") || strings.HasSuffix(path, "_test.go") {
+			return nil
+		}
+		file, perr := parser.ParseFile(fset, path, nil, 0)
+		if perr != nil {
+			return perr
+		}
+		ast.Inspect(file, func(n ast.Node) bool {
+			call, ok := n.(*ast.CallExpr)
+			if !ok || len(call.Args) == 0 {
+				return true
+			}
+			sel, ok := call.Fun.(*ast.SelectorExpr)
+			if !ok || sel.Sel.Name != "New" {
+				return true
+			}
+			pkg, ok := sel.X.(*ast.Ident)
+			if !ok || pkg.Name != "messages" {
+				return true
+			}
+			lit := idLiteral(call.Args[0])
+			if lit == "" {
+				return true
+			}
+			sites++
+			pos := fset.Position(call.Pos())
+			if !strings.HasPrefix(lit, "server.") {
+				t.Errorf("%s: messages.New(%q) must use a server.* id", pos, lit)
+			}
+			if _, ok := Lookup(ID(lit)); !ok {
+				t.Errorf("%s: messages.New(%q) is not registered", pos, lit)
+			}
+			return true
+		})
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("walk: %v", err)
+	}
+	if sites < 100 {
+		t.Fatalf("found %d messages.New call sites, want at least 100 (walker broken?)", sites)
+	}
+}
+
+// idLiteral returns the string value of a literal id argument, accepting
+// a bare string literal or a conversion ID("...") / messages.ID("...").
+// Non-literal arguments return "".
+func idLiteral(e ast.Expr) string {
+	if conv, ok := e.(*ast.CallExpr); ok && len(conv.Args) == 1 {
+		switch fn := conv.Fun.(type) {
+		case *ast.Ident:
+			if fn.Name == "ID" {
+				e = conv.Args[0]
+			}
+		case *ast.SelectorExpr:
+			if id, ok := fn.X.(*ast.Ident); ok && id.Name == "messages" && fn.Sel.Name == "ID" {
+				e = conv.Args[0]
+			}
+		}
+	}
+	lit, ok := e.(*ast.BasicLit)
+	if !ok || lit.Kind != token.STRING {
+		return ""
+	}
+	s, err := strconv.Unquote(lit.Value)
+	if err != nil {
+		return ""
+	}
+	return s
+}
diff --git a/api/internal/notify/format.go b/api/internal/notify/format.go
index c6efef9b9..b651e4c5f 100644
--- a/api/internal/notify/format.go
+++ b/api/internal/notify/format.go
@@ -32,32 +32,68 @@ func title(e Event) string {
 	if inst == "" {
 		inst = "Gameplane"
 	}
-	what := strings.ReplaceAll(string(e.Type), ".", " ")
+	what := eventName(e)
+	if e.Name == "" {
+		return render(e.lang, "notify.title.unnamed", map[string]any{"instance": inst, "event": what})
+	}
+	return render(e.lang, "notify.title.named", map[string]any{
+		"instance":  inst,
+		"event":     what,
+		"namespace": e.Namespace,
+		"name":      e.Name,
+	})
+}
+
+// eventName returns the translated event name used inside the headline. An
+// event type without a notify.event.* entry keeps the raw dotted name spelled
+// with spaces, as before the catalog existed.
+func eventName(e Event) string {
 	if e.Test {
-		what = "test notification"
+		return render(e.lang, "notify.event.test", nil)
 	}
-	if e.Name == "" {
-		return fmt.Sprintf("[%s] %s", inst, what)
+	id := "notify.event." + string(e.Type)
+	if !hasMessage(id) {
+		return strings.ReplaceAll(string(e.Type), ".", " ")
+	}
+	return render(e.lang, id, nil)
+}
+
+// hasMessage reports whether id is one of the notify.* catalog entries.
+func hasMessage(id string) bool {
+	for _, m := range Messages() {
+		if string(m.ID) == id {
+			return true
+		}
 	}
-	return fmt.Sprintf("[%s] %s: %s/%s", inst, what, e.Namespace, e.Name)
+	return false
 }
 
 // detail composes the reason/message pair into one line; test events get
-// fixed copy so a test send never renders an empty body.
+// fixed copy so a test send never renders an empty body. Kubernetes reason
+// and message text is quoted verbatim.
 func detail(e Event) string {
 	switch {
 	case e.Reason != "" && e.Message != "":
-		return e.Reason + " — " + e.Message
+		return render(e.lang, "notify.detail.reason_message", map[string]any{"reason": e.Reason, "message": e.Message})
 	case e.Message != "":
 		return e.Message
 	case e.Reason != "":
 		return e.Reason
 	case e.Test:
-		return "This is a test notification from Gameplane. Your sink is wired up correctly."
+		return render(e.lang, "notify.detail.test", nil)
 	}
 	return ""
 }
 
+// text is the one-line sentence Slack shows, without the emoji: the headline,
+// then the detail after an em dash when there is one.
+func text(e Event) string {
+	if d := detail(e); d != "" {
+		return title(e) + " — " + d
+	}
+	return title(e)
+}
+
 // formatDiscord renders e as a Discord webhook execute payload: one embed,
 // color-coded by outcome.
 func formatDiscord(e Event) ([]byte, error) {
@@ -106,7 +142,27 @@ func formatSlack(e Event) ([]byte, error) {
 // formatWebhook ships the full structured event so generic consumers can
 // route on any field.
 func formatWebhook(e Event) ([]byte, error) {
-	return json.Marshal(e)
+	lang := e.lang
+	if lang == "" {
+		lang = "en"
+	}
+	// Embedding Event flattens its fields, so every existing key keeps its
+	// name, order and value; the three additive fields come last.
+	return json.Marshal(webhookPayload{
+		Event:    e,
+		Language: lang,
+		Title:    title(e),
+		Text:     text(e),
+	})
+}
+
+// webhookPayload is the generic webhook body: the Event fields plus the
+// language the text was rendered in and the rendered headline and sentence.
+type webhookPayload struct {
+	Event
+	Language string `json:"language"`
+	Title    string `json:"title"`
+	Text     string `json:"text"`
 }
 
 // formatNtfy renders e for an ntfy topic POST: the detail is the
@@ -153,7 +209,7 @@ func formatEmail(e Event) (subject, body string) {
 		fmt.Fprintf(&b, "Instance:  %s\r\n", e.Instance)
 	}
 	if e.Test {
-		b.WriteString("\r\nThis is a test notification from Gameplane. Your sink is wired up correctly.\r\n")
+		b.WriteString("\r\n" + render(e.lang, "notify.detail.test", nil) + "\r\n")
 	}
 	return subject, b.String()
 }
diff --git a/api/internal/notify/language.go b/api/internal/notify/language.go
new file mode 100644
index 000000000..af0aa70c8
--- /dev/null
+++ b/api/internal/notify/language.go
@@ -0,0 +1,71 @@
+package notify
+
+import (
+	"context"
+	"encoding/json"
+	"strings"
+
+	"golang.org/x/text/language"
+
+	"github.com/GameplanePanel/gameplane/i18n/catalog"
+	"github.com/GameplanePanel/gameplane/i18n/icu"
+)
+
+var (
+	isListed      = catalog.IsListed // swapped in tests
+	lookupMessage = catalog.Lookup   // swapped in tests
+)
+
+// resolveLanguage picks the first of sinkLang, instanceDefault, "en" that the
+// catalog lists. An empty candidate is skipped. "en" is always listed.
+func resolveLanguage(sinkLang, instanceDefault string) string {
+	for _, c := range []string{sinkLang, instanceDefault} {
+		if c != "" && isListed(c) {
+			return c
+		}
+	}
+	return "en"
+}
+
+// render formats notify message id for lang (BCP 47; "" means "en"). It asks the
+// catalog first and falls back to the English text from Messages() rendered with
+// icu.Parse/icu.Format(language.English), so output never goes empty.
+func render(lang, id string, args map[string]any) string {
+	if lang == "" {
+		lang = "en"
+	}
+	tag, err := language.Parse(lang)
+	if err != nil {
+		tag = language.English
+	}
+	if s, ok := lookupMessage(tag, id, args); ok {
+		return s
+	}
+	for _, m := range Messages() {
+		if string(m.ID) != id {
+			continue
+		}
+		msg, err := icu.Parse(m.English)
+		if err != nil {
+			return m.English
+		}
+		return icu.Format(msg, language.English, args)
+	}
+	return id
+}
+
+// defaultLanguage reads the admin config section "i18n" ({"defaultLanguage": tag});
+// "" on any miss or error.
+func (n *Notifier) defaultLanguage(ctx context.Context) string {
+	raw, ok, err := n.store.ConfigValue(ctx, "i18n")
+	if err != nil || !ok {
+		return ""
+	}
+	var c struct {
+		DefaultLanguage string `json:"defaultLanguage"`
+	}
+	if json.Unmarshal([]byte(raw), &c) != nil {
+		return ""
+	}
+	return strings.TrimSpace(c.DefaultLanguage)
+}
diff --git a/api/internal/notify/language_test.go b/api/internal/notify/language_test.go
new file mode 100644
index 000000000..da0d9eff5
--- /dev/null
+++ b/api/internal/notify/language_test.go
@@ -0,0 +1,253 @@
+package notify
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync"
+	"testing"
+
+	"golang.org/x/text/language"
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	kubefake "k8s.io/client-go/kubernetes/fake"
+
+	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
+	"github.com/GameplanePanel/gameplane/i18n/catalog"
+	"github.com/GameplanePanel/gameplane/i18n/icu"
+)
+
+// listedOnly points isListed at a fixed set of tags for one test.
+func listedOnly(t *testing.T, tags ...string) {
+	t.Helper()
+	prev := isListed
+	isListed = func(tag string) bool {
+		for _, want := range tags {
+			if tag == want {
+				return true
+			}
+		}
+		return false
+	}
+	t.Cleanup(func() { isListed = prev })
+}
+
+func TestLoadSinks_Language(t *testing.T) {
+	store := newTestStore(t)
+	n := &Notifier{store: store}
+	putConfig(t, store, "notifications",
+		`{"sinks":[{"name":"a","kind":"webhook","enabled":true,"configRef":"hook","language":"fr"},{"name":"b","kind":"webhook","enabled":true}]}`)
+	sinks, err := n.loadSinks(context.Background())
+	if err != nil {
+		t.Fatalf("loadSinks: %v", err)
+	}
+	if len(sinks) != 2 || sinks[0].Language != "fr" || sinks[1].Language != "" {
+		t.Fatalf("sinks = %+v; want language fr then empty", sinks)
+	}
+}
+
+func TestEnglishOutputUnchanged(t *testing.T) {
+	events := []Event{
+		{Type: EventBackupFailed, TS: "t", Kind: "Backup", Name: "nightly", Namespace: "gameplane-games", Reason: "BackupFailed", Message: "restic exited with code 1", Instance: "prod"},
+		{Type: EventServerUnhealthy, TS: "t", Kind: "GameServer", Name: "mc", Namespace: "gameplane-games", Instance: "prod"},
+		{Type: EventBackupSucceeded, TS: "t", Instance: "prod"},
+		{Type: EventTest, TS: "t", Instance: "prod", Test: true},
+	}
+	for _, base := range events {
+		en := base
+		en.lang = "en"
+		if title(base) != title(en) || detail(base) != detail(en) || text(base) != text(en) {
+			t.Fatalf("%s: empty and en renderings differ", base.Type)
+		}
+		a, _ := formatSlack(base)
+		b, _ := formatSlack(en)
+		if string(a) != string(b) {
+			t.Fatalf("%s: slack differs: %s vs %s", base.Type, a, b)
+		}
+		subjA, bodyA := formatEmail(base)
+		subjB, bodyB := formatEmail(en)
+		if subjA != subjB || bodyA != bodyB {
+			t.Fatalf("%s: email differs", base.Type)
+		}
+	}
+
+	failed := events[0]
+	if got := title(failed); got != "[prod] backup failed: gameplane-games/nightly" {
+		t.Errorf("title = %q", got)
+	}
+	if got := detail(failed); got != "BackupFailed — restic exited with code 1" {
+		t.Errorf("detail = %q", got)
+	}
+	test := events[3]
+	if got := title(test); got != "[prod] test notification" {
+		t.Errorf("test title = %q", got)
+	}
+	if got := detail(test); got != "This is a test notification from Gameplane. Your sink is wired up correctly." {
+		t.Errorf("test detail = %q", got)
+	}
+	if got := title(Event{Type: EventBackupFailed, Instance: "prod", Test: false}); got != "[prod] backup failed" {
+		t.Errorf("unnamed title = %q", got)
+	}
+}
+
+func TestRenderUsesSinkLanguage(t *testing.T) {
+	prev := lookupMessage
+	lookupMessage = func(tag language.Tag, id string, args map[string]any) (string, bool) {
+		if base, _ := tag.Base(); base.String() == "fr" {
+			return "FR:" + id, true
+		}
+		return catalog.Lookup(tag, id, args)
+	}
+	t.Cleanup(func() { lookupMessage = prev })
+
+	fr := Event{Type: EventBackupFailed, Name: "nightly", Namespace: "ns", Instance: "prod", lang: "fr"}
+	if got := title(fr); got != "FR:notify.title.named" {
+		t.Errorf("fr title = %q", got)
+	}
+
+	en := Event{Type: EventBackupFailed, Name: "nightly", Namespace: "ns", Instance: "prod", lang: "en", Reason: "R<x>", Message: "M {y} 'z'"}
+	if got := title(en); got != "[prod] backup failed: ns/nightly" {
+		t.Errorf("en title = %q", got)
+	}
+	if got := detail(en); got != "R<x> — M {y} 'z'" {
+		t.Errorf("en detail = %q; Kubernetes text must pass through verbatim", got)
+	}
+}
+
+func TestResolveLanguage(t *testing.T) {
+	listedOnly(t, "en", "fr")
+	cases := []struct{ sink, def, want string }{
+		{"fr", "de", "fr"},
+		{"zz", "fr", "fr"},
+		{"", "", "en"},
+		{"zz", "zz", "en"},
+		{"", "fr", "fr"},
+	}
+	for _, c := range cases {
+		if got := resolveLanguage(c.sink, c.def); got != c.want {
+			t.Errorf("resolveLanguage(%q, %q) = %q; want %q", c.sink, c.def, got, c.want)
+		}
+	}
+}
+
+func TestFormatWebhookAddsLanguageTitleText(t *testing.T) {
+	e := Event{Type: EventBackupFailed, TS: "t", Name: "nightly", Namespace: "ns", Reason: "R", Message: "M", Instance: "prod", lang: "fr"}
+	raw, err := formatWebhook(e)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var got map[string]any
+	if err := json.Unmarshal(raw, &got); err != nil {
+		t.Fatal(err)
+	}
+	want := map[string]any{
+		"type": "backup.failed", "ts": "t", "name": "nightly", "namespace": "ns",
+		"reason": "R", "message": "M", "instance": "prod",
+		"language": "fr", "title": title(e), "text": text(e),
+	}
+	for k, v := range want {
+		if got[k] != v {
+			t.Errorf("%s = %v; want %v", k, got[k], v)
+		}
+	}
+
+	raw, _ = formatWebhook(Event{Type: EventTest, TS: "t", Test: true})
+	got = map[string]any{}
+	if err := json.Unmarshal(raw, &got); err != nil {
+		t.Fatal(err)
+	}
+	if got["language"] != "en" {
+		t.Errorf("empty lang: language = %v; want en", got["language"])
+	}
+}
+
+func TestMessagesHaveDescriptionsAndParse(t *testing.T) {
+	seen := map[messages.ID]bool{}
+	for _, m := range Messages() {
+		if m.Description == "" {
+			t.Errorf("%s: empty description", m.ID)
+		}
+		if !strings.HasPrefix(string(m.ID), "notify.") {
+			t.Errorf("%s: id lacks notify. prefix", m.ID)
+		}
+		if seen[m.ID] {
+			t.Errorf("%s: duplicate id", m.ID)
+		}
+		seen[m.ID] = true
+		if _, err := icu.Parse(m.English); err != nil {
+			t.Errorf("%s: parse: %v", m.ID, err)
+		}
+	}
+}
+
+func TestFanOutRendersInSinkOrDefaultLanguage(t *testing.T) {
+	listedOnly(t, "en", "fr")
+	store := newTestStore(t)
+
+	var mu sync.Mutex
+	bodies := map[string]map[string]any{}
+	record := func(name string) *httptest.Server {
+		return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			data, _ := io.ReadAll(r.Body)
+			var doc map[string]any
+			_ = json.Unmarshal(data, &doc)
+			mu.Lock()
+			bodies[name] = doc
+			mu.Unlock()
+			w.WriteHeader(http.StatusNoContent)
+		}))
+	}
+	srvA := record("a")
+	defer srvA.Close()
+	srvB := record("b")
+	defer srvB.Close()
+
+	secret := func(name, url string) *corev1.Secret {
+		return &corev1.Secret{
+			ObjectMeta: metav1.ObjectMeta{
+				Name: name, Namespace: "gameplane-system",
+				Labels: map[string]string{SinkSecretLabel: "true"},
+			},
+			Data: map[string][]byte{"url": []byte(url)},
+		}
+	}
+	n := &Notifier{
+		store:     store,
+		k:         &kube.Client{Typed: kubefake.NewClientset(secret("hook-a", srvA.URL), secret("hook-b", srvB.URL))},
+		controlNS: "gameplane-system",
+		client:    testNotifier().client,
+		ch:        make(chan Event, 1),
+	}
+	fastRetries(t)
+
+	putConfig(t, store, "i18n", `{"defaultLanguage":"fr"}`)
+	putConfig(t, store, "notifications",
+		`{"sinks":[`+
+			`{"name":"a","kind":"webhook","enabled":true,"configRef":"hook-a","events":["backup.failed"],"language":"fr"},`+
+			`{"name":"b","kind":"webhook","enabled":true,"configRef":"hook-b","events":["backup.failed"]}]}`)
+	n.fanOut(context.Background(), Event{Type: EventBackupFailed, TS: "t", Name: "nightly", Namespace: "ns"})
+	mu.Lock()
+	if bodies["a"]["language"] != "fr" {
+		t.Errorf("sink a language = %v; want fr", bodies["a"]["language"])
+	}
+	if bodies["b"]["language"] != "fr" {
+		t.Errorf("sink b (instance default) language = %v; want fr", bodies["b"]["language"])
+	}
+	mu.Unlock()
+
+	putConfig(t, store, "i18n", `{}`)
+	bodies = map[string]map[string]any{}
+	n.fanOut(context.Background(), Event{Type: EventBackupFailed, TS: "t", Name: "nightly", Namespace: "ns"})
+	mu.Lock()
+	defer mu.Unlock()
+	if bodies["b"]["language"] != "en" {
+		t.Errorf("sink b with no default language = %v; want en", bodies["b"]["language"])
+	}
+	if bodies["a"]["language"] != "fr" {
+		t.Errorf("sink a language = %v; want fr", bodies["a"]["language"])
+	}
+}
diff --git a/api/internal/notify/messages.go b/api/internal/notify/messages.go
new file mode 100644
index 000000000..4c08da6f6
--- /dev/null
+++ b/api/internal/notify/messages.go
@@ -0,0 +1,66 @@
+package notify
+
+import "github.com/GameplanePanel/gameplane/api/internal/messages"
+
+// Messages returns the notify.* catalog entries. They are the single source for
+// i18n/locales/en/app.json (written by `make i18n-sync`) and the English
+// fallback when the catalog cannot answer.
+func Messages() []messages.Entry {
+	return []messages.Entry{
+		{
+			ID:          "notify.title.named",
+			English:     "[{instance}] {event}: {namespace}/{name}",
+			Description: "Headline of a notification about a named resource. instance is the Gameplane instance name, event is the event name (for example \"backup failed\"), namespace and name identify the resource.",
+		},
+		{
+			ID:          "notify.title.unnamed",
+			English:     "[{instance}] {event}",
+			Description: "Headline of a notification without a resource, such as a test send. instance is the Gameplane instance name, event is the event name.",
+		},
+		{
+			ID:          "notify.event.server.unhealthy",
+			English:     "server unhealthy",
+			Description: "Event name used inside a notification headline when a game server becomes unhealthy.",
+		},
+		{
+			ID:          "notify.event.server.recovered",
+			English:     "server recovered",
+			Description: "Event name used inside a notification headline when a game server recovers.",
+		},
+		{
+			ID:          "notify.event.backup.failed",
+			English:     "backup failed",
+			Description: "Event name used inside a notification headline when a backup fails.",
+		},
+		{
+			ID:          "notify.event.backup.succeeded",
+			English:     "backup succeeded",
+			Description: "Event name used inside a notification headline when a backup succeeds.",
+		},
+		{
+			ID:          "notify.event.restore.failed",
+			English:     "restore failed",
+			Description: "Event name used inside a notification headline when a restore fails.",
+		},
+		{
+			ID:          "notify.event.restore.succeeded",
+			English:     "restore succeeded",
+			Description: "Event name used inside a notification headline when a restore succeeds.",
+		},
+		{
+			ID:          "notify.event.test",
+			English:     "test notification",
+			Description: "Event name used inside the headline of a test notification.",
+		},
+		{
+			ID:          "notify.detail.reason_message",
+			English:     "{reason} — {message}",
+			Description: "Body line that joins the Kubernetes reason and message of an event. The reason and message are quoted from Kubernetes in English and stay untranslated. The dash is an em dash.",
+		},
+		{
+			ID:          "notify.detail.test",
+			English:     "This is a test notification from Gameplane. Your sink is wired up correctly.",
+			Description: "Body of a test notification sent from Admin Settings.",
+		},
+	}
+}
diff --git a/api/internal/notify/notify.go b/api/internal/notify/notify.go
index 8dc69a4b5..9f8de6fa0 100644
--- a/api/internal/notify/notify.go
+++ b/api/internal/notify/notify.go
@@ -45,7 +45,9 @@ const queueSize = 256
 
 // Event is one notifiable occurrence. It is also the exact JSON payload
 // shipped to generic webhook sinks, so field renames are a breaking change
-// for webhook consumers.
+// for webhook consumers. Webhook payloads add three fields after these
+// (language, title, text); they are additive and every field above keeps its
+// name and value.
 type Event struct {
 	Type      EventType `json:"type"`
 	TS        string    `json:"ts"`
@@ -56,6 +58,7 @@ type Event struct {
 	Message   string    `json:"message,omitempty"`
 	Instance  string    `json:"instance,omitempty"`
 	Test      bool      `json:"test,omitempty"`
+	lang      string    // BCP 47 rendering language; "" renders English. Never serialized.
 }
 
 // Notifier watches CRD status transitions and delivers matching events to
@@ -124,6 +127,7 @@ func (n *Notifier) fanOut(ctx context.Context, e Event) {
 	if err == nil {
 		e.Instance = n.instanceName(loadCtx)
 	}
+	def := n.defaultLanguage(loadCtx)
 	cancel()
 	if err != nil {
 		slog.Warn("notification fan-out: loading sinks failed", "err", err)
@@ -146,7 +150,9 @@ func (n *Notifier) fanOut(ctx context.Context, e Event) {
 			slog.Warn("notification sink secret unavailable", "sink", s.Name, "err", err)
 			continue
 		}
-		n.deliverWithRetry(ctx, s, secret, e)
+		ev := e
+		ev.lang = resolveLanguage(s.Language, def)
+		n.deliverWithRetry(ctx, s, secret, ev)
 	}
 }
 
@@ -176,6 +182,7 @@ func (n *Notifier) DeliverTest(ctx context.Context, sinkName string) error {
 			Instance: n.instanceName(ctx),
 			Test:     true,
 		}
+		e.lang = resolveLanguage(s.Language, n.defaultLanguage(ctx))
 		if err := n.deliver(ctx, s, secret, e); err != nil {
 			deliveries.WithLabelValues(s.Kind, "failed").Inc()
 			return fmt.Errorf("deliver test to %q: %w", sinkName, err)
diff --git a/api/internal/notify/sinks.go b/api/internal/notify/sinks.go
index b4a88b157..4944f54a3 100644
--- a/api/internal/notify/sinks.go
+++ b/api/internal/notify/sinks.go
@@ -23,6 +23,7 @@ type Sink struct {
 	Enabled   bool     `json:"enabled"`
 	ConfigRef string   `json:"configRef"`
 	Events    []string `json:"events"`
+	Language  string   `json:"language,omitempty"` // BCP 47 tag of a listed language; empty = instance default
 }
 
 // loadSinks reads the persisted notifications config. A missing row means
diff --git a/api/internal/rbac/rbac.go b/api/internal/rbac/rbac.go
index ff0cbc645..01bbdede0 100644
--- a/api/internal/rbac/rbac.go
+++ b/api/internal/rbac/rbac.go
@@ -27,6 +27,8 @@ import (
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 
 	"github.com/GameplanePanel/gameplane/api/internal/auth"
+	"github.com/GameplanePanel/gameplane/api/internal/httperr"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/scope"
 )
 
@@ -78,12 +80,12 @@ func Middleware(fetch ServerFetcher) func(http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
 			u := auth.UserFromContext(req.Context())
 			if u == nil {
-				http.Error(w, "unauthenticated", http.StatusUnauthorized)
+				httperr.WriteMessage(w, req, messages.New("server.common.unauthenticated", nil))
 				return
 			}
 			r, ok := match(req.Method, req.URL.Path)
 			if !ok {
-				http.Error(w, "forbidden", http.StatusForbidden)
+				httperr.WriteMessage(w, req, messages.New("server.forbidden", nil))
 				return
 			}
 			if r.perm == "" { // any authenticated user
@@ -100,7 +102,7 @@ func Middleware(fetch ServerFetcher) func(http.Handler) http.Handler {
 			if Namespaced(r.perm) {
 				resolved, err := scope.Resolve(req)
 				if err != nil {
-					http.Error(w, "namespace not permitted", http.StatusBadRequest)
+					httperr.WriteMessage(w, req, messages.New("server.common.namespace_not_permitted", nil))
 					return
 				}
 				ns = resolved
@@ -110,7 +112,7 @@ func Middleware(fetch ServerFetcher) func(http.Handler) http.Handler {
 				if fetch != nil {
 					resolvedCluster, err := scope.ResolveCluster(req, fetch)
 					if err != nil {
-						http.Error(w, "cluster not permitted", http.StatusBadRequest)
+						httperr.WriteMessage(w, req, messages.New("server.cluster_forbidden", nil))
 						return
 					}
 					cl = resolvedCluster
@@ -128,7 +130,7 @@ func Middleware(fetch ServerFetcher) func(http.Handler) http.Handler {
 						// (owner-only deletion) are permitted on the exact server path.
 						// Sub-resource writes (files, players, mods) continue through ownership fallback.
 						if isExact && req.Method != http.MethodGet && req.Method != http.MethodHead && req.Method != http.MethodDelete {
-							http.Error(w, "forbidden", http.StatusForbidden)
+							httperr.WriteMessage(w, req, messages.New("server.forbidden", nil))
 							return
 						}
 						obj, err := fetch.GetServer(req.Context(), cl, ns, name)
@@ -146,7 +148,7 @@ func Middleware(fetch ServerFetcher) func(http.Handler) http.Handler {
 						}
 					}
 				}
-				http.Error(w, "forbidden", http.StatusForbidden)
+				httperr.WriteMessage(w, req, messages.New("server.forbidden", nil))
 				return
 			}
 			// Owner-only server operations need the server's owner or an
@@ -155,12 +157,12 @@ func Middleware(fetch ServerFetcher) func(http.Handler) http.Handler {
 			if Namespaced(r.perm) && !u.Can("*", true, cl, ns) {
 				if name, verb, isExact, ok := parseServerPath(req.URL.Path); ok && ownerOnlyOperation(req.Method, verb, isExact) {
 					if fetch == nil {
-						http.Error(w, "forbidden", http.StatusForbidden)
+						httperr.WriteMessage(w, req, messages.New("server.forbidden", nil))
 						return
 					}
 					obj, err := fetch.GetServer(req.Context(), cl, ns, name)
 					if err != nil || obj == nil || ownershipRole(obj, u.ID) != roleOwner {
-						http.Error(w, "forbidden", http.StatusForbidden)
+						httperr.WriteMessage(w, req, messages.New("server.forbidden", nil))
 						return
 					}
 					// This grant still depends on owning this exact object, even
diff --git a/api/internal/ws/attach.go b/api/internal/ws/attach.go
index 86705c55e..39e34bb85 100644
--- a/api/internal/ws/attach.go
+++ b/api/internal/ws/attach.go
@@ -18,6 +18,7 @@ import (
 
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/scope"
 )
 
@@ -76,7 +77,7 @@ func (a *attachProxy) handle(w http.ResponseWriter, req *http.Request) {
 	// servers so the -0 suffix is the only pod that ever exists for a
 	// given GameServer.
 	if len(validation.IsDNS1123Subdomain(name)) != 0 {
-		http.Error(w, "invalid server name", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.ws.invalid_server_name", nil))
 		return
 	}
 	pod, err := serverPod(req.Context(), a.k, ns, name)
diff --git a/api/internal/ws/podlogs.go b/api/internal/ws/podlogs.go
index 0554087dc..557edaab6 100644
--- a/api/internal/ws/podlogs.go
+++ b/api/internal/ws/podlogs.go
@@ -18,6 +18,7 @@ import (
 
 	"github.com/GameplanePanel/gameplane/api/internal/httperr"
 	"github.com/GameplanePanel/gameplane/api/internal/kube"
+	"github.com/GameplanePanel/gameplane/api/internal/messages"
 	"github.com/GameplanePanel/gameplane/api/internal/scope"
 )
 
@@ -69,7 +70,7 @@ func (h *podLogProxy) handle(w http.ResponseWriter, req *http.Request) {
 	// StatefulSet replica naming — the operator pins replicas=1, so -0 is
 	// the only pod that ever exists for a given GameServer.
 	if len(validation.IsDNS1123Subdomain(name)) != 0 {
-		http.Error(w, "invalid server name", http.StatusBadRequest)
+		httperr.WriteMessage(w, req, messages.New("server.ws.invalid_server_name", nil))
 		return
 	}
 	podName := name + "-0"
diff --git a/api/specs.md b/api/specs.md
index b3ce7ca86..d508a5c43 100644
--- a/api/specs.md
+++ b/api/specs.md
@@ -48,6 +48,7 @@ api/
 │   ├── steam/            # Steam Workshop ID resolver: cache + singleflight-deduped upstream lookups
 │   ├── scope/            # namespace + cluster resolution from request context
 │   ├── telemetry/        # optional anonymous usage metrics collection
+│   ├── messages/         # localizable error registry (ids, English ICU, status)
 │   ├── httperr/          # error -> HTTP status classification (safe message for client, full error logged)
 │   └── [test files]
 └── go.mod, go.sum
@@ -61,7 +62,7 @@ api/
 - **db:** driver-selectable (modernc.org/sqlite or pgx/v5 via postgres build tag), migrations (001-012 per dialect in `migrations/sqlite/` and `migrations/postgres/`; 013+ shared and portable in `migrations/common/`), Store (query interface); queries use `?` placeholders, rebound to `$n` by the Postgres connection (`db.Rebind`); migration 015 (`migrations/common/015_telemetry_state.sql`) adds `telemetry_state` (singleton row: consent source, install ID, notice shown time, report schedule `next_due_at`/`last_attempt_at`/`last_success_at`, `last_outcome`, `consecutive_failures`, extended-fallback fields `ext_unsupported_until`/`ext_unsupported_endpoint`, `signing_secret`, `last_id_rotation_at`; seeded in Go by `Store.Migrate` from the existing `telemetry` config value) and `telemetry_notice_acks` (one row per admin who dismissed the notice: `user_id`, `acked_at`, `action`; rows are removed in Go when the user is deleted)
 - **kube:** Client (K8s API wrapper), Registry (per-cluster clients from Cluster CRDs), watch (cluster-config sync)
 - **audit:** Auditor (insert to DB + distribute to sinks), webhook sink (POST JSON to URL), S3 sink (object storage), hash-chain (detect tampering)
-- **notify:** Notifier (watch GameServer/Backup/Restore status, format + deliver to sinks), sinks (Discord, Slack, SMTP, webhook)
+- **notify:** Notifier (watch GameServer/Backup/Restore status, format + deliver to sinks), sinks (Discord, Slack, SMTP, webhook, ntfy); per-sink `language` (BCP 47, optional), rendered from the `notify.*` entries of the language packs; webhook payloads add `language`, `title`, `text`
 - **ws:** Mount (WebSocket router), agent-client (JSON agent reads), transport (shared HTTP/WebSocket agent connection), actions (RCON/PTY execution), attach (SPDY proxy), podlogs (live pod logs)
 - **registry:** provider types (each implements Search, Details, Manifest, Download), Set (versioned provider pool with key fallback)
 - **scope:** ResolveNamespace (extract from path or default), ResolveCluster (validate `?cluster=` against registry)
@@ -95,6 +96,7 @@ The HTTP server listens on `:8000` (configurable) with these route groups. Prome
 
 **Public (pre-auth):**
 - `/auth/providers` — GET: list enabled login methods (no version/host/count, login privacy)
+- `/auth/locale` — GET: the instance default language tag for the login page, `{"defaultLanguage": "<tag>"}` and nothing else (spec 019; see [Language and localizable errors](#language-and-localizable-errors-spec-019))
 - `/auth/login` — POST: argon2id auth + session creation (rate-limited per IP + user)
 - `/auth/logout` — POST: session deletion
 - `/auth/oidc/{provider}/start` — GET: IdP authorization flow start
@@ -147,6 +149,7 @@ The HTTP server listens on `:8000` (configurable) with these route groups. Prome
 - `/modules/sources/{name}` — GET, PUT, DELETE: manage ModuleSource CRDs (cluster-scoped)
 - `/modules/sources/{name}/upload`, `/modules/sources/{name}/upload/{module}` — bundle upload/delete
 - `/modules/catalog` — GET: merged catalog across sources, with installation state
+- `/modules/{name}/locales/{tag}` — GET: the module's translated messages for a language as a flat id → message map, read from the operator-written `<name>-locales` ConfigMap. The tag falls back to its base language; an unknown or malformed tag, or a module without translations, returns `200 {}`; values are the validated ICU message strings, uncompiled. 404 only when the Module does not exist. Requires `modules:read`.
 - `/modules/builder/{archetypes,scaffold,validate,preview,export}` — module builder workflow
 - `/registry/{provider}/search`, `/{id}` — live mod registry queries (CurseForge, Modrinth, Spigot, etc.)
 - `/mod-updates/{name}` — GET: available updates for a mod
@@ -160,6 +163,7 @@ The HTTP server listens on `:8000` (configurable) with these route groups. Prome
 - `/users/me/servers` — GET: own GameServers (owner/collaborator)
 - `/users/me/preferences` — GET/PUT: own theme/styling preferences (feature 016)
 - `/users/me/preferences/reset` — POST: reset own theme preferences to defaults (feature 016)
+- `/users/me/language` — PUT: set or clear own language choice (spec 019; see below)
 - `/users` — GET, POST: list and create users
 - `/users/{id}` — PATCH, DELETE: manage users (admin only). DELETE runs `db.Store.DeleteUser`: one transaction deletes the user's `oidc_links`, `user_preferences`, `sessions`, `api_tokens` and role bindings, revokes the share links the user created (sets `revoked_at`), then deletes the `users` row. It does not rely on FK cascades (off on SQLite). An SSO subject whose user was deleted is provisioned as a new user on its next login
 - **User list, lookup and create (`POST /users`) responses** include a `createdAt` field: `db.NormalizeTimestamp` passes RFC3339 values through unchanged, converts the legacy "YYYY-MM-DD HH:MM:SS" format from older migrations to RFC3339 UTC, and passes through unrecognized stored values unchanged.
@@ -175,7 +179,7 @@ The HTTP server listens on `:8000` (configurable) with these route groups. Prome
 - `/admin/telemetry/install-id` — POST (`config:manage`): replace the install ID, keep the signing secret and schedule; returns `{"installId"}`; 409 when extended is off or the operator disabled telemetry
 - `/admin/telemetry/notice` — GET (`config:read`; returns `{"pending":false}` unless the caller also holds `config:manage`): whether the first-login notice is pending for the caller, with destination host and the exact basic/extended field lists; POST (`config:manage`) `{"action": "seen"|"keep"|"extended-off"|"all-off"}` records the caller's dismissal (`seen` only sets the notice-shown time and opens the report schedule, recording no ack), 204 on success, 409 when not pending (except `seen`) or the operator disabled telemetry. RBAC entries sit before the `/admin/*` fallback in `rbac.go`
 - The telemetry consent itself is saved through `PUT /admin/config/telemetry` (`{"sendMetrics": bool, "extended": bool}`; `sendMetrics:false` forces `extended:false`; 409 when the operator disabled telemetry). The save runs in one transaction with the consent source, install ID and schedule updates
-- `/admin/notifications` — PATCH config + test-send to sinks
+- `/admin/notifications` — PATCH config + test-send to sinks; per-sink `language` (BCP 47, optional), rendered from the `notify.*` entries of the language packs; webhook payloads add `language`, `title`, `text`
 - `/admin/auth` — PATCH identity-provider secrets
 - `/admin/registries/{provider}/secret` — PATCH mod-registry API keys
 - `/admin/system-logs` — GET: control-plane pod logs
@@ -282,7 +286,7 @@ trust assumptions, rotation behavior and surfaces outside this protocol.
 
 - **DELETE `/servers/{name}:capture`** — Remove a completed or failed capture. Remote deletion confirms sidecar file cleanup before deleting the NetworkCapture with its UID precondition; gateway failure retains the resource for retry. A stale or replaced capture cannot delete another capture's bytes.
 
-- **Error responses:** All errors are plain text via `httperr.WriteCode()`, no JSON envelope. Status codes include 400 (validation), 404 (not found or stale identity), 409 (conflict/wrong state), 501 (capture feature or required gateway capability unavailable), 502/504 (gateway transport failure), 503 (sidecar unavailable), and 500 (internal error).
+- **Error responses:** All errors are plain text via `httperr.WriteCode()`, no JSON envelope; callers that send `Accept: application/problem+json` get RFC 9457 documents (see Problem document negotiation). Status codes include 400 (validation), 404 (not found or stale identity), 409 (conflict/wrong state), 501 (capture feature or required gateway capability unavailable), 502/504 (gateway transport failure), 503 (sidecar unavailable), and 500 (internal error).
 
 **Fully implemented endpoints (all routing registered, RBAC gated, handlers complete):**
 
@@ -666,6 +670,24 @@ Foreign keys are enforced only on Postgres (modernc-sqlite runs with FK OFF); th
 ### Upload limits
 - **Module bundle upload** (`POST /modules/sources/{name}/upload`): the compressed body is capped at 900 KiB (413 above it). Extraction caps each member at 900 KiB, the archive at 256 distinct paths, the running total of extracted bytes at 4 MiB (`maxUploadExtractedBytes`, repeated member names included), and the whole decompressed tar stream (including headers and entries extraction skips) at 5 MiB (`maxUploadDecompressedBytes`, covering tar framing). Extraction stops at the first member that crosses a limit, and the request gets 400. The four kept bundle files must together stay under 900 KiB.
 
+### Language and localizable errors (spec 019)
+
+**Storage (migration `016_user_language.sql`):** `user_preferences.language` is a nullable BCP 47 tag. `NULL` means the user has no saved choice and follows the instance default. Preference writes never touch the column: `UpsertPreferences` and `ResetPreferences` leave it alone, and `db.Store.SetLanguage` owns it. `SetLanguage` inserts a default row when the user has none.
+
+**Endpoints:**
+- **PUT `/users/me/language`** — body `{"language": "<tag>" | null}`. A tag must be one `catalog.IsListed` reports for this release (`i18n/catalog`). `null` clears the choice. Success is `204 No Content`. A missing `language` key is `400 language is required`. An unlisted tag is `400` with the message `server.i18n.unknown_language`, so `args.language` carries the tag sent. 401 when unauthenticated.
+- **GET/PUT `/users/me/preferences`** — the preferences object always carries `language` (`string | null`, `null` when unset). `PUT /users/me/preferences` accepts and ignores a `language` key, so it cannot change the saved language.
+- **POST `/users/me/preferences/reset`** — clears the styling only; the saved language is kept.
+- **GET `/auth/locale`** — public and pre-auth, so it returns only the tag. It reads the config section `i18n`. An absent, unparsable or unlisted default, or a database read failure (logged at warn, never echoed), gives `"en"`.
+
+**Config section `i18n`** (`PUT /admin/config/i18n`): body `{"defaultLanguage": "<tag>"}`. Unknown keys and an empty tag are `422`. A tag that is not offered (missing, or below the completeness threshold) is `400` with `server.i18n.unlisted_language` (`args.language` is the tag). Together with the `notifications` validator below, this is one of the config validators that return a localizable `httperr.Message`; the `put` handler checks `errors.As(*httperr.Message)` before its generic `422` line.
+
+**Config section `notifications`, sink `language`:** optional per sink; validated with `catalog.IsListed`; an unknown tag is `400` with `server.i18n.unknown_language` (`args.language`). Rendering order is sink language, then the instance default language (config section `i18n`), then `en`. `Event` carries the resolved language in an unexported field so the formatter signatures are unchanged.
+
+**Localizable error ids (`api/internal/messages`):** `server.i18n.unknown_language` (`unknown language: {language}`, 400) and `server.i18n.unlisted_language` (`language is not available: {language}`, 400). The registry lives in `internal/messages/messages.go` and `entries_server.go`; the `notify.*` entries live in `internal/notify/messages.go`. Both reach `i18n/locales/en/app.json` through `make i18n-sync`, which runs `messages-export` (both sets) into `i18n-check --sync-server`. Every 4xx `http.Error` in `internal/handlers`, `internal/auth`, `internal/ws` and `internal/rbac` now goes through `httperr.WriteMessage` (registry id) or `httperr.WriteCode` (`server.generic.<status>`, used on the unauthenticated login and OIDC paths and for dynamic messages). Plain-text bodies are byte-identical, and 5xx responses stay `http.Error`. The only 4xx exceptions are the three calls in the `secretName` helper (auth_provider_secret.go, registry_secret.go), which have no request. The migrated ids are in `internal/messages/entries_server.go`, and `internal/messages/usage_test.go` fails when a `messages.New("...")` literal is not registered.
+
+**Problem document negotiation:** a caller that sends `Accept: application/problem+json` gets an RFC 9457 document from `httperr.WriteMessage` / `httperr.WriteCode` with `messageId` (the registry id) and `args`. Every other caller gets the byte-identical plain-text body (`text/plain`, `http.Error` form) that the endpoint has always returned. 5xx responses never carry internal text. The `Message.English` text is the plain body.
+
 ### Error handling
 - **httperr package:** internal errors (K8s 404, DB constraint, FS path) mapped to safe HTTP status + generic message
 - **500+ errors:** never echoed to client; full error logged at Error level server-side
diff --git a/assets/design-export/MANIFEST.md b/assets/design-export/MANIFEST.md
index 06b8a43cd..18121ee50 100644
--- a/assets/design-export/MANIFEST.md
+++ b/assets/design-export/MANIFEST.md
@@ -2550,3 +2550,30 @@ JSON: `Print(JSON.stringify(Get("EkcbF", {depth: 12})))`, `python3 -m json.tool`
 | `ffmEd` | … (New password typed) | New copy of `OC804`. Masked typed value, no remove button, helper "Write-only". |
 
 `Ne5TA` is unaffected. All four have MCP `Get` JSON exports (depth 20, zero elisions; `OC804`/`QFEg9` patched from the prior export with the `Get` result for the changed field subtree) and 2× PNG exports via `Export`. Validated by grepping `Password will be removed` (only `h5clan`) and `Remove password` (`OC804`, `QFEg9`, `h5clan`).
+
+## Spec 019 language pickers and language settings (2026-10-12)
+
+T043, T072 and T094 of `specs/019-localization-language-packs/`. Placement follows OD-015 to OD-017 of that spec.
+
+| Object ID | Name | Change |
+| --- | --- | --- |
+| `Jf27F` | Gameplane/Language Picker Compact | **New** reusable component: lucide `globe`, the native name of the language ("English") and `chevron-down`. 32 px high, no fill and no border. It shows a language name and nothing else. |
+| `CDbjX` | Gameplane/Login Card With Language | **New** reusable component: one instance of `loginCard` (`J14ME`) and an absolute `loginLangRow` (x 0, y 12, 420 wide, right-aligned, 12 px inset) that holds the picker. It exists because `J14ME` cannot take a new child (see the note below). |
+| `N1GkB` | Screen/Login | **Changed.** `loginL` is a new instance of `fjQjb` (`TbEIq`, was `sUdzl`) whose card is swapped for `CDbjX`, so the picker sits in the top-right corner of the card. |
+| `gX7um` | Screen/Login (Light) | **Changed.** Same swap (`gsDFd`, was `UQZOa`). |
+| `g2HLxz` | loginCardError | **Changed.** `loginLangRow` with the picker in the top-right corner. Seen on `jmoi3`. |
+| `ljdA5` | Screen/Login — SSO only | **Changed.** The same row inside the inline card `ohWEp`. |
+| `G7OwqK` | Screen/Login — Language menu open | **New.** Copy of `N1GkB` with the picker's menu open under it (170 px wide, right edges level): English (current, check icon), Français, Deutsch. Native names only. |
+| `HKEl2` | Gameplane/Share Card | **Changed.** `shareLangRow` with the picker in the top-right corner. Seen on every share screen (`C2LQE4`, `q31B6w`, `qFLfB`, `EcoGD`, `epZO2`, `FBiMN`). |
+| `lWvcv` | Screen/Theme Settings | **Changed.** New first card "Language" (`FVPqf`): four radio rows, "Automatic (browser language)", "English" (selected, "100% translated"), "Français" ("100% translated") and "Deutsch" ("86% translated"), then the note "Text that has not been translated yet is shown in English." Frame height 2000 → 2344. |
+| `T1wkiT` | Screen/Theme Settings — Warnings | **Changed.** The same card first (`wPAnz`). Frame height 2146 → 2490. |
+| `g5e2fM` | Screen/Mobile — Theme Settings · Language | **New.** 390 px wide: Mobile TopBar ("Settings"), page header, the settings navigation stacked full width, then the Language card with the same four rows. |
+| `n6Xlo` | Screen/Admin Settings — Notifications | **Changed.** Each sink row has a third line "Language" with a 200 px select ("Français" on ops-discord, "Instance default" on pager). |
+| `eaNkj` | Screen/Admin Settings — Notifications (Add sink) | **New.** Copy of `n6Xlo` with the inline Add sink form open where the "Add sink" button was: Name, Kind, Webhook URL, Language (select "Instance default", helper "Notifications sent to this sink are written in this language."), the six event checkboxes, Cancel and Add sink. The form was not in the design before. |
+| `WZdnw` | Screen/Admin Settings | **Changed.** The General card and a new "Language" card are stacked in a `Panel Column` (`v38YR`). The Language card (`noNHt`) has one select "Default language" set to "English", its helper text and its own Save changes button, because the value is saved to its own config section (`i18n`). |
+
+- **JSON:** `JSON.stringify(Get(id, {depth: 30, includePathGeometry: true}))` for `lWvcv`, `T1wkiT`, `g2HLxz`, `HKEl2`, `ljdA5`, `WZdnw`, `n6Xlo`, `N1GkB`, `gX7um`, `Jf27F`, `CDbjX`, `G7OwqK`, `g5e2fM` and `eaNkj`. Each string was taken from the tool result by a script, never retyped, and its length and FNV-1a hash equal the values computed on the canvas in the same call. Zero `"..."` elisions, `jq empty` passes. Files that were one line stay one line; the others are formatted with `jq .`.
+- **Screenshots:** `Export(ids, "png", …, {scale: 2})` for the 14 ids above and, PNG only, for the screens that show a changed component: `jmoi3`, `C2LQE4`, `q31B6w`, `qFLfB`, `EcoGD`, `epZO2` and `FBiMN`.
+- **Pixel check against the previous PNGs:** `ljdA5`, `g2HLxz`, `HKEl2`, `C2LQE4`, `EcoGD`, `epZO2` and `q31B6w` differ only in the picker's rectangle. `WZdnw` differs only below the General card. `FBiMN` and `qFLfB` also show sub-pixel text anti-aliasing differences. `N1GkB`, `gX7um` and `jmoi3` also show the safe-mode link in the accent colour, and `n6Xlo` also shows the current sidebar ("Clusters") and top bar: the canvas already had both, the previous PNGs were out of date.
+- **Body-text check:** `86% translated` appears only in `lWvcv`, `T1wkiT` and `g5e2fM`; `Notifications sent to this sink are written in this language.` only in `eaNkj`; `Default language for this Gameplane instance.` only in `WZdnw`; `langItemDeutsch` only in `G7OwqK`.
+- **Do not insert a child into `J14ME` through the MCP.** `Insert("J14ME", …)` throws `TypeError: Cannot read properties of undefined (reading 'id')`, and the rollback is not clean: afterwards the two screens with a plain instance of `fjQjb` (`N1GkB`, `gX7um`) showed two login cards and `Get` failed on those instances. `J14ME` is nested in `fjQjb`, and the instances of `fjQjb` on `jmoi3` and `ljdA5` replace that nested card through a children override, which is the likely cause. The two instances were replaced by new ones (so their ids changed) and the picker was added through the wrapper `CDbjX`. `J14ME` (nine children) and `fjQjb` (one child) are unchanged.
diff --git a/assets/design-export/json/CDbjX.json b/assets/design-export/json/CDbjX.json
new file mode 100644
index 000000000..41d31ebd6
--- /dev/null
+++ b/assets/design-export/json/CDbjX.json
@@ -0,0 +1,41 @@
+{
+  "type": "frame",
+  "id": "CDbjX",
+  "x": -10998.0544367535,
+  "y": 27592.997924316056,
+  "name": "Gameplane/Login Card With Language",
+  "reusable": true,
+  "width": 420,
+  "children": [
+    {
+      "id": "g8k7AO",
+      "type": "ref",
+      "ref": "J14ME",
+      "name": "loginCard",
+      "width": "fill_container"
+    },
+    {
+      "type": "frame",
+      "id": "L3y9E",
+      "layoutPosition": "absolute",
+      "x": 0,
+      "y": 12,
+      "name": "loginLangRow",
+      "width": 420,
+      "padding": [
+        0,
+        12
+      ],
+      "justifyContent": "end",
+      "alignItems": "center",
+      "children": [
+        {
+          "id": "c7DCx",
+          "type": "ref",
+          "ref": "Jf27F",
+          "name": "langPicker"
+        }
+      ]
+    }
+  ]
+}
diff --git a/assets/design-export/json/G7OwqK.json b/assets/design-export/json/G7OwqK.json
new file mode 100644
index 000000000..80d0e01dc
--- /dev/null
+++ b/assets/design-export/json/G7OwqK.json
@@ -0,0 +1,114 @@
+{
+  "type": "frame",
+  "id": "G7OwqK",
+  "x": 8200,
+  "y": 4500,
+  "name": "Screen/Login — Language menu open",
+  "theme": {
+    "semantic": "dark"
+  },
+  "clip": true,
+  "width": 1440,
+  "height": 900,
+  "fill": "$background/background",
+  "children": [
+    {
+      "id": "knE8K",
+      "type": "ref",
+      "ref": "fjQjb",
+      "name": "loginL",
+      "width": "fill_container",
+      "height": "fill_container",
+      "children": [
+        {
+          "id": "g5PgR",
+          "type": "ref",
+          "ref": "CDbjX",
+          "name": "loginCard"
+        }
+      ]
+    },
+    {
+      "id": "uERm8",
+      "type": "ref",
+      "ref": "T8Hug",
+      "name": "loginR",
+      "width": "fill_container",
+      "height": "fill_container"
+    },
+    {
+      "type": "frame",
+      "id": "IbjMm",
+      "layoutPosition": "absolute",
+      "x": 388,
+      "y": 184,
+      "name": "langMenu",
+      "width": 170,
+      "fill": "$surface/surface",
+      "cornerRadius": "$radius/md",
+      "stroke": "$border/border",
+      "strokeWidth": 1,
+      "strokeAlignment": "inner",
+      "effect": {
+        "type": "shadow",
+        "shadowType": "outer",
+        "color": "#00000059",
+        "offset": {
+          "x": 0,
+          "y": 4
+        },
+        "blur": 12
+      },
+      "layout": "vertical",
+      "padding": 4,
+      "children": [
+        {
+          "id": "g6idK",
+          "type": "ref",
+          "ref": "B5sYje",
+          "name": "langItemEnglish",
+          "width": "fill_container",
+          "descendants": {
+            "ghUsw": {
+              "icon": "check"
+            },
+            "bpSQ7": {
+              "content": "English",
+              "fontFamily": "$typography/font-sans"
+            }
+          }
+        },
+        {
+          "id": "t5NvrH",
+          "type": "ref",
+          "ref": "W8XiN",
+          "name": "langItemFrancais",
+          "width": "fill_container",
+          "descendants": {
+            "Sr2Q5": {
+              "opacity": 0
+            },
+            "Ra9NK": {
+              "content": "Français"
+            }
+          }
+        },
+        {
+          "id": "ekh8P",
+          "type": "ref",
+          "ref": "W8XiN",
+          "name": "langItemDeutsch",
+          "width": "fill_container",
+          "descendants": {
+            "Sr2Q5": {
+              "opacity": 0
+            },
+            "Ra9NK": {
+              "content": "Deutsch"
+            }
+          }
+        }
+      ]
+    }
+  ]
+}
diff --git a/assets/design-export/json/HKEl2.json b/assets/design-export/json/HKEl2.json
index fbb512018..97cbf687e 100644
--- a/assets/design-export/json/HKEl2.json
+++ b/assets/design-export/json/HKEl2.json
@@ -209,6 +209,29 @@
           "fontWeight": "normal"
         }
       ]
+    },
+    {
+      "type": "frame",
+      "id": "Ukl0w",
+      "layoutPosition": "absolute",
+      "x": 0,
+      "y": 12,
+      "name": "shareLangRow",
+      "width": 440,
+      "padding": [
+        0,
+        12
+      ],
+      "justifyContent": "end",
+      "alignItems": "center",
+      "children": [
+        {
+          "id": "XqZ2v",
+          "type": "ref",
+          "ref": "Jf27F",
+          "name": "langPicker"
+        }
+      ]
     }
   ]
 }
diff --git a/assets/design-export/json/Jf27F.json b/assets/design-export/json/Jf27F.json
new file mode 100644
index 000000000..b3b109c5e
--- /dev/null
+++ b/assets/design-export/json/Jf27F.json
@@ -0,0 +1,48 @@
+{
+  "type": "frame",
+  "id": "Jf27F",
+  "x": -17185,
+  "y": 26315,
+  "name": "Gameplane/Language Picker Compact",
+  "reusable": true,
+  "height": 32,
+  "cornerRadius": "$radius/3xl",
+  "gap": 6,
+  "padding": [
+    6,
+    10
+  ],
+  "alignItems": "center",
+  "children": [
+    {
+      "type": "icon",
+      "id": "G6MTRB",
+      "name": "lpGlobe",
+      "width": 14,
+      "height": 14,
+      "icon": "globe",
+      "library": "lucide",
+      "fill": "$muted"
+    },
+    {
+      "type": "text",
+      "id": "x2Vij",
+      "name": "lpLabel",
+      "fill": "$foreground/foreground",
+      "content": "English",
+      "fontFamily": "$typography/font-sans",
+      "fontSize": 13,
+      "fontWeight": "500"
+    },
+    {
+      "type": "icon",
+      "id": "ZjIo0",
+      "name": "lpChevron",
+      "width": 14,
+      "height": 14,
+      "icon": "chevron-down",
+      "library": "lucide",
+      "fill": "$muted"
+    }
+  ]
+}
diff --git a/assets/design-export/json/N1GkB.json b/assets/design-export/json/N1GkB.json
index 714ec1ed2..1024a638e 100644
--- a/assets/design-export/json/N1GkB.json
+++ b/assets/design-export/json/N1GkB.json
@@ -1 +1 @@
-{"type":"frame","id":"N1GkB","x":1640,"y":4500,"name":"Screen/Login","theme":{"semantic":"dark"},"clip":true,"width":1440,"height":900,"fill":"$background/background","children":[{"id":"sUdzl","type":"ref","ref":"fjQjb","name":"loginL","width":"fill_container","height":"fill_container"},{"id":"X7z8B","type":"ref","ref":"T8Hug","name":"loginR","width":"fill_container","height":"fill_container"}]}
+{"type":"frame","id":"N1GkB","x":1640,"y":4500,"name":"Screen/Login","theme":{"semantic":"dark"},"clip":true,"width":1440,"height":900,"fill":"$background/background","children":[{"id":"TbEIq","type":"ref","ref":"fjQjb","name":"loginL","width":"fill_container","height":"fill_container","children":[{"id":"KTRiy","type":"ref","ref":"CDbjX","name":"loginCard"}]},{"id":"X7z8B","type":"ref","ref":"T8Hug","name":"loginR","width":"fill_container","height":"fill_container"}]}
diff --git a/assets/design-export/json/T1wkiT.json b/assets/design-export/json/T1wkiT.json
index d048a3e03..85cb56d48 100644
--- a/assets/design-export/json/T1wkiT.json
+++ b/assets/design-export/json/T1wkiT.json
@@ -1 +1 @@
-{"type":"frame","id":"T1wkiT","x":43320,"y":-7988,"name":"Screen/Theme Settings — Warnings","theme":{"semantic":"light"},"clip":true,"width":1440,"height":2146,"fill":"$background/background","children":[{"id":"HVdA9","type":"ref","ref":"kKFX9","name":"App Sidebar","height":"fill_container","descendants":{"iTbd8":{"fill":"#00000000"},"iTbd8/ghUsw":{"fill":"$foreground/foreground"},"iTbd8/bpSQ7":{"fill":"$foreground/foreground"},"i8Z1B":{"fill":"#00000000"},"i8Z1B/Sr2Q5":{"fill":"$foreground/foreground"},"i8Z1B/Ra9NK":{"fill":"$foreground/foreground"},"sTSGR":{"fill":"#00000000"},"sTSGR/Sr2Q5":{"fill":"$foreground/foreground"},"sTSGR/Ra9NK":{"fill":"$foreground/foreground"},"NADGL":{"fill":"#00000000"},"NADGL/Sr2Q5":{"fill":"$foreground/foreground"},"NADGL/Ra9NK":{"fill":"$foreground/foreground"},"lZ6pP":{"fill":"#00000000"},"lZ6pP/Sr2Q5":{"fill":"$foreground/foreground"},"lZ6pP/Ra9NK":{"fill":"$foreground/foreground"},"dNsbz":{"fill":"#00000000"},"dNsbz/Sr2Q5":{"fill":"$foreground/foreground"},"dNsbz/Ra9NK":{"fill":"$foreground/foreground"},"uLhzP":{"fill":"#00000000"},"uLhzP/Sr2Q5":{"fill":"$foreground/foreground"},"uLhzP/Ra9NK":{"fill":"$foreground/foreground"},"zV6Z5":{"fill":"#00000000"},"zV6Z5/Sr2Q5":{"fill":"$foreground/foreground"},"zV6Z5/Ra9NK":{"fill":"$foreground/foreground"},"ya5KB":{"fill":"$accent/soft"},"ya5KB/Sr2Q5":{"fill":"$accent/soft-foreground"},"ya5KB/Ra9NK":{"fill":"$accent/soft-foreground"},"q1Xat":{"opacity":"$disabled-opacity"},"q1Xat/Bg6EP":{"fill":"$accent/soft"},"q1Xat/Bg6EP/nMMtW":{"fill":"$accent/soft-foreground"},"q1Xat/icy0X":{"fill":"#00000000"},"q1Xat/icy0X/z3SNRG":{"fill":"$foreground/muted"}}},{"type":"frame","id":"ffffE","name":"Main","width":"fill_container","height":"fill_container","fill":"$background/background","layout":"vertical","children":[{"id":"IB1qY","type":"ref","ref":"gu5WY","name":"Top Bar","width":"fill_container","descendants":{"VzGni":{"type":"frame","id":"evCjB","name":"Breadcrumbs","gap":8,"alignItems":"center","children":[{"type":"text","id":"dlQVv","name":"crumbRoot","fill":"$muted","content":"gameplane","fontFamily":"$typography/font-sans","fontSize":14,"fontWeight":"normal"},{"type":"icon","id":"j4DTP","name":"crumbSep","width":14,"height":14,"icon":"chevron-right","library":"lucide","fill":"$muted"},{"type":"text","id":"DObve","name":"crumbPage","fill":"$foreground/foreground","content":"Settings","fontFamily":"$typography/font-sans","fontSize":14,"fontWeight":"500"}]}}},{"type":"frame","id":"y3RL7i","name":"Body","width":"fill_container","height":"fill_container","layout":"vertical","gap":24,"padding":24,"alignItems":"center","children":[{"id":"BVQxV","type":"ref","ref":"xCDF7","name":"Page Header","width":"fill_container","descendants":{"spCmk":{"content":"Theme & Appearance"},"VbHwU":{"content":"Personal theme presets, colors, custom CSS, and theme portability."},"TgdLz":{"enabled":false}}},{"type":"frame","id":"fQBYE","name":"Settings Layout","width":"fill_container","height":"fill_container","gap":24,"children":[{"id":"O5D0M","type":"ref","ref":"Mp7Ep","name":"Settings Nav","width":220,"descendants":{"eIjoV":{"fill":"#00000000"},"vbQ98":{"fill":"$surface/secondary"}}},{"type":"frame","id":"F5MnIY","name":"Content Column","width":"fill_container","layout":"vertical","gap":16,"children":[{"id":"eT135","type":"ref","ref":"XDZ0E","name":"Card Preset Theme","width":"fill_container","padding":0,"gap":0,"children":[{"id":"DHSP0","type":"ref","ref":"FRpsu","name":"Card Header","width":"fill_container","padding":[20,20,16,20],"gap":4,"descendants":{"fuZHB":{"content":"Preset theme"},"BZG9o":{"content":"Choose the base preset for your dashboard."}}},{"type":"frame","id":"AMv7e","name":"Card Fields","width":"fill_container","layout":"vertical","gap":16,"padding":[0,20,20,20],"children":[{"type":"text","id":"MSijJ","name":"tsPresetsLabel","fill":"$foreground/foreground","content":"Choose a preset theme:","fontFamily":"$typography/font-sans","fontSize":13,"fontWeight":"500"},{"type":"frame","id":"aEsM8","name":"tsPresetRow","width":"fill_container","gap":12,"children":[{"type":"frame","id":"Dyy8o","name":"tsCardPink","width":"fill_container","fill":"$field/background","cornerRadius":10,"stroke":"$border/border","strokeWidth":1,"strokeAlignment":"inner","layout":"vertical","gap":10,"padding":14,"children":[{"id":"x5esx6","type":"ref","ref":"z2mDh","name":"tsCardPink Radio","descendants":{"ocqPf":{"content":"Modern Pink","fontWeight":"500"}}},{"type":"frame","id":"WK1h7","name":"tsCardPink Swatches","gap":8,"children":[{"type":"rectangle","cornerRadius":6,"id":"pjvQ7","name":"tsCardPink Accent Swatch","fill":"#FF4FA3","width":44,"height":26},{"type":"rectangle","cornerRadius":6,"id":"fvgVG","name":"tsCardPink Surface Swatch","fill":"#1C1A20","width":44,"height":26,"stroke":"$border/border","strokeWidth":1,"strokeAlignment":"inner"}]},{"type":"text","id":"AYxqo","name":"tsCardPink Desc","fill":"$muted","content":"Modern HeroUI brand","fontFamily":"$typography/font-sans","fontSize":12,"fontWeight":"normal"}]},{"type":"frame","id":"RWdEP","name":"tsCardLegacy","width":"fill_container","fill":"$field/background","cornerRadius":10,"stroke":"$border/border","strokeWidth":1,"strokeAlignment":"inner","layout":"vertical","gap":10,"padding":14,"children":[{"id":"TFAvJ","type":"ref","ref":"z2mDh","name":"tsCardLegacy Radio","descendants":{"ocqPf":{"content":"Legacy Orange","fontWeight":"500"}}},{"type":"frame","id":"g03Bs","name":"tsCardLegacy Swatches","gap":8,"children":[{"type":"rectangle","cornerRadius":6,"id":"Sp0zw","name":"tsCardLegacy Accent Swatch","fill":"#F97316","width":44,"height":26},{"type":"rectangle","cornerRadius":6,"id":"TBVsa","name":"tsCardLegacy Surface Swatch","fill":"#171717","width":44,"height":26,"stroke":"$border/border","strokeWidth":1,"strokeAlignment":"inner"}]},{"type":"text","id":"CE8fJ","name":"tsCardLegacy Desc","fill":"$muted","content":"Original Gameplane","fontFamily":"$typography/font-sans","fontSize":12,"fontWeight":"normal"}]},{"type":"frame","id":"c9U0a","name":"tsCardCustom","width":"fill_container","fill":"$field/background","cornerRadius":10,"stroke":"$accent/accent","strokeWidth":1,"strokeAlignment":"inner","layout":"vertical","gap":10,"padding":14,"children":[{"id":"f56WXp","type":"ref","ref":"T8ZnV","name":"tsCardCustom Radio","descendants":{"jAx6p":{"content":"Custom colors","fontWeight":"500"}}},{"type":"frame","id":"MWuMt","name":"tsCardCustom Swatches","gap":8,"children":[{"type":"frame","id":"qC9ph","name":"tsCardCustom Accent 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surface","fontFamily":"$typography/font-sans","fontSize":12,"fontWeight":"normal"}]}]},{"type":"frame","id":"TGnpT","name":"tsRetentionNote","width":"fill_container","gap":8,"alignItems":"center","children":[{"type":"icon","id":"UQizl","name":"tsNoteIcon","width":14,"height":14,"icon":"info","library":"lucide","fill":"$muted"},{"type":"text","id":"A0vl9","name":"tsNoteText","fill":"$muted","content":"Your custom colors and CSS are kept and can be re-applied later.","fontFamily":"$typography/font-sans","fontSize":12,"fontWeight":"normal"}]}]}]},{"id":"pd4tf","type":"ref","ref":"XDZ0E","name":"Card Appearance Mode","width":"fill_container","padding":0,"gap":0,"children":[{"id":"Yfzhs","type":"ref","ref":"FRpsu","name":"Card Header","width":"fill_container","padding":[20,20,16,20],"gap":4,"descendants":{"fuZHB":{"content":"Appearance mode"},"BZG9o":{"content":"Light, dark, or follow your system preference."}}},{"type":"frame","id":"ceIti","name":"Card 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color","fontFamily":"$typography/font-sans","fontSize":12,"fontWeight":"normal"}]}]}]},{"id":"ffLVD","type":"ref","ref":"XDZ0E","name":"Card Custom Colors","width":"fill_container","padding":0,"gap":0,"children":[{"id":"dCYbw","type":"ref","ref":"FRpsu","name":"Card Header","width":"fill_container","padding":[20,20,16,20],"gap":4,"descendants":{"fuZHB":{"content":"Custom colors"},"BZG9o":{"content":"Accent color and surface tone for the dashboard."}}},{"type":"frame","id":"u3VzxL","name":"Card Fields","width":"fill_container","layout":"vertical","gap":16,"padding":[0,20,20,20],"children":[{"type":"frame","id":"GpVGU","name":"ccSwatches","gap":10,"alignItems":"center","children":[{"type":"rectangle","cornerRadius":6,"id":"muTX2","name":"ccSwatch Blue","fill":"#3B82F6","width":28,"height":28,"stroke":"$border/border","strokeWidth":1,"strokeAlignment":"inner"},{"type":"rectangle","cornerRadius":6,"id":"OHbAi","name":"ccSwatch Emerald","fill":"#10B981","width":28,"height":28,"stroke":"$border/border","strokeWidth":1,"strokeAlignment":"inner"},{"type":"rectangle","cornerRadius":6,"id":"sazSN","name":"ccSwatch Purple","fill":"#8B5CF6","width":28,"height":28,"stroke":"$border/border","strokeWidth":1,"strokeAlignment":"inner"},{"type":"rectangle","cornerRadius":6,"id":"BKkk5","name":"ccSwatch Amber","fill":"#F59E0B","width":28,"height":28,"stroke":"$foreground/foreground","strokeWidth":2,"strokeAlignment":"inner"},{"type":"rectangle","cornerRadius":6,"id":"cLP2e","name":"ccSwatch Cyan","fill":"#06B6D4","width":28,"height":28,"stroke":"$border/border","strokeWidth":1,"strokeAlignment":"inner"},{"type":"rectangle","cornerRadius":6,"id":"S2GNs","name":"ccSwatch Rose","fill":"#F43F5E","width":28,"height":28,"stroke":"$border/border","strokeWidth":1,"strokeAlignment":"inner"},{"type":"rectangle","cornerRadius":6,"id":"IDtRg","name":"ccSwatch 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Choose a darker accent or a darker surface tone."},"c0FRXZ":{"type":"frame","id":"ysuO2","x":0,"y":0,"name":"hiddenAction","enabled":false,"width":0,"height":0}}}]}]},{"id":"UizTK","type":"ref","ref":"XDZ0E","name":"Card Custom CSS","width":"fill_container","padding":0,"gap":0,"children":[{"id":"a1nyR","type":"ref","ref":"FRpsu","name":"Card Header","width":"fill_container","padding":[20,20,16,20],"gap":4,"descendants":{"fuZHB":{"content":"Custom CSS overlay"},"BZG9o":{"content":"A stylesheet layered on top of the active base theme."}}},{"type":"frame","id":"y6Qp3a","name":"Card Fields","width":"fill_container","layout":"vertical","gap":16,"padding":[0,20,20,20],"children":[{"type":"frame","id":"K23hg","name":"cssToggleRow","width":"fill_container","gap":10,"alignItems":"center","children":[{"id":"S8J6G","type":"ref","ref":"hl7R3","name":"cssToggle"},{"type":"text","id":"dv7Ad","name":"cssToggleLabel","fill":"$foreground/foreground","content":"Enable custom CSS overlay","fontFamily":"$typography/font-sans","fontSize":14,"fontWeight":"500"}]},{"type":"text","id":"N7jWQ","name":"cssHelper","fill":"$muted","textGrowth":"fixed-width","width":"fill_container","content":"Your rules are applied on top of the active base theme and win over it; elements you don't target follow the base theme.","lineHeight":1.5,"fontFamily":"$typography/font-sans","fontSize":12,"fontWeight":"normal"},{"id":"VdHjg","type":"ref","ref":"rqAWk","name":"cssTextarea","width":"fill_container","descendants":{"Nw6da":{"content":"Custom CSS"},"cbBhZ":{"height":140},"CcOQD":{"content":"/* Example: customize typography or borders */\n:root {\n  --radius: 14px;\n}","fontFamily":"$typography/font-mono","fontSize":12,"lineHeight":1.6},"e3p2I":{"content":"128 / 32,768"}}},{"type":"frame","id":"o1h94j","name":"cssErrorRow","width":"fill_container","gap":8,"alignItems":"center","children":[{"type":"icon","id":"W9VD3C","name":"cssErrorIcon","width":14,"height":14,"icon":"circle-alert","library":"lucide","fill":"$danger/danger"},{"type":"text","id":"N4GsdW","name":"cssErrorText","fill":"$danger/danger","content":"External resource loads are not allowed (line 4: `@import url('https://example.com/theme.css');`). Paste the content inline instead.","fontFamily":"$typography/font-sans","fontSize":12,"fontWeight":"normal"}]},{"id":"giS8X","type":"ref","ref":"Llzos","name":"cssWarning","width":"fill_container","descendants":{"sINBP":{"icon":"triangle-alert"},"BXuYr":{"content":"Custom CSS recovery"},"JmFhb":{"content":"Custom CSS modifies application appearance directly. If the interface becomes unusable, recover via the ?safe-mode=1 URL parameter, the safe-mode keyboard shortcut, or the 'Sign in with safe mode' link on the login page."},"c0FRXZ":{"type":"frame","id":"wzOUH","x":0,"y":0,"name":"hiddenAction","enabled":false,"width":0,"height":0}}}]}]},{"id":"d17I0K","type":"ref","ref":"XDZ0E","name":"Card Export Import","width":"fill_container","padding":0,"gap":0,"children":[{"id":"O9qWLm","type":"ref","ref":"FRpsu","name":"Card Header","width":"fill_container","padding":[20,20,16,20],"gap":4,"descendants":{"fuZHB":{"content":"Export / Import"},"BZG9o":{"content":"Copy or download your saved theme profile, or apply a gameplane-theme v1 document."}}},{"type":"frame","id":"EdiRJ","name":"Card Fields","width":"fill_container","layout":"vertical","gap":16,"padding":[0,20,20,20],"children":[{"type":"frame","id":"i1sQhx","name":"exButtonRow","gap":8,"alignItems":"center","children":[{"id":"OVNyJ","type":"ref","ref":"rNhll","name":"exBtnCopy","descendants":{"wDXFJ/K8d1zg":{"icon":"copy"},"wDXFJ/zMNkR":{"content":"Copy to clipboard"}}},{"id":"ohzv5","type":"ref","ref":"rNhll","name":"exBtnDownload","descendants":{"wDXFJ/K8d1zg":{"icon":"download"},"wDXFJ/zMNkR":{"content":"Download gameplane-theme.json"}}}]},{"id":"i9jFX","type":"ref","ref":"rqAWk","name":"imPasteArea","width":"fill_container","descendants":{"Nw6da":{"content":"Paste theme JSON"},"CcOQD":{"content":"Paste a gameplane-theme v1 document…"},"e3p2I":{"content":"Accepts gameplane-theme v1 documents."}}},{"type":"frame","id":"sX3XQ","name":"imFileRow","gap":10,"alignItems":"center","children":[{"id":"ZjTig","type":"ref","ref":"rNhll","name":"imBtnChooseFile","descendants":{"wDXFJ/K8d1zg":{"icon":"upload"},"wDXFJ/zMNkR":{"content":"Choose file…"}}},{"type":"text","id":"k6mXE6","name":"imFileHint","fill":"$muted","content":"Accepts gameplane-theme v1 (.json)","fontFamily":"$typography/font-sans","fontSize":12,"fontWeight":"normal"}]},{"type":"frame","id":"TqyKS","name":"imPreviewCard","width":"fill_container","fill":"$field/background","cornerRadius":10,"stroke":"$border/border","strokeWidth":1,"strokeAlignment":"inner","layout":"vertical","gap":8,"padding":12,"children":[{"type":"text","id":"fagrL","name":"imPreviewTitle","fill":"$foreground/foreground","content":"Import preview","fontFamily":"$typography/font-sans","fontSize":13,"fontWeight":"500"},{"type":"frame","id":"t8rWy","name":"imPresetRow","gap":8,"alignItems":"center","children":[{"type":"rectangle","cornerRadius":4,"id":"qPLcw","name":"imAccentSwatch","fill":"#FF4FA3","width":16,"height":16},{"type":"text","id":"QsddR","name":"imPresetName","fill":"$foreground/foreground","content":"Preset: Modern Pink","fontFamily":"$typography/font-sans","fontSize":12,"fontWeight":"normal"}]},{"type":"text","id":"MPOfu","name":"imCssSize","fill":"$muted","content":"Custom CSS: 1,204 bytes","fontFamily":"$typography/font-sans","fontSize":12,"fontWeight":"normal"},{"type":"frame","id":"C20PIa","name":"imApplyRow","width":"fill_container","justifyContent":"end","children":[{"id":"oeLpO","type":"ref","ref":"tpKRk","name":"imBtnApply","descendants":{"q58In/Xpn7K":{"enabled":false},"q58In/U6q13B":{"content":"Apply import"}}}]}]},{"type":"frame","id":"pCN2A","name":"imScopeNote","width":"fill_container","gap":8,"alignItems":"center","children":[{"type":"icon","id":"k6QN4x","name":"imScopeIcon","width":14,"height":14,"icon":"info","library":"lucide","fill":"$muted"},{"type":"text","id":"UITBY","name":"imScopeText","fill":"$muted","content":"Sharing galleries and organization-enforced themes are not part of this feature.","fontFamily":"$typography/font-sans","fontSize":12,"fontWeight":"normal"}]}]}]},{"type":"frame","id":"pqHRF","name":"tsActionsRow","width":"fill_container","padding":[8,0,0,0],"justifyContent":"space_between","alignItems":"center","children":[{"id":"AK6BN","type":"ref","ref":"XoX7L","name":"tsBtnReset","descendants":{"dyD7Z":{"icon":"rotate-ccw"},"C8QRt/t8p1M2":{"content":"Reset to Defaults"}}},{"id":"oQE4k","type":"ref","ref":"tpKRk","name":"tsBtnSave","descendants":{"q58In/Xpn7K":{"enabled":false},"q58In/U6q13B":{"content":"Save"}}}]}]}]}]}]}]}
diff --git a/assets/design-export/json/WZdnw.json b/assets/design-export/json/WZdnw.json
index 9a4d3d418..0240ce61a 100644
--- a/assets/design-export/json/WZdnw.json
+++ b/assets/design-export/json/WZdnw.json
@@ -164,127 +164,166 @@
                   "width": 220
                 },
                 {
-                  "id": "l4Iw3z",
-                  "type": "ref",
-                  "ref": "XDZ0E",
-                  "name": "Settings Panel",
+                  "type": "frame",
+                  "id": "v38YR",
+                  "name": "Panel Column",
                   "width": "fill_container",
-                  "padding": 0,
-                  "gap": 0,
+                  "layout": "vertical",
+                  "gap": 24,
                   "children": [
                     {
-                      "id": "tXDnN",
+                      "id": "l4Iw3z",
                       "type": "ref",
-                      "ref": "FRpsu",
-                      "name": "Card Header",
+                      "ref": "XDZ0E",
+                      "name": "Settings Panel",
                       "width": "fill_container",
-                      "padding": [
-                        20,
-                        20,
-                        16,
-                        20
-                      ],
-                      "gap": 4,
-                      "descendants": {
-                        "fuZHB": {
-                          "content": "General"
-                        },
-                        "BZG9o": {
-                          "content": "Basic identity for this Gameplane instance."
-                        }
-                      }
-                    },
-                    {
-                      "type": "frame",
-                      "id": "DI9X5",
-                      "name": "Card Fields",
-                      "width": "fill_container",
-                      "layout": "vertical",
-                      "gap": 16,
-                      "padding": [
-                        0,
-                        20
-                      ],
+                      "padding": 0,
+                      "gap": 0,
                       "children": [
                         {
-                          "type": "frame",
-                          "id": "BGqdF",
-                          "name": "fieldInstanceName",
+                          "id": "tXDnN",
+                          "type": "ref",
+                          "ref": "FRpsu",
+                          "name": "Card Header",
                           "width": "fill_container",
-                          "layout": "vertical",
-                          "children": [
-                            {
-                              "id": "E8BwC",
-                              "type": "ref",
-                              "ref": "aRqX6",
-                              "name": "Input/Primary",
-                              "width": "fill_container",
-                              "descendants": {
-                                "ANxU1": {
-                                  "content": "Instance name"
-                                },
-                                "hokJ3": {
-                                  "content": "",
-                                  "fill": "$field/placeholder"
-                                },
-                                "wolxN": {
-                                  "content": "Optional. Names this install on the Cluster page and in notifications."
-                                }
-                              }
+                          "padding": [
+                            20,
+                            20,
+                            16,
+                            20
+                          ],
+                          "gap": 4,
+                          "descendants": {
+                            "fuZHB": {
+                              "content": "General"
+                            },
+                            "BZG9o": {
+                              "content": "Basic identity for this Gameplane instance."
                             }
-                          ]
+                          }
                         },
                         {
                           "type": "frame",
-                          "id": "yjujL",
-                          "name": "fieldExternalURL",
+                          "id": "DI9X5",
+                          "name": "Card Fields",
                           "width": "fill_container",
                           "layout": "vertical",
+                          "gap": 16,
+                          "padding": [
+                            0,
+                            20
+                          ],
                           "children": [
                             {
-                              "id": "YesmO",
-                              "type": "ref",
-                              "ref": "aRqX6",
-                              "name": "Input/Primary",
+                              "type": "frame",
+                              "id": "BGqdF",
+                              "name": "fieldInstanceName",
                               "width": "fill_container",
-                              "descendants": {
-                                "ANxU1": {
-                                  "content": "External URL"
-                                },
-                                "hokJ3": {
-                                  "content": "",
-                                  "fill": "$field/placeholder"
-                                },
-                                "wolxN": {
-                                  "content": "Canonical base URL, used in emails, webhooks, OIDC callbacks."
+                              "layout": "vertical",
+                              "children": [
+                                {
+                                  "id": "E8BwC",
+                                  "type": "ref",
+                                  "ref": "aRqX6",
+                                  "name": "Input/Primary",
+                                  "width": "fill_container",
+                                  "descendants": {
+                                    "ANxU1": {
+                                      "content": "Instance name"
+                                    },
+                                    "hokJ3": {
+                                      "content": "",
+                                      "fill": "$field/placeholder"
+                                    },
+                                    "wolxN": {
+                                      "content": "Optional. Names this install on the Cluster page and in notifications."
+                                    }
+                                  }
                                 }
-                              }
+                              ]
+                            },
+                            {
+                              "type": "frame",
+                              "id": "yjujL",
+                              "name": "fieldExternalURL",
+                              "width": "fill_container",
+                              "layout": "vertical",
+                              "children": [
+                                {
+                                  "id": "YesmO",
+                                  "type": "ref",
+                                  "ref": "aRqX6",
+                                  "name": "Input/Primary",
+                                  "width": "fill_container",
+                                  "descendants": {
+                                    "ANxU1": {
+                                      "content": "External URL"
+                                    },
+                                    "hokJ3": {
+                                      "content": "",
+                                      "fill": "$field/placeholder"
+                                    },
+                                    "wolxN": {
+                                      "content": "Canonical base URL, used in emails, webhooks, OIDC callbacks."
+                                    }
+                                  }
+                                }
+                              ]
+                            },
+                            {
+                              "type": "frame",
+                              "id": "l6wE1E",
+                              "name": "fieldDefaultNamespace",
+                              "width": "fill_container",
+                              "layout": "vertical",
+                              "children": [
+                                {
+                                  "id": "SVLor",
+                                  "type": "ref",
+                                  "ref": "aRqX6",
+                                  "name": "Input/Primary",
+                                  "width": "fill_container",
+                                  "descendants": {
+                                    "ANxU1": {
+                                      "content": "Default namespace"
+                                    },
+                                    "hokJ3": {
+                                      "content": "gameplane-games",
+                                      "fill": "$foreground/foreground"
+                                    },
+                                    "wolxN": {
+                                      "content": "Where new GameServers land by default."
+                                    }
+                                  }
+                                }
+                              ]
                             }
                           ]
                         },
                         {
                           "type": "frame",
-                          "id": "l6wE1E",
-                          "name": "fieldDefaultNamespace",
+                          "id": "Aey03",
+                          "name": "Card Actions",
                           "width": "fill_container",
-                          "layout": "vertical",
+                          "padding": [
+                            8,
+                            20,
+                            20,
+                            20
+                          ],
+                          "justifyContent": "end",
                           "children": [
                             {
-                              "id": "SVLor",
+                              "id": "KmwSz",
                               "type": "ref",
-                              "ref": "aRqX6",
-                              "name": "Input/Primary",
-                              "width": "fill_container",
+                              "ref": "tpKRk",
+                              "name": "Btn Save Changes",
                               "descendants": {
-                                "ANxU1": {
-                                  "content": "Default namespace"
-                                },
-                                "hokJ3": {
-                                  "content": "gameplane-games",
-                                  "fill": "$foreground/foreground"
+                                "q58In/Xpn7K": {
+                                  "enabled": false
                                 },
-                                "wolxN": {
-                                  "content": "Where new GameServers land by default."
+                                "q58In/U6q13B": {
+                                  "content": "Save changes"
                                 }
                               }
                             }
@@ -293,31 +332,138 @@
                       ]
                     },
                     {
-                      "type": "frame",
-                      "id": "Aey03",
-                      "name": "Card Actions",
+                      "id": "noNHt",
+                      "type": "ref",
+                      "ref": "XDZ0E",
+                      "name": "Language Panel",
                       "width": "fill_container",
-                      "padding": [
-                        8,
-                        20,
-                        20,
-                        20
-                      ],
-                      "justifyContent": "end",
+                      "padding": 0,
+                      "gap": 0,
                       "children": [
                         {
-                          "id": "KmwSz",
+                          "id": "F1k5Xe",
                           "type": "ref",
-                          "ref": "tpKRk",
-                          "name": "Btn Save Changes",
+                          "ref": "FRpsu",
+                          "name": "Card Header",
+                          "width": "fill_container",
+                          "padding": [
+                            20,
+                            20,
+                            16,
+                            20
+                          ],
+                          "gap": 4,
                           "descendants": {
-                            "q58In/Xpn7K": {
-                              "enabled": false
+                            "fuZHB": {
+                              "content": "Language"
                             },
-                            "q58In/U6q13B": {
-                              "content": "Save changes"
+                            "BZG9o": {
+                              "content": "Default language for this Gameplane instance.",
+                              "textGrowth": "fixed-width",
+                              "width": "fill_container"
                             }
                           }
+                        },
+                        {
+                          "type": "frame",
+                          "id": "m1Yjkf",
+                          "name": "Card Fields",
+                          "width": "fill_container",
+                          "layout": "vertical",
+                          "gap": 16,
+                          "padding": [
+                            0,
+                            20
+                          ],
+                          "children": [
+                            {
+                              "type": "frame",
+                              "id": "F8NpG0",
+                              "name": "fieldDefaultLanguage",
+                              "width": "fill_container",
+                              "layout": "vertical",
+                              "gap": 4,
+                              "children": [
+                                {
+                                  "type": "text",
+                                  "id": "VVbzH",
+                                  "name": "defaultLanguageLabel",
+                                  "fill": "$foreground/foreground",
+                                  "content": "Default language",
+                                  "fontFamily": "$typography/font-sans",
+                                  "fontSize": 14,
+                                  "fontWeight": "500"
+                                },
+                                {
+                                  "id": "hnojD",
+                                  "type": "ref",
+                                  "ref": "AT7ya",
+                                  "name": "defaultLanguageSelect",
+                                  "width": "fill_container",
+                                  "height": 40,
+                                  "descendants": {
+                                    "cFsFk": {
+                                      "content": "English",
+                                      "fill": "$foreground/foreground"
+                                    }
+                                  }
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "o7JIu4",
+                                  "name": "defaultLanguageHintWrap",
+                                  "width": "fill_container",
+                                  "padding": [
+                                    0,
+                                    4
+                                  ],
+                                  "children": [
+                                    {
+                                      "type": "text",
+                                      "id": "kNjLO",
+                                      "name": "defaultLanguageHint",
+                                      "fill": "$muted",
+                                      "textGrowth": "fixed-width",
+                                      "width": "fill_container",
+                                      "content": "Used when someone has not chosen a language and none of their browser's languages are available. Notification sinks set to Instance default use it too.",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 12,
+                                      "fontWeight": "normal"
+                                    }
+                                  ]
+                                }
+                              ]
+                            }
+                          ]
+                        },
+                        {
+                          "type": "frame",
+                          "id": "jfCH4",
+                          "name": "Card Actions",
+                          "width": "fill_container",
+                          "padding": [
+                            8,
+                            20,
+                            20,
+                            20
+                          ],
+                          "justifyContent": "end",
+                          "children": [
+                            {
+                              "id": "EhcS9",
+                              "type": "ref",
+                              "ref": "tpKRk",
+                              "name": "Btn Save Changes",
+                              "descendants": {
+                                "q58In/Xpn7K": {
+                                  "enabled": false
+                                },
+                                "q58In/U6q13B": {
+                                  "content": "Save changes"
+                                }
+                              }
+                            }
+                          ]
                         }
                       ]
                     }
diff --git a/assets/design-export/json/eaNkj.json b/assets/design-export/json/eaNkj.json
new file mode 100644
index 000000000..3e3b6c84a
--- /dev/null
+++ b/assets/design-export/json/eaNkj.json
@@ -0,0 +1,991 @@
+{
+  "type": "frame",
+  "id": "eaNkj",
+  "x": 9840,
+  "y": 23015,
+  "name": "Screen/Admin Settings — Notifications (Add sink)",
+  "theme": {
+    "semantic": "dark"
+  },
+  "clip": true,
+  "width": 1440,
+  "height": 965,
+  "fill": "$background/background",
+  "children": [
+    {
+      "id": "doJV6",
+      "type": "ref",
+      "ref": "kKFX9",
+      "height": "fill_container",
+      "descendants": {
+        "iTbd8": {
+          "fill": "#00000000"
+        },
+        "iTbd8/ghUsw": {
+          "fill": "$foreground/foreground"
+        },
+        "iTbd8/bpSQ7": {
+          "fill": "$foreground/foreground"
+        },
+        "ya5KB": {
+          "fill": "$accent/soft"
+        },
+        "ya5KB/Sr2Q5": {
+          "fill": "$accent/soft-foreground"
+        },
+        "ya5KB/Ra9NK": {
+          "fill": "$accent/soft-foreground"
+        }
+      }
+    },
+    {
+      "type": "frame",
+      "id": "wGYxe",
+      "name": "Main",
+      "width": "fill_container",
+      "height": "fill_container",
+      "fill": "$background/background",
+      "layout": "vertical",
+      "children": [
+        {
+          "id": "KI26C",
+          "type": "ref",
+          "ref": "gu5WY",
+          "width": "fill_container",
+          "descendants": {
+            "Gl7AY": {
+              "content": "Settings"
+            }
+          }
+        },
+        {
+          "type": "frame",
+          "id": "D8np3C",
+          "name": "Body",
+          "width": "fill_container",
+          "height": "fill_container",
+          "layout": "vertical",
+          "gap": 24,
+          "padding": 24,
+          "children": [
+            {
+              "id": "qbpRF",
+              "type": "ref",
+              "ref": "xCDF7",
+              "width": "fill_container",
+              "descendants": {
+                "spCmk": {
+                  "content": "Admin settings"
+                },
+                "VbHwU": {
+                  "content": "Platform-wide configuration for this Gameplane instance."
+                },
+                "TgdLz": {
+                  "enabled": false
+                }
+              }
+            },
+            {
+              "type": "frame",
+              "id": "k0Dnil",
+              "name": "Settings Layout",
+              "width": "fill_container",
+              "height": "fill_container",
+              "gap": 24,
+              "children": [
+                {
+                  "id": "Xzvj6",
+                  "type": "ref",
+                  "ref": "Mp7Ep",
+                  "name": "Settings Nav",
+                  "width": 220,
+                  "descendants": {
+                    "eIjoV": {
+                      "fill": "#00000000"
+                    },
+                    "KSTX4": {
+                      "fill": "$surface/secondary"
+                    }
+                  }
+                },
+                {
+                  "id": "QvCbe",
+                  "type": "ref",
+                  "ref": "XDZ0E",
+                  "name": "Settings Panel",
+                  "width": "fill_container",
+                  "padding": 0,
+                  "gap": 0,
+                  "cornerRadius": 10,
+                  "height": "fit_content",
+                  "clip": false,
+                  "children": [
+                    {
+                      "id": "UyGwr",
+                      "type": "ref",
+                      "ref": "FRpsu",
+                      "width": "fill_container",
+                      "padding": [
+                        20,
+                        20,
+                        16,
+                        20
+                      ],
+                      "descendants": {
+                        "fuZHB": {
+                          "content": "Notifications"
+                        },
+                        "BZG9o": {
+                          "content": "Deliver server health and backup/restore events to Discord, Slack, ntfy, email, or webhooks. Credentials are entered when adding a sink and stored as a labelled Secret in the control-plane namespace.",
+                          "textGrowth": "fixed-width",
+                          "width": "fill_container"
+                        }
+                      }
+                    },
+                    {
+                      "id": "XXRhs",
+                      "type": "ref",
+                      "ref": "I9ZPb",
+                      "width": "fill_container",
+                      "padding": [
+                        0,
+                        20
+                      ],
+                      "gap": 16,
+                      "children": [
+                        {
+                          "type": "frame",
+                          "id": "CBFXu",
+                          "name": "sinkList",
+                          "width": "fill_container",
+                          "layout": "vertical",
+                          "children": [
+                            {
+                              "type": "frame",
+                              "id": "SVk9G",
+                              "name": "sinkDiscord",
+                              "width": "fill_container",
+                              "stroke": "$border/border",
+                              "strokeWidth": {
+                                "bottom": 1
+                              },
+                              "strokeAlignment": "inner",
+                              "gap": 12,
+                              "padding": [
+                                12,
+                                0
+                              ],
+                              "alignItems": "center",
+                              "children": [
+                                {
+                                  "type": "frame",
+                                  "id": "Evfhj",
+                                  "name": "iconBox",
+                                  "width": 32,
+                                  "height": 32,
+                                  "fill": "$surface/secondary",
+                                  "cornerRadius": 6,
+                                  "justifyContent": "center",
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "type": "icon",
+                                      "id": "b6H8ig",
+                                      "width": 16,
+                                      "height": 16,
+                                      "icon": "messages-square",
+                                      "library": "lucide",
+                                      "fill": "$muted"
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "hWFRx",
+                                  "width": "fill_container",
+                                  "layout": "vertical",
+                                  "gap": 2,
+                                  "children": [
+                                    {
+                                      "type": "text",
+                                      "id": "NgjDB",
+                                      "fill": "$foreground/foreground",
+                                      "content": "ops-discord",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 14,
+                                      "fontWeight": "normal"
+                                    },
+                                    {
+                                      "type": "text",
+                                      "id": "O2W4ag",
+                                      "fill": "$muted",
+                                      "content": "discord · Secret: gameplane-notify-ops-discord",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 12,
+                                      "fontWeight": "normal"
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "uSrNK",
+                                      "name": "sinkLangRow",
+                                      "gap": 8,
+                                      "padding": [
+                                        6,
+                                        0,
+                                        0,
+                                        0
+                                      ],
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "xhp4w",
+                                          "name": "sinkLangLabel",
+                                          "fill": "$muted",
+                                          "content": "Language",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        },
+                                        {
+                                          "id": "slRXb",
+                                          "type": "ref",
+                                          "ref": "AT7ya",
+                                          "name": "sinkLangSelect",
+                                          "width": 200,
+                                          "height": 32,
+                                          "padding": [
+                                            6,
+                                            10
+                                          ],
+                                          "descendants": {
+                                            "cFsFk": {
+                                              "content": "Français",
+                                              "fill": "$foreground/foreground",
+                                              "fontSize": 13
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "shS0o",
+                                  "name": "eventChips",
+                                  "gap": 6,
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "type": "frame",
+                                      "id": "YjgGY",
+                                      "fill": "$surface/secondary",
+                                      "cornerRadius": 999,
+                                      "padding": [
+                                        2,
+                                        8
+                                      ],
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "pLL6W",
+                                          "fill": "$muted",
+                                          "content": "server.unhealthy",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 11,
+                                          "fontWeight": "normal"
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "ktWDA",
+                                      "fill": "$surface/secondary",
+                                      "cornerRadius": 999,
+                                      "padding": [
+                                        2,
+                                        8
+                                      ],
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "xMeNr",
+                                          "fill": "$muted",
+                                          "content": "backup.failed",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 11,
+                                          "fontWeight": "normal"
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "o5o23",
+                                      "fill": "$surface/secondary",
+                                      "cornerRadius": 999,
+                                      "padding": [
+                                        2,
+                                        8
+                                      ],
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "S863wb",
+                                          "fill": "$muted",
+                                          "content": "+2",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 11,
+                                          "fontWeight": "normal"
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                },
+                                {
+                                  "id": "I97xSL",
+                                  "type": "ref",
+                                  "ref": "FIB65",
+                                  "name": "btnSendTest",
+                                  "height": 32,
+                                  "descendants": {
+                                    "K8d1zg": {
+                                      "enabled": false
+                                    },
+                                    "zMNkR": {
+                                      "content": "Send test"
+                                    }
+                                  }
+                                },
+                                {
+                                  "id": "bWyjr",
+                                  "type": "ref",
+                                  "ref": "hl7R3",
+                                  "name": "switchOn"
+                                },
+                                {
+                                  "id": "TCPlY",
+                                  "type": "ref",
+                                  "ref": "j9sz4",
+                                  "name": "btnDelete",
+                                  "width": 36,
+                                  "height": 36,
+                                  "descendants": {
+                                    "uQ9KQ": {
+                                      "icon": "trash-2"
+                                    }
+                                  }
+                                }
+                              ]
+                            },
+                            {
+                              "type": "frame",
+                              "id": "d7SXt",
+                              "name": "sinkWebhook",
+                              "width": "fill_container",
+                              "gap": 12,
+                              "padding": [
+                                12,
+                                0
+                              ],
+                              "alignItems": "center",
+                              "children": [
+                                {
+                                  "type": "frame",
+                                  "id": "k8ZNTa",
+                                  "name": "iconBox",
+                                  "width": 32,
+                                  "height": 32,
+                                  "fill": "$surface/secondary",
+                                  "cornerRadius": 6,
+                                  "justifyContent": "center",
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "type": "icon",
+                                      "id": "bcpTb",
+                                      "width": 16,
+                                      "height": 16,
+                                      "icon": "webhook",
+                                      "library": "lucide",
+                                      "fill": "$muted"
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "HEcy8",
+                                  "width": "fill_container",
+                                  "layout": "vertical",
+                                  "gap": 2,
+                                  "children": [
+                                    {
+                                      "type": "text",
+                                      "id": "TKSOK",
+                                      "fill": "$foreground/foreground",
+                                      "content": "pager",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 14,
+                                      "fontWeight": "normal"
+                                    },
+                                    {
+                                      "type": "text",
+                                      "id": "R3i4Q",
+                                      "fill": "$muted",
+                                      "content": "webhook · no Secret configured",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 12,
+                                      "fontWeight": "normal"
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "ry01M",
+                                      "name": "sinkLangRow",
+                                      "gap": 8,
+                                      "padding": [
+                                        6,
+                                        0,
+                                        0,
+                                        0
+                                      ],
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "mXwqf",
+                                          "name": "sinkLangLabel",
+                                          "fill": "$muted",
+                                          "content": "Language",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        },
+                                        {
+                                          "id": "a9PBm",
+                                          "type": "ref",
+                                          "ref": "AT7ya",
+                                          "name": "sinkLangSelect",
+                                          "width": 200,
+                                          "height": 32,
+                                          "padding": [
+                                            6,
+                                            10
+                                          ],
+                                          "descendants": {
+                                            "cFsFk": {
+                                              "content": "Instance default",
+                                              "fill": "$foreground/foreground",
+                                              "fontSize": 13
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "E39TY",
+                                  "name": "needsSecret",
+                                  "fill": "$warning/soft",
+                                  "cornerRadius": 999,
+                                  "padding": [
+                                    2,
+                                    8
+                                  ],
+                                  "justifyContent": "center",
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "type": "text",
+                                      "id": "bD8Rq",
+                                      "fill": "$warning/soft-foreground",
+                                      "content": "Needs secret",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 11,
+                                      "fontWeight": "500"
+                                    }
+                                  ]
+                                },
+                                {
+                                  "id": "Tgujm",
+                                  "type": "ref",
+                                  "ref": "FIB65",
+                                  "name": "btnSendTest",
+                                  "height": 32,
+                                  "opacity": 0.5,
+                                  "descendants": {
+                                    "K8d1zg": {
+                                      "enabled": false
+                                    },
+                                    "zMNkR": {
+                                      "content": "Send test"
+                                    }
+                                  }
+                                },
+                                {
+                                  "id": "tyv3s",
+                                  "type": "ref",
+                                  "ref": "rh2QH",
+                                  "name": "switchOff"
+                                },
+                                {
+                                  "id": "ZD2ij",
+                                  "type": "ref",
+                                  "ref": "j9sz4",
+                                  "name": "btnDelete",
+                                  "width": 36,
+                                  "height": 36,
+                                  "descendants": {
+                                    "uQ9KQ": {
+                                      "icon": "trash-2"
+                                    }
+                                  }
+                                }
+                              ]
+                            }
+                          ]
+                        },
+                        {
+                          "type": "frame",
+                          "id": "n7Y8N9",
+                          "name": "addSinkForm",
+                          "width": "fill_container",
+                          "fill": "$surface/surface",
+                          "cornerRadius": 8,
+                          "stroke": "$border/border",
+                          "strokeWidth": 1,
+                          "strokeAlignment": "inner",
+                          "layout": "vertical",
+                          "gap": 12,
+                          "padding": 16,
+                          "children": [
+                            {
+                              "type": "text",
+                              "id": "ZSGfk",
+                              "name": "addSinkTitle",
+                              "fill": "$foreground/foreground",
+                              "content": "Add sink",
+                              "fontFamily": "$typography/font-sans",
+                              "fontSize": 14,
+                              "fontWeight": "500"
+                            },
+                            {
+                              "type": "frame",
+                              "id": "SBeos",
+                              "name": "addSinkRow1",
+                              "width": "fill_container",
+                              "gap": 12,
+                              "children": [
+                                {
+                                  "id": "byGF9",
+                                  "type": "ref",
+                                  "ref": "aRqX6",
+                                  "name": "fieldSinkName",
+                                  "width": "fill_container",
+                                  "descendants": {
+                                    "ANxU1": {
+                                      "content": "Name"
+                                    },
+                                    "hokJ3": {
+                                      "content": "team-alerts",
+                                      "fill": "$foreground/foreground"
+                                    },
+                                    "OiyAM": {
+                                      "width": "fill_container"
+                                    },
+                                    "wolxN": {
+                                      "content": "A short lowercase identifier (letters, digits, and dashes) used to name the sink and its Secret — like team-alerts.",
+                                      "textGrowth": "fixed-width",
+                                      "width": "fill_container"
+                                    }
+                                  }
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "m1dk4",
+                                  "name": "fieldSinkKind",
+                                  "width": "fill_container",
+                                  "layout": "vertical",
+                                  "gap": 4,
+                                  "children": [
+                                    {
+                                      "type": "text",
+                                      "id": "mb3Yd",
+                                      "name": "fieldSinkKind Label",
+                                      "fill": "$foreground/foreground",
+                                      "content": "Kind",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 14,
+                                      "fontWeight": "500"
+                                    },
+                                    {
+                                      "id": "GLWbL",
+                                      "type": "ref",
+                                      "ref": "AT7ya",
+                                      "name": "fieldSinkKind Select",
+                                      "width": "fill_container",
+                                      "height": 40,
+                                      "descendants": {
+                                        "cFsFk": {
+                                          "content": "discord",
+                                          "fill": "$foreground/foreground"
+                                        }
+                                      }
+                                    }
+                                  ]
+                                }
+                              ]
+                            },
+                            {
+                              "type": "frame",
+                              "id": "PjvYr",
+                              "name": "addSinkRow2",
+                              "width": "fill_container",
+                              "gap": 12,
+                              "children": [
+                                {
+                                  "id": "bnTm0",
+                                  "type": "ref",
+                                  "ref": "aRqX6",
+                                  "name": "fieldSinkUrl",
+                                  "width": "fill_container",
+                                  "descendants": {
+                                    "ANxU1": {
+                                      "content": "Webhook URL"
+                                    },
+                                    "hokJ3": {
+                                      "content": "https://discord.com/api/webhooks/…",
+                                      "fill": "$field/placeholder"
+                                    },
+                                    "OiyAM": {
+                                      "enabled": false
+                                    }
+                                  }
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "ABfII",
+                                  "name": "fieldSinkLanguage",
+                                  "width": "fill_container",
+                                  "layout": "vertical",
+                                  "gap": 4,
+                                  "children": [
+                                    {
+                                      "type": "text",
+                                      "id": "UNBwv",
+                                      "name": "fieldSinkLanguage Label",
+                                      "fill": "$foreground/foreground",
+                                      "content": "Language",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 14,
+                                      "fontWeight": "500"
+                                    },
+                                    {
+                                      "id": "m12YV",
+                                      "type": "ref",
+                                      "ref": "AT7ya",
+                                      "name": "fieldSinkLanguage Select",
+                                      "width": "fill_container",
+                                      "height": 40,
+                                      "descendants": {
+                                        "cFsFk": {
+                                          "content": "Instance default",
+                                          "fill": "$foreground/foreground"
+                                        }
+                                      }
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "c8ZVI",
+                                      "name": "fieldSinkLanguage Hint Wrap",
+                                      "width": "fill_container",
+                                      "padding": [
+                                        0,
+                                        4
+                                      ],
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "tdGXR",
+                                          "name": "fieldSinkLanguage Hint",
+                                          "fill": "$muted",
+                                          "textGrowth": "fixed-width",
+                                          "width": "fill_container",
+                                          "content": "Notifications sent to this sink are written in this language.",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                }
+                              ]
+                            },
+                            {
+                              "type": "frame",
+                              "id": "E7eHV",
+                              "name": "addSinkEvents",
+                              "width": "fill_container",
+                              "layout": "vertical",
+                              "gap": 6,
+                              "children": [
+                                {
+                                  "type": "text",
+                                  "id": "Qc6AK",
+                                  "name": "addSinkEventsLabel",
+                                  "fill": "$muted",
+                                  "content": "Events (failures and recovery are pre-selected)",
+                                  "fontFamily": "$typography/font-sans",
+                                  "fontSize": 12,
+                                  "fontWeight": "normal"
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "mEY75",
+                                  "name": "addSinkEventRow",
+                                  "width": "fill_container",
+                                  "gap": 12,
+                                  "children": [
+                                    {
+                                      "type": "frame",
+                                      "id": "gG7HQ",
+                                      "name": "eventCell server.unhealthy",
+                                      "width": "fill_container",
+                                      "children": [
+                                        {
+                                          "id": "xWdJN",
+                                          "type": "ref",
+                                          "ref": "v6WNtR",
+                                          "name": "event server.unhealthy",
+                                          "descendants": {
+                                            "x7vJxB": {
+                                              "content": "server.unhealthy",
+                                              "fontFamily": "$typography/font-mono",
+                                              "fontSize": 12,
+                                              "fontWeight": "normal"
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "LAkyl",
+                                      "name": "eventCell server.recovered",
+                                      "width": "fill_container",
+                                      "children": [
+                                        {
+                                          "id": "sxrMR",
+                                          "type": "ref",
+                                          "ref": "v6WNtR",
+                                          "name": "event server.recovered",
+                                          "descendants": {
+                                            "x7vJxB": {
+                                              "content": "server.recovered",
+                                              "fontFamily": "$typography/font-mono",
+                                              "fontSize": 12,
+                                              "fontWeight": "normal"
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "hvIb3",
+                                  "name": "addSinkEventRow",
+                                  "width": "fill_container",
+                                  "gap": 12,
+                                  "children": [
+                                    {
+                                      "type": "frame",
+                                      "id": "lg04C",
+                                      "name": "eventCell backup.failed",
+                                      "width": "fill_container",
+                                      "children": [
+                                        {
+                                          "id": "Q0n3P2",
+                                          "type": "ref",
+                                          "ref": "v6WNtR",
+                                          "name": "event backup.failed",
+                                          "descendants": {
+                                            "x7vJxB": {
+                                              "content": "backup.failed",
+                                              "fontFamily": "$typography/font-mono",
+                                              "fontSize": 12,
+                                              "fontWeight": "normal"
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "plcUU",
+                                      "name": "eventCell backup.succeeded",
+                                      "width": "fill_container",
+                                      "children": [
+                                        {
+                                          "id": "oIWV7",
+                                          "type": "ref",
+                                          "ref": "aOvvm",
+                                          "name": "event backup.succeeded",
+                                          "descendants": {
+                                            "rKaQI": {
+                                              "content": "backup.succeeded",
+                                              "fontFamily": "$typography/font-mono",
+                                              "fontSize": 12,
+                                              "fontWeight": "normal"
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "dQGuO",
+                                  "name": "addSinkEventRow",
+                                  "width": "fill_container",
+                                  "gap": 12,
+                                  "children": [
+                                    {
+                                      "type": "frame",
+                                      "id": "mGHDE",
+                                      "name": "eventCell restore.failed",
+                                      "width": "fill_container",
+                                      "children": [
+                                        {
+                                          "id": "hKq8k",
+                                          "type": "ref",
+                                          "ref": "v6WNtR",
+                                          "name": "event restore.failed",
+                                          "descendants": {
+                                            "x7vJxB": {
+                                              "content": "restore.failed",
+                                              "fontFamily": "$typography/font-mono",
+                                              "fontSize": 12,
+                                              "fontWeight": "normal"
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "yMNPZ",
+                                      "name": "eventCell restore.succeeded",
+                                      "width": "fill_container",
+                                      "children": [
+                                        {
+                                          "id": "u73CU9",
+                                          "type": "ref",
+                                          "ref": "aOvvm",
+                                          "name": "event restore.succeeded",
+                                          "descendants": {
+                                            "rKaQI": {
+                                              "content": "restore.succeeded",
+                                              "fontFamily": "$typography/font-mono",
+                                              "fontSize": 12,
+                                              "fontWeight": "normal"
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                }
+                              ]
+                            },
+                            {
+                              "type": "frame",
+                              "id": "a1MTg",
+                              "name": "addSinkActions",
+                              "width": "fill_container",
+                              "gap": 8,
+                              "justifyContent": "end",
+                              "alignItems": "center",
+                              "children": [
+                                {
+                                  "id": "m63Yb",
+                                  "type": "ref",
+                                  "ref": "LMIom",
+                                  "name": "btnCancelAddSink",
+                                  "descendants": {
+                                    "vWtyO/bevQZ": {
+                                      "enabled": false
+                                    },
+                                    "vWtyO/ezEy1": {
+                                      "content": "Cancel"
+                                    }
+                                  }
+                                },
+                                {
+                                  "id": "lhyOq",
+                                  "type": "ref",
+                                  "ref": "tpKRk",
+                                  "name": "btnConfirmAddSink",
+                                  "descendants": {
+                                    "q58In/Xpn7K": {
+                                      "enabled": false
+                                    },
+                                    "q58In/U6q13B": {
+                                      "content": "Add sink"
+                                    }
+                                  }
+                                }
+                              ]
+                            }
+                          ]
+                        }
+                      ]
+                    },
+                    {
+                      "id": "P8FoV6",
+                      "type": "ref",
+                      "ref": "VvBaY",
+                      "name": "Card Actions",
+                      "width": "fill_container",
+                      "padding": [
+                        8,
+                        20,
+                        20,
+                        20
+                      ],
+                      "justifyContent": "end",
+                      "alignItems": "center",
+                      "children": [
+                        {
+                          "id": "dBGTB",
+                          "type": "ref",
+                          "ref": "tpKRk",
+                          "name": "Btn Save Changes",
+                          "descendants": {
+                            "q58In/Xpn7K": {
+                              "enabled": false
+                            },
+                            "q58In/U6q13B": {
+                              "content": "Save changes"
+                            }
+                          }
+                        }
+                      ]
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  ]
+}
diff --git a/assets/design-export/json/g2HLxz.json b/assets/design-export/json/g2HLxz.json
index 7e3822b33..a79c0a6a4 100644
--- a/assets/design-export/json/g2HLxz.json
+++ b/assets/design-export/json/g2HLxz.json
@@ -1 +1 @@
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diff --git a/assets/design-export/json/g5e2fM.json b/assets/design-export/json/g5e2fM.json
new file mode 100644
index 000000000..840741683
--- /dev/null
+++ b/assets/design-export/json/g5e2fM.json
@@ -0,0 +1,331 @@
+{
+  "type": "frame",
+  "id": "g5e2fM",
+  "x": 44960,
+  "y": -7988,
+  "name": "Screen/Mobile — Theme Settings · Language",
+  "theme": {
+    "semantic": "dark"
+  },
+  "clip": true,
+  "width": 390,
+  "height": 972,
+  "fill": "$background/background",
+  "layout": "vertical",
+  "children": [
+    {
+      "id": "DIxxO",
+      "type": "ref",
+      "ref": "fGbVF",
+      "name": "Mobile TopBar",
+      "width": "fill_container",
+      "descendants": {
+        "WOloN": {
+          "content": "Settings"
+        }
+      }
+    },
+    {
+      "type": "frame",
+      "id": "t91IL",
+      "name": "Body",
+      "width": "fill_container",
+      "fill": "$background/background",
+      "layout": "vertical",
+      "gap": 16,
+      "padding": 16,
+      "children": [
+        {
+          "id": "hArNp",
+          "type": "ref",
+          "ref": "xCDF7",
+          "name": "Page Header",
+          "width": "fill_container",
+          "descendants": {
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+              "width": "fill_container"
+            },
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+              "content": "Theme & Appearance",
+              "fontSize": 20
+            },
+            "VbHwU": {
+              "content": "Personal theme presets, colors, custom CSS, and theme portability.",
+              "textGrowth": "fixed-width",
+              "width": "fill_container"
+            },
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+              "enabled": false
+            }
+          }
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+          "type": "ref",
+          "ref": "Mp7Ep",
+          "name": "Settings Nav",
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+          "descendants": {
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+            "vbQ98": {
+              "fill": "$surface/secondary"
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+        {
+          "id": "us94F",
+          "type": "ref",
+          "ref": "XDZ0E",
+          "name": "Card Language",
+          "width": "fill_container",
+          "padding": 0,
+          "gap": 0,
+          "children": [
+            {
+              "id": "D7jwu",
+              "type": "ref",
+              "ref": "FRpsu",
+              "name": "Card Header",
+              "width": "fill_container",
+              "padding": [
+                20,
+                20,
+                16,
+                20
+              ],
+              "gap": 4,
+              "descendants": {
+                "fuZHB": {
+                  "content": "Language"
+                },
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+                  "textGrowth": "fixed-width",
+                  "width": "fill_container"
+                }
+              }
+            },
+            {
+              "type": "frame",
+              "id": "b6JE8K",
+              "name": "Card Fields",
+              "width": "fill_container",
+              "layout": "vertical",
+              "gap": 16,
+              "padding": [
+                0,
+                20,
+                20,
+                20
+              ],
+              "children": [
+                {
+                  "type": "frame",
+                  "id": "D40VEw",
+                  "name": "tsLangList",
+                  "width": "fill_container",
+                  "layout": "vertical",
+                  "gap": 8,
+                  "children": [
+                    {
+                      "type": "frame",
+                      "id": "F5hpA",
+                      "name": "tsLangAuto",
+                      "width": "fill_container",
+                      "fill": "$field/background",
+                      "cornerRadius": 10,
+                      "stroke": "$border/border",
+                      "strokeWidth": 1,
+                      "strokeAlignment": "inner",
+                      "gap": 12,
+                      "padding": [
+                        12,
+                        14
+                      ],
+                      "justifyContent": "space_between",
+                      "alignItems": "center",
+                      "children": [
+                        {
+                          "id": "WqJ9R",
+                          "type": "ref",
+                          "ref": "z2mDh",
+                          "name": "tsLangAuto Radio",
+                          "descendants": {
+                            "ocqPf": {
+                              "content": "Automatic (browser language)",
+                              "fontWeight": "500"
+                            }
+                          }
+                        }
+                      ]
+                    },
+                    {
+                      "type": "frame",
+                      "id": "Z7fgYZ",
+                      "name": "tsLangEn",
+                      "width": "fill_container",
+                      "fill": "$field/background",
+                      "cornerRadius": 10,
+                      "stroke": "$accent/accent",
+                      "strokeWidth": 1,
+                      "strokeAlignment": "inner",
+                      "gap": 12,
+                      "padding": [
+                        12,
+                        14
+                      ],
+                      "justifyContent": "space_between",
+                      "alignItems": "center",
+                      "children": [
+                        {
+                          "id": "eLGHw",
+                          "type": "ref",
+                          "ref": "T8ZnV",
+                          "name": "tsLangEn Radio",
+                          "descendants": {
+                            "jAx6p": {
+                              "content": "English",
+                              "fontWeight": "500"
+                            }
+                          }
+                        },
+                        {
+                          "type": "text",
+                          "id": "uXGYj",
+                          "name": "tsLangEn Completeness",
+                          "fill": "$muted",
+                          "content": "100% translated",
+                          "fontFamily": "$typography/font-sans",
+                          "fontSize": 12,
+                          "fontWeight": "normal"
+                        }
+                      ]
+                    },
+                    {
+                      "type": "frame",
+                      "id": "hwCIe",
+                      "name": "tsLangFr",
+                      "width": "fill_container",
+                      "fill": "$field/background",
+                      "cornerRadius": 10,
+                      "stroke": "$border/border",
+                      "strokeWidth": 1,
+                      "strokeAlignment": "inner",
+                      "gap": 12,
+                      "padding": [
+                        12,
+                        14
+                      ],
+                      "justifyContent": "space_between",
+                      "alignItems": "center",
+                      "children": [
+                        {
+                          "id": "qeTNN",
+                          "type": "ref",
+                          "ref": "z2mDh",
+                          "name": "tsLangFr Radio",
+                          "descendants": {
+                            "ocqPf": {
+                              "content": "Français",
+                              "fontWeight": "500"
+                            }
+                          }
+                        },
+                        {
+                          "type": "text",
+                          "id": "R01hG",
+                          "name": "tsLangFr Completeness",
+                          "fill": "$muted",
+                          "content": "100% translated",
+                          "fontFamily": "$typography/font-sans",
+                          "fontSize": 12,
+                          "fontWeight": "normal"
+                        }
+                      ]
+                    },
+                    {
+                      "type": "frame",
+                      "id": "BMrZn",
+                      "name": "tsLangDe",
+                      "width": "fill_container",
+                      "fill": "$field/background",
+                      "cornerRadius": 10,
+                      "stroke": "$border/border",
+                      "strokeWidth": 1,
+                      "strokeAlignment": "inner",
+                      "gap": 12,
+                      "padding": [
+                        12,
+                        14
+                      ],
+                      "justifyContent": "space_between",
+                      "alignItems": "center",
+                      "children": [
+                        {
+                          "id": "vxJJW",
+                          "type": "ref",
+                          "ref": "z2mDh",
+                          "name": "tsLangDe Radio",
+                          "descendants": {
+                            "ocqPf": {
+                              "content": "Deutsch",
+                              "fontWeight": "500"
+                            }
+                          }
+                        },
+                        {
+                          "type": "text",
+                          "id": "voh3P",
+                          "name": "tsLangDe Completeness",
+                          "fill": "$muted",
+                          "content": "86% translated",
+                          "fontFamily": "$typography/font-sans",
+                          "fontSize": 12,
+                          "fontWeight": "normal"
+                        }
+                      ]
+                    }
+                  ]
+                },
+                {
+                  "type": "frame",
+                  "id": "F5QWwF",
+                  "name": "tsLangNote",
+                  "width": "fill_container",
+                  "gap": 8,
+                  "alignItems": "center",
+                  "children": [
+                    {
+                      "type": "icon",
+                      "id": "P0J8GB",
+                      "name": "tsLangNoteIcon",
+                      "width": 14,
+                      "height": 14,
+                      "icon": "info",
+                      "library": "lucide",
+                      "fill": "$muted"
+                    },
+                    {
+                      "type": "text",
+                      "id": "pTutL",
+                      "name": "tsLangNoteText",
+                      "fill": "$muted",
+                      "textGrowth": "fixed-width",
+                      "width": "fill_container",
+                      "content": "Text that has not been translated yet is shown in English.",
+                      "fontFamily": "$typography/font-sans",
+                      "fontSize": 12,
+                      "fontWeight": "normal"
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  ]
+}
diff --git a/assets/design-export/json/gX7um.json b/assets/design-export/json/gX7um.json
index 3d63cacd8..3a49dbe06 100644
--- a/assets/design-export/json/gX7um.json
+++ b/assets/design-export/json/gX7um.json
@@ -1 +1 @@
-{"type":"frame","id":"gX7um","x":3280,"y":4500,"name":"Screen/Login (Light)","theme":{"semantic":"light"},"clip":true,"width":1440,"height":900,"fill":"$background/background","children":[{"id":"UQZOa","type":"ref","ref":"fjQjb","name":"loginL","width":"fill_container","height":"fill_container"},{"id":"YTPcQ","type":"ref","ref":"T8Hug","name":"loginR","width":"fill_container","height":"fill_container"}]}
+{"type":"frame","id":"gX7um","x":3280,"y":4500,"name":"Screen/Login (Light)","theme":{"semantic":"light"},"clip":true,"width":1440,"height":900,"fill":"$background/background","children":[{"id":"gsDFd","type":"ref","ref":"fjQjb","name":"loginL","width":"fill_container","height":"fill_container","children":[{"id":"Xsq1h","type":"ref","ref":"CDbjX","name":"loginCard"}]},{"id":"YTPcQ","type":"ref","ref":"T8Hug","name":"loginR","width":"fill_container","height":"fill_container"}]}
diff --git a/assets/design-export/json/lWvcv.json b/assets/design-export/json/lWvcv.json
index e9bc95e32..2e6bad270 100644
--- a/assets/design-export/json/lWvcv.json
+++ b/assets/design-export/json/lWvcv.json
@@ -9,7 +9,7 @@
   },
   "clip": true,
   "width": 1440,
-  "height": 2000,
+  "height": 2344,
   "fill": "$background/background",
   "children": [
     {
@@ -219,6 +219,257 @@
                   "layout": "vertical",
                   "gap": 16,
                   "children": [
+                    {
+                      "id": "FVPqf",
+                      "type": "ref",
+                      "ref": "XDZ0E",
+                      "name": "Card Language",
+                      "width": "fill_container",
+                      "padding": 0,
+                      "gap": 0,
+                      "children": [
+                        {
+                          "id": "E5N1t",
+                          "type": "ref",
+                          "ref": "FRpsu",
+                          "name": "Card Header",
+                          "width": "fill_container",
+                          "padding": [
+                            20,
+                            20,
+                            16,
+                            20
+                          ],
+                          "gap": 4,
+                          "descendants": {
+                            "fuZHB": {
+                              "content": "Language"
+                            },
+                            "BZG9o": {
+                              "content": "Choose the language of the dashboard. Your choice is saved to your account and follows you to every browser and device.",
+                              "textGrowth": "fixed-width",
+                              "width": "fill_container"
+                            }
+                          }
+                        },
+                        {
+                          "type": "frame",
+                          "id": "lVKGT",
+                          "name": "Card Fields",
+                          "width": "fill_container",
+                          "layout": "vertical",
+                          "gap": 16,
+                          "padding": [
+                            0,
+                            20,
+                            20,
+                            20
+                          ],
+                          "children": [
+                            {
+                              "type": "frame",
+                              "id": "KBpgk",
+                              "name": "tsLangList",
+                              "width": "fill_container",
+                              "layout": "vertical",
+                              "gap": 8,
+                              "children": [
+                                {
+                                  "type": "frame",
+                                  "id": "g2mRPb",
+                                  "name": "tsLangAuto",
+                                  "width": "fill_container",
+                                  "fill": "$field/background",
+                                  "cornerRadius": 10,
+                                  "stroke": "$border/border",
+                                  "strokeWidth": 1,
+                                  "strokeAlignment": "inner",
+                                  "gap": 12,
+                                  "padding": [
+                                    12,
+                                    14
+                                  ],
+                                  "justifyContent": "space_between",
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "id": "rbSF2",
+                                      "type": "ref",
+                                      "ref": "z2mDh",
+                                      "name": "tsLangAuto Radio",
+                                      "descendants": {
+                                        "ocqPf": {
+                                          "content": "Automatic (browser language)",
+                                          "fontWeight": "500"
+                                        }
+                                      }
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "rwNZQ",
+                                  "name": "tsLangEn",
+                                  "width": "fill_container",
+                                  "fill": "$field/background",
+                                  "cornerRadius": 10,
+                                  "stroke": "$accent/accent",
+                                  "strokeWidth": 1,
+                                  "strokeAlignment": "inner",
+                                  "gap": 12,
+                                  "padding": [
+                                    12,
+                                    14
+                                  ],
+                                  "justifyContent": "space_between",
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "id": "e5R4W",
+                                      "type": "ref",
+                                      "ref": "T8ZnV",
+                                      "name": "tsLangEn Radio",
+                                      "descendants": {
+                                        "jAx6p": {
+                                          "content": "English",
+                                          "fontWeight": "500"
+                                        }
+                                      }
+                                    },
+                                    {
+                                      "type": "text",
+                                      "id": "gdYrd",
+                                      "name": "tsLangEn Completeness",
+                                      "fill": "$muted",
+                                      "content": "100% translated",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 12,
+                                      "fontWeight": "normal"
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "XxjWX",
+                                  "name": "tsLangFr",
+                                  "width": "fill_container",
+                                  "fill": "$field/background",
+                                  "cornerRadius": 10,
+                                  "stroke": "$border/border",
+                                  "strokeWidth": 1,
+                                  "strokeAlignment": "inner",
+                                  "gap": 12,
+                                  "padding": [
+                                    12,
+                                    14
+                                  ],
+                                  "justifyContent": "space_between",
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "id": "MU5SM",
+                                      "type": "ref",
+                                      "ref": "z2mDh",
+                                      "name": "tsLangFr Radio",
+                                      "descendants": {
+                                        "ocqPf": {
+                                          "content": "Français",
+                                          "fontWeight": "500"
+                                        }
+                                      }
+                                    },
+                                    {
+                                      "type": "text",
+                                      "id": "Xeuio",
+                                      "name": "tsLangFr Completeness",
+                                      "fill": "$muted",
+                                      "content": "100% translated",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 12,
+                                      "fontWeight": "normal"
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "Ip3AK",
+                                  "name": "tsLangDe",
+                                  "width": "fill_container",
+                                  "fill": "$field/background",
+                                  "cornerRadius": 10,
+                                  "stroke": "$border/border",
+                                  "strokeWidth": 1,
+                                  "strokeAlignment": "inner",
+                                  "gap": 12,
+                                  "padding": [
+                                    12,
+                                    14
+                                  ],
+                                  "justifyContent": "space_between",
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "id": "VlbLF",
+                                      "type": "ref",
+                                      "ref": "z2mDh",
+                                      "name": "tsLangDe Radio",
+                                      "descendants": {
+                                        "ocqPf": {
+                                          "content": "Deutsch",
+                                          "fontWeight": "500"
+                                        }
+                                      }
+                                    },
+                                    {
+                                      "type": "text",
+                                      "id": "dl77o",
+                                      "name": "tsLangDe Completeness",
+                                      "fill": "$muted",
+                                      "content": "86% translated",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 12,
+                                      "fontWeight": "normal"
+                                    }
+                                  ]
+                                }
+                              ]
+                            },
+                            {
+                              "type": "frame",
+                              "id": "jQ1Jm",
+                              "name": "tsLangNote",
+                              "width": "fill_container",
+                              "gap": 8,
+                              "alignItems": "center",
+                              "children": [
+                                {
+                                  "type": "icon",
+                                  "id": "l5IVh",
+                                  "name": "tsLangNoteIcon",
+                                  "width": 14,
+                                  "height": 14,
+                                  "icon": "info",
+                                  "library": "lucide",
+                                  "fill": "$muted"
+                                },
+                                {
+                                  "type": "text",
+                                  "id": "qaRbL",
+                                  "name": "tsLangNoteText",
+                                  "fill": "$muted",
+                                  "textGrowth": "fixed-width",
+                                  "width": "fill_container",
+                                  "content": "Text that has not been translated yet is shown in English.",
+                                  "fontFamily": "$typography/font-sans",
+                                  "fontSize": 12,
+                                  "fontWeight": "normal"
+                                }
+                              ]
+                            }
+                          ]
+                        }
+                      ]
+                    },
                     {
                       "id": "T6d1Wb",
                       "type": "ref",
diff --git a/assets/design-export/json/ljdA5.json b/assets/design-export/json/ljdA5.json
index 9072e6343..4d86e8749 100644
--- a/assets/design-export/json/ljdA5.json
+++ b/assets/design-export/json/ljdA5.json
@@ -171,6 +171,29 @@
               "fontFamily": "$typography/font-sans",
               "fontSize": 11,
               "fontWeight": "normal"
+            },
+            {
+              "type": "frame",
+              "id": "uwvzA",
+              "layoutPosition": "absolute",
+              "x": 0,
+              "y": 12,
+              "name": "loginLangRow",
+              "width": 420,
+              "padding": [
+                0,
+                12
+              ],
+              "justifyContent": "end",
+              "alignItems": "center",
+              "children": [
+                {
+                  "id": "fMy1s",
+                  "type": "ref",
+                  "ref": "Jf27F",
+                  "name": "langPicker"
+                }
+              ]
             }
           ]
         }
diff --git a/assets/design-export/json/n6Xlo.json b/assets/design-export/json/n6Xlo.json
index c775271f2..98dd73e16 100644
--- a/assets/design-export/json/n6Xlo.json
+++ b/assets/design-export/json/n6Xlo.json
@@ -223,6 +223,50 @@
                                       "fontFamily": "$typography/font-sans",
                                       "fontSize": 12,
                                       "fontWeight": "normal"
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "DTGe6",
+                                      "name": "sinkLangRow",
+                                      "gap": 8,
+                                      "padding": [
+                                        6,
+                                        0,
+                                        0,
+                                        0
+                                      ],
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "axNVI",
+                                          "name": "sinkLangLabel",
+                                          "fill": "$muted",
+                                          "content": "Language",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        },
+                                        {
+                                          "id": "B4seX",
+                                          "type": "ref",
+                                          "ref": "AT7ya",
+                                          "name": "sinkLangSelect",
+                                          "width": 200,
+                                          "height": 32,
+                                          "padding": [
+                                            6,
+                                            10
+                                          ],
+                                          "descendants": {
+                                            "cFsFk": {
+                                              "content": "Français",
+                                              "fill": "$foreground/foreground",
+                                              "fontSize": 13
+                                            }
+                                          }
+                                        }
+                                      ]
                                     }
                                   ]
                                 },
@@ -395,6 +439,50 @@
                                       "fontFamily": "$typography/font-sans",
                                       "fontSize": 12,
                                       "fontWeight": "normal"
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "TEVSf",
+                                      "name": "sinkLangRow",
+                                      "gap": 8,
+                                      "padding": [
+                                        6,
+                                        0,
+                                        0,
+                                        0
+                                      ],
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "NiCQX",
+                                          "name": "sinkLangLabel",
+                                          "fill": "$muted",
+                                          "content": "Language",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        },
+                                        {
+                                          "id": "NCMJz",
+                                          "type": "ref",
+                                          "ref": "AT7ya",
+                                          "name": "sinkLangSelect",
+                                          "width": 200,
+                                          "height": 32,
+                                          "padding": [
+                                            6,
+                                            10
+                                          ],
+                                          "descendants": {
+                                            "cFsFk": {
+                                              "content": "Instance default",
+                                              "fill": "$foreground/foreground",
+                                              "fontSize": 13
+                                            }
+                                          }
+                                        }
+                                      ]
                                     }
                                   ]
                                 },
diff --git a/assets/design-export/screenshots/C2LQE4.png b/assets/design-export/screenshots/C2LQE4.png
index 5f58ff38e..be5fbaf4f 100644
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diff --git a/assets/design-export/screenshots/CDbjX.png b/assets/design-export/screenshots/CDbjX.png
new file mode 100644
index 000000000..4f8bf2626
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diff --git a/assets/design-export/screenshots/EcoGD.png b/assets/design-export/screenshots/EcoGD.png
index 90145292b..ea4439b0a 100644
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diff --git a/assets/design-export/screenshots/FBiMN.png b/assets/design-export/screenshots/FBiMN.png
index d7f72c406..0f65a9642 100644
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index 000000000..486ad9234
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diff --git a/assets/design-export/screenshots/HKEl2.png b/assets/design-export/screenshots/HKEl2.png
index ac2ce2ea1..e1eea0d46 100644
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diff --git a/assets/design-export/screenshots/Jf27F.png b/assets/design-export/screenshots/Jf27F.png
new file mode 100644
index 000000000..4efc0458e
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diff --git a/assets/design-export/screenshots/N1GkB.png b/assets/design-export/screenshots/N1GkB.png
index 60fb6e146..1cdc28bd9 100644
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diff --git a/assets/design-export/screenshots/T1wkiT.png b/assets/design-export/screenshots/T1wkiT.png
index fd784ebc0..dacc8bae1 100644
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diff --git a/assets/design-export/screenshots/WZdnw.png b/assets/design-export/screenshots/WZdnw.png
index 813d114df..9475b2c50 100644
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index 000000000..5259539bb
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diff --git a/assets/design-export/screenshots/epZO2.png b/assets/design-export/screenshots/epZO2.png
index 9c906b40c..ca83b98c6 100644
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index 2ef456f83..b98f1bd65 100644
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diff --git a/assets/design-export/screenshots/g5e2fM.png b/assets/design-export/screenshots/g5e2fM.png
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index 000000000..e1c68e6bd
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diff --git a/assets/design-export/screenshots/gX7um.png b/assets/design-export/screenshots/gX7um.png
index fa71a8715..8c19ed5ad 100644
Binary files a/assets/design-export/screenshots/gX7um.png and b/assets/design-export/screenshots/gX7um.png differ
diff --git a/assets/design-export/screenshots/jmoi3.png b/assets/design-export/screenshots/jmoi3.png
index 2c858a3d3..1dcfdd674 100644
Binary files a/assets/design-export/screenshots/jmoi3.png and b/assets/design-export/screenshots/jmoi3.png differ
diff --git a/assets/design-export/screenshots/lWvcv.png b/assets/design-export/screenshots/lWvcv.png
index 90f78d4c1..8f4017882 100644
Binary files a/assets/design-export/screenshots/lWvcv.png and b/assets/design-export/screenshots/lWvcv.png differ
diff --git a/assets/design-export/screenshots/ljdA5.png b/assets/design-export/screenshots/ljdA5.png
index 81d3d29c7..4ed4c570b 100644
Binary files a/assets/design-export/screenshots/ljdA5.png and b/assets/design-export/screenshots/ljdA5.png differ
diff --git a/assets/design-export/screenshots/n6Xlo.png b/assets/design-export/screenshots/n6Xlo.png
index f6474697b..90a4bca48 100644
Binary files a/assets/design-export/screenshots/n6Xlo.png and b/assets/design-export/screenshots/n6Xlo.png differ
diff --git a/assets/design-export/screenshots/q31B6w.png b/assets/design-export/screenshots/q31B6w.png
index d6268944e..feb85bb9e 100644
Binary files a/assets/design-export/screenshots/q31B6w.png and b/assets/design-export/screenshots/q31B6w.png differ
diff --git a/assets/design-export/screenshots/qFLfB.png b/assets/design-export/screenshots/qFLfB.png
index 0f941b2c1..22350088b 100644
Binary files a/assets/design-export/screenshots/qFLfB.png and b/assets/design-export/screenshots/qFLfB.png differ
diff --git a/charts/gameplane/crd-manifests/gameplane.local_backups.yaml b/charts/gameplane/crd-manifests/gameplane.local_backups.yaml
index eff85794e..d902ea995 100644
--- a/charts/gameplane/crd-manifests/gameplane.local_backups.yaml
+++ b/charts/gameplane/crd-manifests/gameplane.local_backups.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: backups.gameplane.local
 spec:
diff --git a/charts/gameplane/crd-manifests/gameplane.local_backupschedules.yaml b/charts/gameplane/crd-manifests/gameplane.local_backupschedules.yaml
index f0695a89a..d85406090 100644
--- a/charts/gameplane/crd-manifests/gameplane.local_backupschedules.yaml
+++ b/charts/gameplane/crd-manifests/gameplane.local_backupschedules.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: backupschedules.gameplane.local
 spec:
diff --git a/charts/gameplane/crd-manifests/gameplane.local_clusters.yaml b/charts/gameplane/crd-manifests/gameplane.local_clusters.yaml
index 511882770..4d6aadcbb 100644
--- a/charts/gameplane/crd-manifests/gameplane.local_clusters.yaml
+++ b/charts/gameplane/crd-manifests/gameplane.local_clusters.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: clusters.gameplane.local
 spec:
diff --git a/charts/gameplane/crd-manifests/gameplane.local_gameservers.yaml b/charts/gameplane/crd-manifests/gameplane.local_gameservers.yaml
index bf736e402..95178e56e 100644
--- a/charts/gameplane/crd-manifests/gameplane.local_gameservers.yaml
+++ b/charts/gameplane/crd-manifests/gameplane.local_gameservers.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: gameservers.gameplane.local
 spec:
@@ -2442,6 +2442,20 @@ spec:
                     format: int32
                     type: integer
                 type: object
+              conditionArgs:
+                additionalProperties:
+                  additionalProperties:
+                    type: string
+                  type: object
+                description: |-
+                  ConditionArgs carries, per condition Type, the values interpolated into
+                  that condition's English message, so clients can render the localized
+                  message for the condition's current Reason (translation id
+                  condition.<type>.<reason>, lower-cased). The English Message is
+                  unchanged and stays the fallback. An entry exists only while the
+                  condition's current Reason has arguments; it is removed when the Reason
+                  changes to one without.
+                type: object
               conditions:
                 description: |-
                   Conditions carry detailed state transitions. Standard Ready,
diff --git a/charts/gameplane/crd-manifests/gameplane.local_gametemplates.yaml b/charts/gameplane/crd-manifests/gameplane.local_gametemplates.yaml
index 085756fe1..e5e3e1e3b 100644
--- a/charts/gameplane/crd-manifests/gameplane.local_gametemplates.yaml
+++ b/charts/gameplane/crd-manifests/gameplane.local_gametemplates.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: gametemplates.gameplane.local
 spec:
@@ -2477,6 +2477,65 @@ spec:
               static configuration. The operator populates ObservedGeneration so
               controllers reading templates can detect spec updates.
             properties:
+              conditions:
+                description: |-
+                  Conditions carry detailed state. LocalesValid reports whether the
+                  translations shipped with the module bundle were all valid.
+                items:
+                  description: Condition contains details for one aspect of the current
+                    state of this API Resource.
+                  properties:
+                    lastTransitionTime:
+                      description: |-
+                        lastTransitionTime is the last time the condition transitioned from one status to another.
+                        This should be when the underlying condition changed.  If that is not known, then using the time when the API field changed is acceptable.
+                      format: date-time
+                      type: string
+                    message:
+                      description: |-
+                        message is a human readable message indicating details about the transition.
+                        This may be an empty string.
+                      maxLength: 32768
+                      type: string
+                    observedGeneration:
+                      description: |-
+                        observedGeneration represents the .metadata.generation that the condition was set based upon.
+                        For instance, if .metadata.generation is currently 12, but the .status.conditions[x].observedGeneration is 9, the condition is out of date
+                        with respect to the current state of the instance.
+                      format: int64
+                      minimum: 0
+                      type: integer
+                    reason:
+                      description: |-
+                        reason contains a programmatic identifier indicating the reason for the condition's last transition.
+                        Producers of specific condition types may define expected values and meanings for this field,
+                        and whether the values are considered a guaranteed API.
+                        The value should be a CamelCase string.
+                        This field may not be empty.
+                      maxLength: 1024
+                      minLength: 1
+                      pattern: ^[A-Za-z]([A-Za-z0-9_,:]*[A-Za-z0-9_])?$
+                      type: string
+                    status:
+                      description: status of the condition, one of True, False, Unknown.
+                      enum:
+                      - "True"
+                      - "False"
+                      - Unknown
+                      type: string
+                    type:
+                      description: type of condition in CamelCase or in foo.example.com/CamelCase.
+                      maxLength: 316
+                      pattern: ^([a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*/)?(([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9])$
+                      type: string
+                  required:
+                  - lastTransitionTime
+                  - message
+                  - reason
+                  - status
+                  - type
+                  type: object
+                type: array
               inUseCount:
                 description: |-
                   InUseCount is the number of GameServers currently referencing
diff --git a/charts/gameplane/crd-manifests/gameplane.local_modules.yaml b/charts/gameplane/crd-manifests/gameplane.local_modules.yaml
index 4a940499a..5ade28cee 100644
--- a/charts/gameplane/crd-manifests/gameplane.local_modules.yaml
+++ b/charts/gameplane/crd-manifests/gameplane.local_modules.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: modules.gameplane.local
 spec:
diff --git a/charts/gameplane/crd-manifests/gameplane.local_modulesources.yaml b/charts/gameplane/crd-manifests/gameplane.local_modulesources.yaml
index f5aceda0a..6c5dcbf36 100644
--- a/charts/gameplane/crd-manifests/gameplane.local_modulesources.yaml
+++ b/charts/gameplane/crd-manifests/gameplane.local_modulesources.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: modulesources.gameplane.local
 spec:
diff --git a/charts/gameplane/crd-manifests/gameplane.local_networkcaptures.yaml b/charts/gameplane/crd-manifests/gameplane.local_networkcaptures.yaml
index b8ce9f11f..cc113e7e8 100644
--- a/charts/gameplane/crd-manifests/gameplane.local_networkcaptures.yaml
+++ b/charts/gameplane/crd-manifests/gameplane.local_networkcaptures.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: networkcaptures.gameplane.local
 spec:
diff --git a/charts/gameplane/crd-manifests/gameplane.local_restores.yaml b/charts/gameplane/crd-manifests/gameplane.local_restores.yaml
index d00529d8b..b77cd5c25 100644
--- a/charts/gameplane/crd-manifests/gameplane.local_restores.yaml
+++ b/charts/gameplane/crd-manifests/gameplane.local_restores.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: restores.gameplane.local
 spec:
diff --git a/charts/gameplane/crds/gameplane.local_backups.yaml b/charts/gameplane/crds/gameplane.local_backups.yaml
index eff85794e..d902ea995 100644
--- a/charts/gameplane/crds/gameplane.local_backups.yaml
+++ b/charts/gameplane/crds/gameplane.local_backups.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: backups.gameplane.local
 spec:
diff --git a/charts/gameplane/crds/gameplane.local_backupschedules.yaml b/charts/gameplane/crds/gameplane.local_backupschedules.yaml
index f0695a89a..d85406090 100644
--- a/charts/gameplane/crds/gameplane.local_backupschedules.yaml
+++ b/charts/gameplane/crds/gameplane.local_backupschedules.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: backupschedules.gameplane.local
 spec:
diff --git a/charts/gameplane/crds/gameplane.local_clusters.yaml b/charts/gameplane/crds/gameplane.local_clusters.yaml
index 511882770..4d6aadcbb 100644
--- a/charts/gameplane/crds/gameplane.local_clusters.yaml
+++ b/charts/gameplane/crds/gameplane.local_clusters.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: clusters.gameplane.local
 spec:
diff --git a/charts/gameplane/crds/gameplane.local_gameservers.yaml b/charts/gameplane/crds/gameplane.local_gameservers.yaml
index bf736e402..95178e56e 100644
--- a/charts/gameplane/crds/gameplane.local_gameservers.yaml
+++ b/charts/gameplane/crds/gameplane.local_gameservers.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: gameservers.gameplane.local
 spec:
@@ -2442,6 +2442,20 @@ spec:
                     format: int32
                     type: integer
                 type: object
+              conditionArgs:
+                additionalProperties:
+                  additionalProperties:
+                    type: string
+                  type: object
+                description: |-
+                  ConditionArgs carries, per condition Type, the values interpolated into
+                  that condition's English message, so clients can render the localized
+                  message for the condition's current Reason (translation id
+                  condition.<type>.<reason>, lower-cased). The English Message is
+                  unchanged and stays the fallback. An entry exists only while the
+                  condition's current Reason has arguments; it is removed when the Reason
+                  changes to one without.
+                type: object
               conditions:
                 description: |-
                   Conditions carry detailed state transitions. Standard Ready,
diff --git a/charts/gameplane/crds/gameplane.local_gametemplates.yaml b/charts/gameplane/crds/gameplane.local_gametemplates.yaml
index 085756fe1..e5e3e1e3b 100644
--- a/charts/gameplane/crds/gameplane.local_gametemplates.yaml
+++ b/charts/gameplane/crds/gameplane.local_gametemplates.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: gametemplates.gameplane.local
 spec:
@@ -2477,6 +2477,65 @@ spec:
               static configuration. The operator populates ObservedGeneration so
               controllers reading templates can detect spec updates.
             properties:
+              conditions:
+                description: |-
+                  Conditions carry detailed state. LocalesValid reports whether the
+                  translations shipped with the module bundle were all valid.
+                items:
+                  description: Condition contains details for one aspect of the current
+                    state of this API Resource.
+                  properties:
+                    lastTransitionTime:
+                      description: |-
+                        lastTransitionTime is the last time the condition transitioned from one status to another.
+                        This should be when the underlying condition changed.  If that is not known, then using the time when the API field changed is acceptable.
+                      format: date-time
+                      type: string
+                    message:
+                      description: |-
+                        message is a human readable message indicating details about the transition.
+                        This may be an empty string.
+                      maxLength: 32768
+                      type: string
+                    observedGeneration:
+                      description: |-
+                        observedGeneration represents the .metadata.generation that the condition was set based upon.
+                        For instance, if .metadata.generation is currently 12, but the .status.conditions[x].observedGeneration is 9, the condition is out of date
+                        with respect to the current state of the instance.
+                      format: int64
+                      minimum: 0
+                      type: integer
+                    reason:
+                      description: |-
+                        reason contains a programmatic identifier indicating the reason for the condition's last transition.
+                        Producers of specific condition types may define expected values and meanings for this field,
+                        and whether the values are considered a guaranteed API.
+                        The value should be a CamelCase string.
+                        This field may not be empty.
+                      maxLength: 1024
+                      minLength: 1
+                      pattern: ^[A-Za-z]([A-Za-z0-9_,:]*[A-Za-z0-9_])?$
+                      type: string
+                    status:
+                      description: status of the condition, one of True, False, Unknown.
+                      enum:
+                      - "True"
+                      - "False"
+                      - Unknown
+                      type: string
+                    type:
+                      description: type of condition in CamelCase or in foo.example.com/CamelCase.
+                      maxLength: 316
+                      pattern: ^([a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*/)?(([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9])$
+                      type: string
+                  required:
+                  - lastTransitionTime
+                  - message
+                  - reason
+                  - status
+                  - type
+                  type: object
+                type: array
               inUseCount:
                 description: |-
                   InUseCount is the number of GameServers currently referencing
diff --git a/charts/gameplane/crds/gameplane.local_modules.yaml b/charts/gameplane/crds/gameplane.local_modules.yaml
index 4a940499a..5ade28cee 100644
--- a/charts/gameplane/crds/gameplane.local_modules.yaml
+++ b/charts/gameplane/crds/gameplane.local_modules.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: modules.gameplane.local
 spec:
diff --git a/charts/gameplane/crds/gameplane.local_modulesources.yaml b/charts/gameplane/crds/gameplane.local_modulesources.yaml
index f5aceda0a..6c5dcbf36 100644
--- a/charts/gameplane/crds/gameplane.local_modulesources.yaml
+++ b/charts/gameplane/crds/gameplane.local_modulesources.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: modulesources.gameplane.local
 spec:
diff --git a/charts/gameplane/crds/gameplane.local_networkcaptures.yaml b/charts/gameplane/crds/gameplane.local_networkcaptures.yaml
index b8ce9f11f..cc113e7e8 100644
--- a/charts/gameplane/crds/gameplane.local_networkcaptures.yaml
+++ b/charts/gameplane/crds/gameplane.local_networkcaptures.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: networkcaptures.gameplane.local
 spec:
diff --git a/charts/gameplane/crds/gameplane.local_restores.yaml b/charts/gameplane/crds/gameplane.local_restores.yaml
index d00529d8b..b77cd5c25 100644
--- a/charts/gameplane/crds/gameplane.local_restores.yaml
+++ b/charts/gameplane/crds/gameplane.local_restores.yaml
@@ -3,7 +3,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    gameplane.local/crd-bundle-sha256: d5069bc379d1aee86475b0f63c6c2866423a381b14b44cbf7a77dfd63e3c1c6a
+    gameplane.local/crd-bundle-sha256: 181aeee1d52a9cb178b0f8a8a862dc5959e772facf11817d5e70e5196574cd4c
     controller-gen.kubebuilder.io/version: v0.20.1
   name: restores.gameplane.local
 spec:
diff --git a/design.pen b/design.pen
index 33c7e7d41..761d42047 100644
--- a/design.pen
+++ b/design.pen
@@ -16,12 +16,20 @@
       "fill": "$background/background",
       "children": [
         {
-          "id": "sUdzl",
+          "id": "TbEIq",
           "type": "ref",
           "ref": "fjQjb",
           "name": "loginL",
           "width": "fill_container",
-          "height": "fill_container"
+          "height": "fill_container",
+          "children": [
+            {
+              "id": "KTRiy",
+              "type": "ref",
+              "ref": "CDbjX",
+              "name": "loginCard"
+            }
+          ]
         },
         {
           "id": "X7z8B",
@@ -246,6 +254,29 @@
                   "fontFamily": "$typography/font-sans",
                   "fontSize": 11,
                   "fontWeight": "normal"
+                },
+                {
+                  "type": "frame",
+                  "id": "uwvzA",
+                  "layoutPosition": "absolute",
+                  "x": 0,
+                  "y": 12,
+                  "name": "loginLangRow",
+                  "width": 420,
+                  "padding": [
+                    0,
+                    12
+                  ],
+                  "justifyContent": "end",
+                  "alignItems": "center",
+                  "children": [
+                    {
+                      "id": "fMy1s",
+                      "type": "ref",
+                      "ref": "Jf27F",
+                      "name": "langPicker"
+                    }
+                  ]
                 }
               ]
             }
@@ -32260,127 +32291,166 @@
                       "width": 220
                     },
                     {
-                      "id": "l4Iw3z",
-                      "type": "ref",
-                      "ref": "XDZ0E",
-                      "name": "Settings Panel",
+                      "type": "frame",
+                      "id": "v38YR",
+                      "name": "Panel Column",
                       "width": "fill_container",
-                      "padding": 0,
-                      "gap": 0,
+                      "layout": "vertical",
+                      "gap": 24,
                       "children": [
                         {
-                          "id": "tXDnN",
+                          "id": "l4Iw3z",
                           "type": "ref",
-                          "ref": "FRpsu",
-                          "name": "Card Header",
-                          "width": "fill_container",
-                          "padding": [
-                            20,
-                            20,
-                            16,
-                            20
-                          ],
-                          "gap": 4,
-                          "descendants": {
-                            "fuZHB": {
-                              "content": "General"
-                            },
-                            "BZG9o": {
-                              "content": "Basic identity for this Gameplane instance."
-                            }
-                          }
-                        },
-                        {
-                          "type": "frame",
-                          "id": "DI9X5",
-                          "name": "Card Fields",
+                          "ref": "XDZ0E",
+                          "name": "Settings Panel",
                           "width": "fill_container",
-                          "layout": "vertical",
-                          "gap": 16,
-                          "padding": [
-                            0,
-                            20
-                          ],
+                          "padding": 0,
+                          "gap": 0,
                           "children": [
                             {
-                              "type": "frame",
-                              "id": "BGqdF",
-                              "name": "fieldInstanceName",
+                              "id": "tXDnN",
+                              "type": "ref",
+                              "ref": "FRpsu",
+                              "name": "Card Header",
                               "width": "fill_container",
-                              "layout": "vertical",
-                              "children": [
-                                {
-                                  "id": "E8BwC",
-                                  "type": "ref",
-                                  "ref": "aRqX6",
-                                  "name": "Input/Primary",
-                                  "width": "fill_container",
-                                  "descendants": {
-                                    "ANxU1": {
-                                      "content": "Instance name"
-                                    },
-                                    "hokJ3": {
-                                      "content": "",
-                                      "fill": "$field/placeholder"
-                                    },
-                                    "wolxN": {
-                                      "content": "Optional. Names this install on the Cluster page and in notifications."
-                                    }
-                                  }
+                              "padding": [
+                                20,
+                                20,
+                                16,
+                                20
+                              ],
+                              "gap": 4,
+                              "descendants": {
+                                "fuZHB": {
+                                  "content": "General"
+                                },
+                                "BZG9o": {
+                                  "content": "Basic identity for this Gameplane instance."
                                 }
-                              ]
+                              }
                             },
                             {
                               "type": "frame",
-                              "id": "yjujL",
-                              "name": "fieldExternalURL",
+                              "id": "DI9X5",
+                              "name": "Card Fields",
                               "width": "fill_container",
                               "layout": "vertical",
+                              "gap": 16,
+                              "padding": [
+                                0,
+                                20
+                              ],
                               "children": [
                                 {
-                                  "id": "YesmO",
-                                  "type": "ref",
-                                  "ref": "aRqX6",
-                                  "name": "Input/Primary",
+                                  "type": "frame",
+                                  "id": "BGqdF",
+                                  "name": "fieldInstanceName",
                                   "width": "fill_container",
-                                  "descendants": {
-                                    "ANxU1": {
-                                      "content": "External URL"
-                                    },
-                                    "hokJ3": {
-                                      "content": "",
-                                      "fill": "$field/placeholder"
-                                    },
-                                    "wolxN": {
-                                      "content": "Canonical base URL, used in emails, webhooks, OIDC callbacks."
+                                  "layout": "vertical",
+                                  "children": [
+                                    {
+                                      "id": "E8BwC",
+                                      "type": "ref",
+                                      "ref": "aRqX6",
+                                      "name": "Input/Primary",
+                                      "width": "fill_container",
+                                      "descendants": {
+                                        "ANxU1": {
+                                          "content": "Instance name"
+                                        },
+                                        "hokJ3": {
+                                          "content": "",
+                                          "fill": "$field/placeholder"
+                                        },
+                                        "wolxN": {
+                                          "content": "Optional. Names this install on the Cluster page and in notifications."
+                                        }
+                                      }
                                     }
-                                  }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "yjujL",
+                                  "name": "fieldExternalURL",
+                                  "width": "fill_container",
+                                  "layout": "vertical",
+                                  "children": [
+                                    {
+                                      "id": "YesmO",
+                                      "type": "ref",
+                                      "ref": "aRqX6",
+                                      "name": "Input/Primary",
+                                      "width": "fill_container",
+                                      "descendants": {
+                                        "ANxU1": {
+                                          "content": "External URL"
+                                        },
+                                        "hokJ3": {
+                                          "content": "",
+                                          "fill": "$field/placeholder"
+                                        },
+                                        "wolxN": {
+                                          "content": "Canonical base URL, used in emails, webhooks, OIDC callbacks."
+                                        }
+                                      }
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "l6wE1E",
+                                  "name": "fieldDefaultNamespace",
+                                  "width": "fill_container",
+                                  "layout": "vertical",
+                                  "children": [
+                                    {
+                                      "id": "SVLor",
+                                      "type": "ref",
+                                      "ref": "aRqX6",
+                                      "name": "Input/Primary",
+                                      "width": "fill_container",
+                                      "descendants": {
+                                        "ANxU1": {
+                                          "content": "Default namespace"
+                                        },
+                                        "hokJ3": {
+                                          "content": "gameplane-games",
+                                          "fill": "$foreground/foreground"
+                                        },
+                                        "wolxN": {
+                                          "content": "Where new GameServers land by default."
+                                        }
+                                      }
+                                    }
+                                  ]
                                 }
                               ]
                             },
                             {
                               "type": "frame",
-                              "id": "l6wE1E",
-                              "name": "fieldDefaultNamespace",
+                              "id": "Aey03",
+                              "name": "Card Actions",
                               "width": "fill_container",
-                              "layout": "vertical",
+                              "padding": [
+                                8,
+                                20,
+                                20,
+                                20
+                              ],
+                              "justifyContent": "end",
                               "children": [
                                 {
-                                  "id": "SVLor",
+                                  "id": "KmwSz",
                                   "type": "ref",
-                                  "ref": "aRqX6",
-                                  "name": "Input/Primary",
-                                  "width": "fill_container",
+                                  "ref": "tpKRk",
+                                  "name": "Btn Save Changes",
                                   "descendants": {
-                                    "ANxU1": {
-                                      "content": "Default namespace"
-                                    },
-                                    "hokJ3": {
-                                      "content": "gameplane-games",
-                                      "fill": "$foreground/foreground"
+                                    "q58In/Xpn7K": {
+                                      "enabled": false
                                     },
-                                    "wolxN": {
-                                      "content": "Where new GameServers land by default."
+                                    "q58In/U6q13B": {
+                                      "content": "Save changes"
                                     }
                                   }
                                 }
@@ -32389,31 +32459,138 @@
                           ]
                         },
                         {
-                          "type": "frame",
-                          "id": "Aey03",
-                          "name": "Card Actions",
+                          "id": "noNHt",
+                          "type": "ref",
+                          "ref": "XDZ0E",
+                          "name": "Language Panel",
                           "width": "fill_container",
-                          "padding": [
-                            8,
-                            20,
-                            20,
-                            20
-                          ],
-                          "justifyContent": "end",
+                          "padding": 0,
+                          "gap": 0,
                           "children": [
                             {
-                              "id": "KmwSz",
+                              "id": "F1k5Xe",
                               "type": "ref",
-                              "ref": "tpKRk",
-                              "name": "Btn Save Changes",
+                              "ref": "FRpsu",
+                              "name": "Card Header",
+                              "width": "fill_container",
+                              "padding": [
+                                20,
+                                20,
+                                16,
+                                20
+                              ],
+                              "gap": 4,
                               "descendants": {
-                                "q58In/Xpn7K": {
-                                  "enabled": false
+                                "fuZHB": {
+                                  "content": "Language"
                                 },
-                                "q58In/U6q13B": {
-                                  "content": "Save changes"
+                                "BZG9o": {
+                                  "content": "Default language for this Gameplane instance.",
+                                  "textGrowth": "fixed-width",
+                                  "width": "fill_container"
                                 }
                               }
+                            },
+                            {
+                              "type": "frame",
+                              "id": "m1Yjkf",
+                              "name": "Card Fields",
+                              "width": "fill_container",
+                              "layout": "vertical",
+                              "gap": 16,
+                              "padding": [
+                                0,
+                                20
+                              ],
+                              "children": [
+                                {
+                                  "type": "frame",
+                                  "id": "F8NpG0",
+                                  "name": "fieldDefaultLanguage",
+                                  "width": "fill_container",
+                                  "layout": "vertical",
+                                  "gap": 4,
+                                  "children": [
+                                    {
+                                      "type": "text",
+                                      "id": "VVbzH",
+                                      "name": "defaultLanguageLabel",
+                                      "fill": "$foreground/foreground",
+                                      "content": "Default language",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 14,
+                                      "fontWeight": "500"
+                                    },
+                                    {
+                                      "id": "hnojD",
+                                      "type": "ref",
+                                      "ref": "AT7ya",
+                                      "name": "defaultLanguageSelect",
+                                      "width": "fill_container",
+                                      "height": 40,
+                                      "descendants": {
+                                        "cFsFk": {
+                                          "content": "English",
+                                          "fill": "$foreground/foreground"
+                                        }
+                                      }
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "o7JIu4",
+                                      "name": "defaultLanguageHintWrap",
+                                      "width": "fill_container",
+                                      "padding": [
+                                        0,
+                                        4
+                                      ],
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "kNjLO",
+                                          "name": "defaultLanguageHint",
+                                          "fill": "$muted",
+                                          "textGrowth": "fixed-width",
+                                          "width": "fill_container",
+                                          "content": "Used when someone has not chosen a language and none of their browser's languages are available. Notification sinks set to Instance default use it too.",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                }
+                              ]
+                            },
+                            {
+                              "type": "frame",
+                              "id": "jfCH4",
+                              "name": "Card Actions",
+                              "width": "fill_container",
+                              "padding": [
+                                8,
+                                20,
+                                20,
+                                20
+                              ],
+                              "justifyContent": "end",
+                              "children": [
+                                {
+                                  "id": "EhcS9",
+                                  "type": "ref",
+                                  "ref": "tpKRk",
+                                  "name": "Btn Save Changes",
+                                  "descendants": {
+                                    "q58In/Xpn7K": {
+                                      "enabled": false
+                                    },
+                                    "q58In/U6q13B": {
+                                      "content": "Save changes"
+                                    }
+                                  }
+                                }
+                              ]
                             }
                           ]
                         }
@@ -34639,6 +34816,50 @@
                                           "fontFamily": "$typography/font-sans",
                                           "fontSize": 12,
                                           "fontWeight": "normal"
+                                        },
+                                        {
+                                          "type": "frame",
+                                          "id": "DTGe6",
+                                          "name": "sinkLangRow",
+                                          "gap": 8,
+                                          "padding": [
+                                            6,
+                                            0,
+                                            0,
+                                            0
+                                          ],
+                                          "alignItems": "center",
+                                          "children": [
+                                            {
+                                              "type": "text",
+                                              "id": "axNVI",
+                                              "name": "sinkLangLabel",
+                                              "fill": "$muted",
+                                              "content": "Language",
+                                              "fontFamily": "$typography/font-sans",
+                                              "fontSize": 12,
+                                              "fontWeight": "normal"
+                                            },
+                                            {
+                                              "id": "B4seX",
+                                              "type": "ref",
+                                              "ref": "AT7ya",
+                                              "name": "sinkLangSelect",
+                                              "width": 200,
+                                              "height": 32,
+                                              "padding": [
+                                                6,
+                                                10
+                                              ],
+                                              "descendants": {
+                                                "cFsFk": {
+                                                  "content": "Français",
+                                                  "fill": "$foreground/foreground",
+                                                  "fontSize": 13
+                                                }
+                                              }
+                                            }
+                                          ]
                                         }
                                       ]
                                     },
@@ -34811,6 +35032,50 @@
                                           "fontFamily": "$typography/font-sans",
                                           "fontSize": 12,
                                           "fontWeight": "normal"
+                                        },
+                                        {
+                                          "type": "frame",
+                                          "id": "TEVSf",
+                                          "name": "sinkLangRow",
+                                          "gap": 8,
+                                          "padding": [
+                                            6,
+                                            0,
+                                            0,
+                                            0
+                                          ],
+                                          "alignItems": "center",
+                                          "children": [
+                                            {
+                                              "type": "text",
+                                              "id": "NiCQX",
+                                              "name": "sinkLangLabel",
+                                              "fill": "$muted",
+                                              "content": "Language",
+                                              "fontFamily": "$typography/font-sans",
+                                              "fontSize": 12,
+                                              "fontWeight": "normal"
+                                            },
+                                            {
+                                              "id": "NCMJz",
+                                              "type": "ref",
+                                              "ref": "AT7ya",
+                                              "name": "sinkLangSelect",
+                                              "width": 200,
+                                              "height": 32,
+                                              "padding": [
+                                                6,
+                                                10
+                                              ],
+                                              "descendants": {
+                                                "cFsFk": {
+                                                  "content": "Instance default",
+                                                  "fill": "$foreground/foreground",
+                                                  "fontSize": 13
+                                                }
+                                              }
+                                            }
+                                          ]
                                         }
                                       ]
                                     },
@@ -84760,12 +85025,20 @@
       "fill": "$background/background",
       "children": [
         {
-          "id": "UQZOa",
+          "id": "gsDFd",
           "type": "ref",
           "ref": "fjQjb",
           "name": "loginL",
           "width": "fill_container",
-          "height": "fill_container"
+          "height": "fill_container",
+          "children": [
+            {
+              "id": "Xsq1h",
+              "type": "ref",
+              "ref": "CDbjX",
+              "name": "loginCard"
+            }
+          ]
         },
         {
           "id": "YTPcQ",
@@ -88478,6 +88751,29 @@
           "fontFamily": "$typography/font-sans",
           "fontSize": 11,
           "fontWeight": "normal"
+        },
+        {
+          "type": "frame",
+          "id": "onSNQ",
+          "layoutPosition": "absolute",
+          "x": 0,
+          "y": 12,
+          "name": "loginLangRow",
+          "width": 420,
+          "padding": [
+            0,
+            12
+          ],
+          "justifyContent": "end",
+          "alignItems": "center",
+          "children": [
+            {
+              "id": "uIVoY",
+              "type": "ref",
+              "ref": "Jf27F",
+              "name": "langPicker"
+            }
+          ]
         }
       ]
     },
@@ -88981,6 +89277,29 @@
               "fontWeight": "normal"
             }
           ]
+        },
+        {
+          "type": "frame",
+          "id": "Ukl0w",
+          "layoutPosition": "absolute",
+          "x": 0,
+          "y": 12,
+          "name": "shareLangRow",
+          "width": 440,
+          "padding": [
+            0,
+            12
+          ],
+          "justifyContent": "end",
+          "alignItems": "center",
+          "children": [
+            {
+              "id": "XqZ2v",
+              "type": "ref",
+              "ref": "Jf27F",
+              "name": "langPicker"
+            }
+          ]
         }
       ]
     },
@@ -99981,7 +100300,7 @@
       },
       "clip": true,
       "width": 1440,
-      "height": 2000,
+      "height": 2344,
       "fill": "$background/background",
       "children": [
         {
@@ -100191,6 +100510,257 @@
                       "layout": "vertical",
                       "gap": 16,
                       "children": [
+                        {
+                          "id": "FVPqf",
+                          "type": "ref",
+                          "ref": "XDZ0E",
+                          "name": "Card Language",
+                          "width": "fill_container",
+                          "padding": 0,
+                          "gap": 0,
+                          "children": [
+                            {
+                              "id": "E5N1t",
+                              "type": "ref",
+                              "ref": "FRpsu",
+                              "name": "Card Header",
+                              "width": "fill_container",
+                              "padding": [
+                                20,
+                                20,
+                                16,
+                                20
+                              ],
+                              "gap": 4,
+                              "descendants": {
+                                "fuZHB": {
+                                  "content": "Language"
+                                },
+                                "BZG9o": {
+                                  "content": "Choose the language of the dashboard. Your choice is saved to your account and follows you to every browser and device.",
+                                  "textGrowth": "fixed-width",
+                                  "width": "fill_container"
+                                }
+                              }
+                            },
+                            {
+                              "type": "frame",
+                              "id": "lVKGT",
+                              "name": "Card Fields",
+                              "width": "fill_container",
+                              "layout": "vertical",
+                              "gap": 16,
+                              "padding": [
+                                0,
+                                20,
+                                20,
+                                20
+                              ],
+                              "children": [
+                                {
+                                  "type": "frame",
+                                  "id": "KBpgk",
+                                  "name": "tsLangList",
+                                  "width": "fill_container",
+                                  "layout": "vertical",
+                                  "gap": 8,
+                                  "children": [
+                                    {
+                                      "type": "frame",
+                                      "id": "g2mRPb",
+                                      "name": "tsLangAuto",
+                                      "width": "fill_container",
+                                      "fill": "$field/background",
+                                      "cornerRadius": 10,
+                                      "stroke": "$border/border",
+                                      "strokeWidth": 1,
+                                      "strokeAlignment": "inner",
+                                      "gap": 12,
+                                      "padding": [
+                                        12,
+                                        14
+                                      ],
+                                      "justifyContent": "space_between",
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "id": "rbSF2",
+                                          "type": "ref",
+                                          "ref": "z2mDh",
+                                          "name": "tsLangAuto Radio",
+                                          "descendants": {
+                                            "ocqPf": {
+                                              "content": "Automatic (browser language)",
+                                              "fontWeight": "500"
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "rwNZQ",
+                                      "name": "tsLangEn",
+                                      "width": "fill_container",
+                                      "fill": "$field/background",
+                                      "cornerRadius": 10,
+                                      "stroke": "$accent/accent",
+                                      "strokeWidth": 1,
+                                      "strokeAlignment": "inner",
+                                      "gap": 12,
+                                      "padding": [
+                                        12,
+                                        14
+                                      ],
+                                      "justifyContent": "space_between",
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "id": "e5R4W",
+                                          "type": "ref",
+                                          "ref": "T8ZnV",
+                                          "name": "tsLangEn Radio",
+                                          "descendants": {
+                                            "jAx6p": {
+                                              "content": "English",
+                                              "fontWeight": "500"
+                                            }
+                                          }
+                                        },
+                                        {
+                                          "type": "text",
+                                          "id": "gdYrd",
+                                          "name": "tsLangEn Completeness",
+                                          "fill": "$muted",
+                                          "content": "100% translated",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "XxjWX",
+                                      "name": "tsLangFr",
+                                      "width": "fill_container",
+                                      "fill": "$field/background",
+                                      "cornerRadius": 10,
+                                      "stroke": "$border/border",
+                                      "strokeWidth": 1,
+                                      "strokeAlignment": "inner",
+                                      "gap": 12,
+                                      "padding": [
+                                        12,
+                                        14
+                                      ],
+                                      "justifyContent": "space_between",
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "id": "MU5SM",
+                                          "type": "ref",
+                                          "ref": "z2mDh",
+                                          "name": "tsLangFr Radio",
+                                          "descendants": {
+                                            "ocqPf": {
+                                              "content": "Français",
+                                              "fontWeight": "500"
+                                            }
+                                          }
+                                        },
+                                        {
+                                          "type": "text",
+                                          "id": "Xeuio",
+                                          "name": "tsLangFr Completeness",
+                                          "fill": "$muted",
+                                          "content": "100% translated",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "Ip3AK",
+                                      "name": "tsLangDe",
+                                      "width": "fill_container",
+                                      "fill": "$field/background",
+                                      "cornerRadius": 10,
+                                      "stroke": "$border/border",
+                                      "strokeWidth": 1,
+                                      "strokeAlignment": "inner",
+                                      "gap": 12,
+                                      "padding": [
+                                        12,
+                                        14
+                                      ],
+                                      "justifyContent": "space_between",
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "id": "VlbLF",
+                                          "type": "ref",
+                                          "ref": "z2mDh",
+                                          "name": "tsLangDe Radio",
+                                          "descendants": {
+                                            "ocqPf": {
+                                              "content": "Deutsch",
+                                              "fontWeight": "500"
+                                            }
+                                          }
+                                        },
+                                        {
+                                          "type": "text",
+                                          "id": "dl77o",
+                                          "name": "tsLangDe Completeness",
+                                          "fill": "$muted",
+                                          "content": "86% translated",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "jQ1Jm",
+                                  "name": "tsLangNote",
+                                  "width": "fill_container",
+                                  "gap": 8,
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "type": "icon",
+                                      "id": "l5IVh",
+                                      "name": "tsLangNoteIcon",
+                                      "width": 14,
+                                      "height": 14,
+                                      "icon": "info",
+                                      "library": "lucide",
+                                      "fill": "$muted"
+                                    },
+                                    {
+                                      "type": "text",
+                                      "id": "qaRbL",
+                                      "name": "tsLangNoteText",
+                                      "fill": "$muted",
+                                      "textGrowth": "fixed-width",
+                                      "width": "fill_container",
+                                      "content": "Text that has not been translated yet is shown in English.",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 12,
+                                      "fontWeight": "normal"
+                                    }
+                                  ]
+                                }
+                              ]
+                            }
+                          ]
+                        },
                         {
                           "id": "T6d1Wb",
                           "type": "ref",
@@ -101404,7 +101974,7 @@
       },
       "clip": true,
       "width": 1440,
-      "height": 2146,
+      "height": 2490,
       "fill": "$background/background",
       "children": [
         {
@@ -101629,6 +102199,257 @@
                       "layout": "vertical",
                       "gap": 16,
                       "children": [
+                        {
+                          "id": "wPAnz",
+                          "type": "ref",
+                          "ref": "XDZ0E",
+                          "name": "Card Language",
+                          "width": "fill_container",
+                          "padding": 0,
+                          "gap": 0,
+                          "children": [
+                            {
+                              "id": "UXAzi",
+                              "type": "ref",
+                              "ref": "FRpsu",
+                              "name": "Card Header",
+                              "width": "fill_container",
+                              "padding": [
+                                20,
+                                20,
+                                16,
+                                20
+                              ],
+                              "gap": 4,
+                              "descendants": {
+                                "fuZHB": {
+                                  "content": "Language"
+                                },
+                                "BZG9o": {
+                                  "content": "Choose the language of the dashboard. Your choice is saved to your account and follows you to every browser and device.",
+                                  "textGrowth": "fixed-width",
+                                  "width": "fill_container"
+                                }
+                              }
+                            },
+                            {
+                              "type": "frame",
+                              "id": "XN9Iw",
+                              "name": "Card Fields",
+                              "width": "fill_container",
+                              "layout": "vertical",
+                              "gap": 16,
+                              "padding": [
+                                0,
+                                20,
+                                20,
+                                20
+                              ],
+                              "children": [
+                                {
+                                  "type": "frame",
+                                  "id": "IA7jL",
+                                  "name": "tsLangList",
+                                  "width": "fill_container",
+                                  "layout": "vertical",
+                                  "gap": 8,
+                                  "children": [
+                                    {
+                                      "type": "frame",
+                                      "id": "lMB4u",
+                                      "name": "tsLangAuto",
+                                      "width": "fill_container",
+                                      "fill": "$field/background",
+                                      "cornerRadius": 10,
+                                      "stroke": "$border/border",
+                                      "strokeWidth": 1,
+                                      "strokeAlignment": "inner",
+                                      "gap": 12,
+                                      "padding": [
+                                        12,
+                                        14
+                                      ],
+                                      "justifyContent": "space_between",
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "id": "y2biVO",
+                                          "type": "ref",
+                                          "ref": "z2mDh",
+                                          "name": "tsLangAuto Radio",
+                                          "descendants": {
+                                            "ocqPf": {
+                                              "content": "Automatic (browser language)",
+                                              "fontWeight": "500"
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "wVLlO",
+                                      "name": "tsLangEn",
+                                      "width": "fill_container",
+                                      "fill": "$field/background",
+                                      "cornerRadius": 10,
+                                      "stroke": "$accent/accent",
+                                      "strokeWidth": 1,
+                                      "strokeAlignment": "inner",
+                                      "gap": 12,
+                                      "padding": [
+                                        12,
+                                        14
+                                      ],
+                                      "justifyContent": "space_between",
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "id": "ugSLt",
+                                          "type": "ref",
+                                          "ref": "T8ZnV",
+                                          "name": "tsLangEn Radio",
+                                          "descendants": {
+                                            "jAx6p": {
+                                              "content": "English",
+                                              "fontWeight": "500"
+                                            }
+                                          }
+                                        },
+                                        {
+                                          "type": "text",
+                                          "id": "qWkAA",
+                                          "name": "tsLangEn Completeness",
+                                          "fill": "$muted",
+                                          "content": "100% translated",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "K2VtKy",
+                                      "name": "tsLangFr",
+                                      "width": "fill_container",
+                                      "fill": "$field/background",
+                                      "cornerRadius": 10,
+                                      "stroke": "$border/border",
+                                      "strokeWidth": 1,
+                                      "strokeAlignment": "inner",
+                                      "gap": 12,
+                                      "padding": [
+                                        12,
+                                        14
+                                      ],
+                                      "justifyContent": "space_between",
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "id": "rHFAV",
+                                          "type": "ref",
+                                          "ref": "z2mDh",
+                                          "name": "tsLangFr Radio",
+                                          "descendants": {
+                                            "ocqPf": {
+                                              "content": "Français",
+                                              "fontWeight": "500"
+                                            }
+                                          }
+                                        },
+                                        {
+                                          "type": "text",
+                                          "id": "X0T6s",
+                                          "name": "tsLangFr Completeness",
+                                          "fill": "$muted",
+                                          "content": "100% translated",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "g5U051",
+                                      "name": "tsLangDe",
+                                      "width": "fill_container",
+                                      "fill": "$field/background",
+                                      "cornerRadius": 10,
+                                      "stroke": "$border/border",
+                                      "strokeWidth": 1,
+                                      "strokeAlignment": "inner",
+                                      "gap": 12,
+                                      "padding": [
+                                        12,
+                                        14
+                                      ],
+                                      "justifyContent": "space_between",
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "id": "l6VAXS",
+                                          "type": "ref",
+                                          "ref": "z2mDh",
+                                          "name": "tsLangDe Radio",
+                                          "descendants": {
+                                            "ocqPf": {
+                                              "content": "Deutsch",
+                                              "fontWeight": "500"
+                                            }
+                                          }
+                                        },
+                                        {
+                                          "type": "text",
+                                          "id": "w5Bu6x",
+                                          "name": "tsLangDe Completeness",
+                                          "fill": "$muted",
+                                          "content": "86% translated",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "H8Xcc",
+                                  "name": "tsLangNote",
+                                  "width": "fill_container",
+                                  "gap": 8,
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "type": "icon",
+                                      "id": "SozaP",
+                                      "name": "tsLangNoteIcon",
+                                      "width": 14,
+                                      "height": 14,
+                                      "icon": "info",
+                                      "library": "lucide",
+                                      "fill": "$muted"
+                                    },
+                                    {
+                                      "type": "text",
+                                      "id": "qKhih",
+                                      "name": "tsLangNoteText",
+                                      "fill": "$muted",
+                                      "textGrowth": "fixed-width",
+                                      "width": "fill_container",
+                                      "content": "Text that has not been translated yet is shown in English.",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 12,
+                                      "fontWeight": "normal"
+                                    }
+                                  ]
+                                }
+                              ]
+                            }
+                          ]
+                        },
                         {
                           "id": "eT135",
                           "type": "ref",
@@ -131192,6 +132013,1531 @@
           ]
         }
       ]
+    },
+    {
+      "type": "frame",
+      "id": "Jf27F",
+      "x": -17185,
+      "y": 26315,
+      "name": "Gameplane/Language Picker Compact",
+      "reusable": true,
+      "height": 32,
+      "cornerRadius": "$radius/3xl",
+      "gap": 6,
+      "padding": [
+        6,
+        10
+      ],
+      "alignItems": "center",
+      "children": [
+        {
+          "type": "icon",
+          "id": "G6MTRB",
+          "name": "lpGlobe",
+          "width": 14,
+          "height": 14,
+          "icon": "globe",
+          "library": "lucide",
+          "fill": "$muted"
+        },
+        {
+          "type": "text",
+          "id": "x2Vij",
+          "name": "lpLabel",
+          "fill": "$foreground/foreground",
+          "content": "English",
+          "fontFamily": "$typography/font-sans",
+          "fontSize": 13,
+          "fontWeight": "500"
+        },
+        {
+          "type": "icon",
+          "id": "ZjIo0",
+          "name": "lpChevron",
+          "width": 14,
+          "height": 14,
+          "icon": "chevron-down",
+          "library": "lucide",
+          "fill": "$muted"
+        }
+      ]
+    },
+    {
+      "type": "frame",
+      "id": "eaNkj",
+      "x": 9840,
+      "y": 23015,
+      "name": "Screen/Admin Settings — Notifications (Add sink)",
+      "theme": {
+        "semantic": "dark"
+      },
+      "clip": true,
+      "width": 1440,
+      "height": 965,
+      "fill": "$background/background",
+      "children": [
+        {
+          "id": "doJV6",
+          "type": "ref",
+          "ref": "kKFX9",
+          "height": "fill_container",
+          "descendants": {
+            "iTbd8": {
+              "fill": "#00000000"
+            },
+            "iTbd8/ghUsw": {
+              "fill": "$foreground/foreground"
+            },
+            "iTbd8/bpSQ7": {
+              "fill": "$foreground/foreground"
+            },
+            "ya5KB": {
+              "fill": "$accent/soft"
+            },
+            "ya5KB/Sr2Q5": {
+              "fill": "$accent/soft-foreground"
+            },
+            "ya5KB/Ra9NK": {
+              "fill": "$accent/soft-foreground"
+            }
+          }
+        },
+        {
+          "type": "frame",
+          "id": "wGYxe",
+          "name": "Main",
+          "width": "fill_container",
+          "height": "fill_container",
+          "fill": "$background/background",
+          "layout": "vertical",
+          "children": [
+            {
+              "id": "KI26C",
+              "type": "ref",
+              "ref": "gu5WY",
+              "width": "fill_container",
+              "descendants": {
+                "Gl7AY": {
+                  "content": "Settings"
+                }
+              }
+            },
+            {
+              "type": "frame",
+              "id": "D8np3C",
+              "name": "Body",
+              "width": "fill_container",
+              "height": "fill_container",
+              "layout": "vertical",
+              "gap": 24,
+              "padding": 24,
+              "children": [
+                {
+                  "id": "qbpRF",
+                  "type": "ref",
+                  "ref": "xCDF7",
+                  "width": "fill_container",
+                  "descendants": {
+                    "spCmk": {
+                      "content": "Admin settings"
+                    },
+                    "VbHwU": {
+                      "content": "Platform-wide configuration for this Gameplane instance."
+                    },
+                    "TgdLz": {
+                      "enabled": false
+                    }
+                  }
+                },
+                {
+                  "type": "frame",
+                  "id": "k0Dnil",
+                  "name": "Settings Layout",
+                  "width": "fill_container",
+                  "height": "fill_container",
+                  "gap": 24,
+                  "children": [
+                    {
+                      "id": "Xzvj6",
+                      "type": "ref",
+                      "ref": "Mp7Ep",
+                      "name": "Settings Nav",
+                      "width": 220,
+                      "descendants": {
+                        "eIjoV": {
+                          "fill": "#00000000"
+                        },
+                        "KSTX4": {
+                          "fill": "$surface/secondary"
+                        }
+                      }
+                    },
+                    {
+                      "id": "QvCbe",
+                      "type": "ref",
+                      "ref": "XDZ0E",
+                      "name": "Settings Panel",
+                      "width": "fill_container",
+                      "padding": 0,
+                      "gap": 0,
+                      "cornerRadius": 10,
+                      "height": "fit_content",
+                      "clip": false,
+                      "children": [
+                        {
+                          "id": "UyGwr",
+                          "type": "ref",
+                          "ref": "FRpsu",
+                          "width": "fill_container",
+                          "padding": [
+                            20,
+                            20,
+                            16,
+                            20
+                          ],
+                          "descendants": {
+                            "fuZHB": {
+                              "content": "Notifications"
+                            },
+                            "BZG9o": {
+                              "content": "Deliver server health and backup/restore events to Discord, Slack, ntfy, email, or webhooks. Credentials are entered when adding a sink and stored as a labelled Secret in the control-plane namespace.",
+                              "textGrowth": "fixed-width",
+                              "width": "fill_container"
+                            }
+                          }
+                        },
+                        {
+                          "id": "XXRhs",
+                          "type": "ref",
+                          "ref": "I9ZPb",
+                          "width": "fill_container",
+                          "padding": [
+                            0,
+                            20
+                          ],
+                          "gap": 16,
+                          "children": [
+                            {
+                              "type": "frame",
+                              "id": "CBFXu",
+                              "name": "sinkList",
+                              "width": "fill_container",
+                              "layout": "vertical",
+                              "children": [
+                                {
+                                  "type": "frame",
+                                  "id": "SVk9G",
+                                  "name": "sinkDiscord",
+                                  "width": "fill_container",
+                                  "stroke": "$border/border",
+                                  "strokeWidth": {
+                                    "bottom": 1
+                                  },
+                                  "strokeAlignment": "inner",
+                                  "gap": 12,
+                                  "padding": [
+                                    12,
+                                    0
+                                  ],
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "type": "frame",
+                                      "id": "Evfhj",
+                                      "name": "iconBox",
+                                      "width": 32,
+                                      "height": 32,
+                                      "fill": "$surface/secondary",
+                                      "cornerRadius": 6,
+                                      "justifyContent": "center",
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "type": "icon",
+                                          "id": "b6H8ig",
+                                          "width": 16,
+                                          "height": 16,
+                                          "icon": "messages-square",
+                                          "library": "lucide",
+                                          "fill": "$muted"
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "hWFRx",
+                                      "width": "fill_container",
+                                      "layout": "vertical",
+                                      "gap": 2,
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "NgjDB",
+                                          "fill": "$foreground/foreground",
+                                          "content": "ops-discord",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 14,
+                                          "fontWeight": "normal"
+                                        },
+                                        {
+                                          "type": "text",
+                                          "id": "O2W4ag",
+                                          "fill": "$muted",
+                                          "content": "discord · Secret: gameplane-notify-ops-discord",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        },
+                                        {
+                                          "type": "frame",
+                                          "id": "uSrNK",
+                                          "name": "sinkLangRow",
+                                          "gap": 8,
+                                          "padding": [
+                                            6,
+                                            0,
+                                            0,
+                                            0
+                                          ],
+                                          "alignItems": "center",
+                                          "children": [
+                                            {
+                                              "type": "text",
+                                              "id": "xhp4w",
+                                              "name": "sinkLangLabel",
+                                              "fill": "$muted",
+                                              "content": "Language",
+                                              "fontFamily": "$typography/font-sans",
+                                              "fontSize": 12,
+                                              "fontWeight": "normal"
+                                            },
+                                            {
+                                              "id": "slRXb",
+                                              "type": "ref",
+                                              "ref": "AT7ya",
+                                              "name": "sinkLangSelect",
+                                              "width": 200,
+                                              "height": 32,
+                                              "padding": [
+                                                6,
+                                                10
+                                              ],
+                                              "descendants": {
+                                                "cFsFk": {
+                                                  "content": "Français",
+                                                  "fill": "$foreground/foreground",
+                                                  "fontSize": 13
+                                                }
+                                              }
+                                            }
+                                          ]
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "shS0o",
+                                      "name": "eventChips",
+                                      "gap": 6,
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "type": "frame",
+                                          "id": "YjgGY",
+                                          "fill": "$surface/secondary",
+                                          "cornerRadius": 999,
+                                          "padding": [
+                                            2,
+                                            8
+                                          ],
+                                          "alignItems": "center",
+                                          "children": [
+                                            {
+                                              "type": "text",
+                                              "id": "pLL6W",
+                                              "fill": "$muted",
+                                              "content": "server.unhealthy",
+                                              "fontFamily": "$typography/font-sans",
+                                              "fontSize": 11,
+                                              "fontWeight": "normal"
+                                            }
+                                          ]
+                                        },
+                                        {
+                                          "type": "frame",
+                                          "id": "ktWDA",
+                                          "fill": "$surface/secondary",
+                                          "cornerRadius": 999,
+                                          "padding": [
+                                            2,
+                                            8
+                                          ],
+                                          "alignItems": "center",
+                                          "children": [
+                                            {
+                                              "type": "text",
+                                              "id": "xMeNr",
+                                              "fill": "$muted",
+                                              "content": "backup.failed",
+                                              "fontFamily": "$typography/font-sans",
+                                              "fontSize": 11,
+                                              "fontWeight": "normal"
+                                            }
+                                          ]
+                                        },
+                                        {
+                                          "type": "frame",
+                                          "id": "o5o23",
+                                          "fill": "$surface/secondary",
+                                          "cornerRadius": 999,
+                                          "padding": [
+                                            2,
+                                            8
+                                          ],
+                                          "alignItems": "center",
+                                          "children": [
+                                            {
+                                              "type": "text",
+                                              "id": "S863wb",
+                                              "fill": "$muted",
+                                              "content": "+2",
+                                              "fontFamily": "$typography/font-sans",
+                                              "fontSize": 11,
+                                              "fontWeight": "normal"
+                                            }
+                                          ]
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "id": "I97xSL",
+                                      "type": "ref",
+                                      "ref": "FIB65",
+                                      "name": "btnSendTest",
+                                      "height": 32,
+                                      "descendants": {
+                                        "K8d1zg": {
+                                          "enabled": false
+                                        },
+                                        "zMNkR": {
+                                          "content": "Send test"
+                                        }
+                                      }
+                                    },
+                                    {
+                                      "id": "bWyjr",
+                                      "type": "ref",
+                                      "ref": "hl7R3",
+                                      "name": "switchOn"
+                                    },
+                                    {
+                                      "id": "TCPlY",
+                                      "type": "ref",
+                                      "ref": "j9sz4",
+                                      "name": "btnDelete",
+                                      "width": 36,
+                                      "height": 36,
+                                      "descendants": {
+                                        "uQ9KQ": {
+                                          "icon": "trash-2"
+                                        }
+                                      }
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "d7SXt",
+                                  "name": "sinkWebhook",
+                                  "width": "fill_container",
+                                  "gap": 12,
+                                  "padding": [
+                                    12,
+                                    0
+                                  ],
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "type": "frame",
+                                      "id": "k8ZNTa",
+                                      "name": "iconBox",
+                                      "width": 32,
+                                      "height": 32,
+                                      "fill": "$surface/secondary",
+                                      "cornerRadius": 6,
+                                      "justifyContent": "center",
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "type": "icon",
+                                          "id": "bcpTb",
+                                          "width": 16,
+                                          "height": 16,
+                                          "icon": "webhook",
+                                          "library": "lucide",
+                                          "fill": "$muted"
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "HEcy8",
+                                      "width": "fill_container",
+                                      "layout": "vertical",
+                                      "gap": 2,
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "TKSOK",
+                                          "fill": "$foreground/foreground",
+                                          "content": "pager",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 14,
+                                          "fontWeight": "normal"
+                                        },
+                                        {
+                                          "type": "text",
+                                          "id": "R3i4Q",
+                                          "fill": "$muted",
+                                          "content": "webhook · no Secret configured",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 12,
+                                          "fontWeight": "normal"
+                                        },
+                                        {
+                                          "type": "frame",
+                                          "id": "ry01M",
+                                          "name": "sinkLangRow",
+                                          "gap": 8,
+                                          "padding": [
+                                            6,
+                                            0,
+                                            0,
+                                            0
+                                          ],
+                                          "alignItems": "center",
+                                          "children": [
+                                            {
+                                              "type": "text",
+                                              "id": "mXwqf",
+                                              "name": "sinkLangLabel",
+                                              "fill": "$muted",
+                                              "content": "Language",
+                                              "fontFamily": "$typography/font-sans",
+                                              "fontSize": 12,
+                                              "fontWeight": "normal"
+                                            },
+                                            {
+                                              "id": "a9PBm",
+                                              "type": "ref",
+                                              "ref": "AT7ya",
+                                              "name": "sinkLangSelect",
+                                              "width": 200,
+                                              "height": 32,
+                                              "padding": [
+                                                6,
+                                                10
+                                              ],
+                                              "descendants": {
+                                                "cFsFk": {
+                                                  "content": "Instance default",
+                                                  "fill": "$foreground/foreground",
+                                                  "fontSize": 13
+                                                }
+                                              }
+                                            }
+                                          ]
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "E39TY",
+                                      "name": "needsSecret",
+                                      "fill": "$warning/soft",
+                                      "cornerRadius": 999,
+                                      "padding": [
+                                        2,
+                                        8
+                                      ],
+                                      "justifyContent": "center",
+                                      "alignItems": "center",
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "bD8Rq",
+                                          "fill": "$warning/soft-foreground",
+                                          "content": "Needs secret",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 11,
+                                          "fontWeight": "500"
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "id": "Tgujm",
+                                      "type": "ref",
+                                      "ref": "FIB65",
+                                      "name": "btnSendTest",
+                                      "height": 32,
+                                      "opacity": 0.5,
+                                      "descendants": {
+                                        "K8d1zg": {
+                                          "enabled": false
+                                        },
+                                        "zMNkR": {
+                                          "content": "Send test"
+                                        }
+                                      }
+                                    },
+                                    {
+                                      "id": "tyv3s",
+                                      "type": "ref",
+                                      "ref": "rh2QH",
+                                      "name": "switchOff"
+                                    },
+                                    {
+                                      "id": "ZD2ij",
+                                      "type": "ref",
+                                      "ref": "j9sz4",
+                                      "name": "btnDelete",
+                                      "width": 36,
+                                      "height": 36,
+                                      "descendants": {
+                                        "uQ9KQ": {
+                                          "icon": "trash-2"
+                                        }
+                                      }
+                                    }
+                                  ]
+                                }
+                              ]
+                            },
+                            {
+                              "type": "frame",
+                              "id": "n7Y8N9",
+                              "name": "addSinkForm",
+                              "width": "fill_container",
+                              "fill": "$surface/surface",
+                              "cornerRadius": 8,
+                              "stroke": "$border/border",
+                              "strokeWidth": 1,
+                              "strokeAlignment": "inner",
+                              "layout": "vertical",
+                              "gap": 12,
+                              "padding": 16,
+                              "children": [
+                                {
+                                  "type": "text",
+                                  "id": "ZSGfk",
+                                  "name": "addSinkTitle",
+                                  "fill": "$foreground/foreground",
+                                  "content": "Add sink",
+                                  "fontFamily": "$typography/font-sans",
+                                  "fontSize": 14,
+                                  "fontWeight": "500"
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "SBeos",
+                                  "name": "addSinkRow1",
+                                  "width": "fill_container",
+                                  "gap": 12,
+                                  "children": [
+                                    {
+                                      "id": "byGF9",
+                                      "type": "ref",
+                                      "ref": "aRqX6",
+                                      "name": "fieldSinkName",
+                                      "width": "fill_container",
+                                      "descendants": {
+                                        "ANxU1": {
+                                          "content": "Name"
+                                        },
+                                        "hokJ3": {
+                                          "content": "team-alerts",
+                                          "fill": "$foreground/foreground"
+                                        },
+                                        "OiyAM": {
+                                          "width": "fill_container"
+                                        },
+                                        "wolxN": {
+                                          "content": "A short lowercase identifier (letters, digits, and dashes) used to name the sink and its Secret — like team-alerts.",
+                                          "textGrowth": "fixed-width",
+                                          "width": "fill_container"
+                                        }
+                                      }
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "m1dk4",
+                                      "name": "fieldSinkKind",
+                                      "width": "fill_container",
+                                      "layout": "vertical",
+                                      "gap": 4,
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "mb3Yd",
+                                          "name": "fieldSinkKind Label",
+                                          "fill": "$foreground/foreground",
+                                          "content": "Kind",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 14,
+                                          "fontWeight": "500"
+                                        },
+                                        {
+                                          "id": "GLWbL",
+                                          "type": "ref",
+                                          "ref": "AT7ya",
+                                          "name": "fieldSinkKind Select",
+                                          "width": "fill_container",
+                                          "height": 40,
+                                          "descendants": {
+                                            "cFsFk": {
+                                              "content": "discord",
+                                              "fill": "$foreground/foreground"
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "PjvYr",
+                                  "name": "addSinkRow2",
+                                  "width": "fill_container",
+                                  "gap": 12,
+                                  "children": [
+                                    {
+                                      "id": "bnTm0",
+                                      "type": "ref",
+                                      "ref": "aRqX6",
+                                      "name": "fieldSinkUrl",
+                                      "width": "fill_container",
+                                      "descendants": {
+                                        "ANxU1": {
+                                          "content": "Webhook URL"
+                                        },
+                                        "hokJ3": {
+                                          "content": "https://discord.com/api/webhooks/…",
+                                          "fill": "$field/placeholder"
+                                        },
+                                        "OiyAM": {
+                                          "enabled": false
+                                        }
+                                      }
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "ABfII",
+                                      "name": "fieldSinkLanguage",
+                                      "width": "fill_container",
+                                      "layout": "vertical",
+                                      "gap": 4,
+                                      "children": [
+                                        {
+                                          "type": "text",
+                                          "id": "UNBwv",
+                                          "name": "fieldSinkLanguage Label",
+                                          "fill": "$foreground/foreground",
+                                          "content": "Language",
+                                          "fontFamily": "$typography/font-sans",
+                                          "fontSize": 14,
+                                          "fontWeight": "500"
+                                        },
+                                        {
+                                          "id": "m12YV",
+                                          "type": "ref",
+                                          "ref": "AT7ya",
+                                          "name": "fieldSinkLanguage Select",
+                                          "width": "fill_container",
+                                          "height": 40,
+                                          "descendants": {
+                                            "cFsFk": {
+                                              "content": "Instance default",
+                                              "fill": "$foreground/foreground"
+                                            }
+                                          }
+                                        },
+                                        {
+                                          "type": "frame",
+                                          "id": "c8ZVI",
+                                          "name": "fieldSinkLanguage Hint Wrap",
+                                          "width": "fill_container",
+                                          "padding": [
+                                            0,
+                                            4
+                                          ],
+                                          "children": [
+                                            {
+                                              "type": "text",
+                                              "id": "tdGXR",
+                                              "name": "fieldSinkLanguage Hint",
+                                              "fill": "$muted",
+                                              "textGrowth": "fixed-width",
+                                              "width": "fill_container",
+                                              "content": "Notifications sent to this sink are written in this language.",
+                                              "fontFamily": "$typography/font-sans",
+                                              "fontSize": 12,
+                                              "fontWeight": "normal"
+                                            }
+                                          ]
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "E7eHV",
+                                  "name": "addSinkEvents",
+                                  "width": "fill_container",
+                                  "layout": "vertical",
+                                  "gap": 6,
+                                  "children": [
+                                    {
+                                      "type": "text",
+                                      "id": "Qc6AK",
+                                      "name": "addSinkEventsLabel",
+                                      "fill": "$muted",
+                                      "content": "Events (failures and recovery are pre-selected)",
+                                      "fontFamily": "$typography/font-sans",
+                                      "fontSize": 12,
+                                      "fontWeight": "normal"
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "mEY75",
+                                      "name": "addSinkEventRow",
+                                      "width": "fill_container",
+                                      "gap": 12,
+                                      "children": [
+                                        {
+                                          "type": "frame",
+                                          "id": "gG7HQ",
+                                          "name": "eventCell server.unhealthy",
+                                          "width": "fill_container",
+                                          "children": [
+                                            {
+                                              "id": "xWdJN",
+                                              "type": "ref",
+                                              "ref": "v6WNtR",
+                                              "name": "event server.unhealthy",
+                                              "descendants": {
+                                                "x7vJxB": {
+                                                  "content": "server.unhealthy",
+                                                  "fontFamily": "$typography/font-mono",
+                                                  "fontSize": 12,
+                                                  "fontWeight": "normal"
+                                                }
+                                              }
+                                            }
+                                          ]
+                                        },
+                                        {
+                                          "type": "frame",
+                                          "id": "LAkyl",
+                                          "name": "eventCell server.recovered",
+                                          "width": "fill_container",
+                                          "children": [
+                                            {
+                                              "id": "sxrMR",
+                                              "type": "ref",
+                                              "ref": "v6WNtR",
+                                              "name": "event server.recovered",
+                                              "descendants": {
+                                                "x7vJxB": {
+                                                  "content": "server.recovered",
+                                                  "fontFamily": "$typography/font-mono",
+                                                  "fontSize": 12,
+                                                  "fontWeight": "normal"
+                                                }
+                                              }
+                                            }
+                                          ]
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "hvIb3",
+                                      "name": "addSinkEventRow",
+                                      "width": "fill_container",
+                                      "gap": 12,
+                                      "children": [
+                                        {
+                                          "type": "frame",
+                                          "id": "lg04C",
+                                          "name": "eventCell backup.failed",
+                                          "width": "fill_container",
+                                          "children": [
+                                            {
+                                              "id": "Q0n3P2",
+                                              "type": "ref",
+                                              "ref": "v6WNtR",
+                                              "name": "event backup.failed",
+                                              "descendants": {
+                                                "x7vJxB": {
+                                                  "content": "backup.failed",
+                                                  "fontFamily": "$typography/font-mono",
+                                                  "fontSize": 12,
+                                                  "fontWeight": "normal"
+                                                }
+                                              }
+                                            }
+                                          ]
+                                        },
+                                        {
+                                          "type": "frame",
+                                          "id": "plcUU",
+                                          "name": "eventCell backup.succeeded",
+                                          "width": "fill_container",
+                                          "children": [
+                                            {
+                                              "id": "oIWV7",
+                                              "type": "ref",
+                                              "ref": "aOvvm",
+                                              "name": "event backup.succeeded",
+                                              "descendants": {
+                                                "rKaQI": {
+                                                  "content": "backup.succeeded",
+                                                  "fontFamily": "$typography/font-mono",
+                                                  "fontSize": 12,
+                                                  "fontWeight": "normal"
+                                                }
+                                              }
+                                            }
+                                          ]
+                                        }
+                                      ]
+                                    },
+                                    {
+                                      "type": "frame",
+                                      "id": "dQGuO",
+                                      "name": "addSinkEventRow",
+                                      "width": "fill_container",
+                                      "gap": 12,
+                                      "children": [
+                                        {
+                                          "type": "frame",
+                                          "id": "mGHDE",
+                                          "name": "eventCell restore.failed",
+                                          "width": "fill_container",
+                                          "children": [
+                                            {
+                                              "id": "hKq8k",
+                                              "type": "ref",
+                                              "ref": "v6WNtR",
+                                              "name": "event restore.failed",
+                                              "descendants": {
+                                                "x7vJxB": {
+                                                  "content": "restore.failed",
+                                                  "fontFamily": "$typography/font-mono",
+                                                  "fontSize": 12,
+                                                  "fontWeight": "normal"
+                                                }
+                                              }
+                                            }
+                                          ]
+                                        },
+                                        {
+                                          "type": "frame",
+                                          "id": "yMNPZ",
+                                          "name": "eventCell restore.succeeded",
+                                          "width": "fill_container",
+                                          "children": [
+                                            {
+                                              "id": "u73CU9",
+                                              "type": "ref",
+                                              "ref": "aOvvm",
+                                              "name": "event restore.succeeded",
+                                              "descendants": {
+                                                "rKaQI": {
+                                                  "content": "restore.succeeded",
+                                                  "fontFamily": "$typography/font-mono",
+                                                  "fontSize": 12,
+                                                  "fontWeight": "normal"
+                                                }
+                                              }
+                                            }
+                                          ]
+                                        }
+                                      ]
+                                    }
+                                  ]
+                                },
+                                {
+                                  "type": "frame",
+                                  "id": "a1MTg",
+                                  "name": "addSinkActions",
+                                  "width": "fill_container",
+                                  "gap": 8,
+                                  "justifyContent": "end",
+                                  "alignItems": "center",
+                                  "children": [
+                                    {
+                                      "id": "m63Yb",
+                                      "type": "ref",
+                                      "ref": "LMIom",
+                                      "name": "btnCancelAddSink",
+                                      "descendants": {
+                                        "vWtyO/bevQZ": {
+                                          "enabled": false
+                                        },
+                                        "vWtyO/ezEy1": {
+                                          "content": "Cancel"
+                                        }
+                                      }
+                                    },
+                                    {
+                                      "id": "lhyOq",
+                                      "type": "ref",
+                                      "ref": "tpKRk",
+                                      "name": "btnConfirmAddSink",
+                                      "descendants": {
+                                        "q58In/Xpn7K": {
+                                          "enabled": false
+                                        },
+                                        "q58In/U6q13B": {
+                                          "content": "Add sink"
+                                        }
+                                      }
+                                    }
+                                  ]
+                                }
+                              ]
+                            }
+                          ]
+                        },
+                        {
+                          "id": "P8FoV6",
+                          "type": "ref",
+                          "ref": "VvBaY",
+                          "name": "Card Actions",
+                          "width": "fill_container",
+                          "padding": [
+                            8,
+                            20,
+                            20,
+                            20
+                          ],
+                          "justifyContent": "end",
+                          "alignItems": "center",
+                          "children": [
+                            {
+                              "id": "dBGTB",
+                              "type": "ref",
+                              "ref": "tpKRk",
+                              "name": "Btn Save Changes",
+                              "descendants": {
+                                "q58In/Xpn7K": {
+                                  "enabled": false
+                                },
+                                "q58In/U6q13B": {
+                                  "content": "Save changes"
+                                }
+                              }
+                            }
+                          ]
+                        }
+                      ]
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    {
+      "type": "frame",
+      "id": "g5e2fM",
+      "x": 44960,
+      "y": -7988,
+      "name": "Screen/Mobile — Theme Settings · Language",
+      "theme": {
+        "semantic": "dark"
+      },
+      "clip": true,
+      "width": 390,
+      "height": 972,
+      "fill": "$background/background",
+      "layout": "vertical",
+      "children": [
+        {
+          "id": "DIxxO",
+          "type": "ref",
+          "ref": "fGbVF",
+          "name": "Mobile TopBar",
+          "width": "fill_container",
+          "descendants": {
+            "WOloN": {
+              "content": "Settings"
+            }
+          }
+        },
+        {
+          "type": "frame",
+          "id": "t91IL",
+          "name": "Body",
+          "width": "fill_container",
+          "fill": "$background/background",
+          "layout": "vertical",
+          "gap": 16,
+          "padding": 16,
+          "children": [
+            {
+              "id": "hArNp",
+              "type": "ref",
+              "ref": "xCDF7",
+              "name": "Page Header",
+              "width": "fill_container",
+              "descendants": {
+                "fLVEl": {
+                  "width": "fill_container"
+                },
+                "spCmk": {
+                  "content": "Theme & Appearance",
+                  "fontSize": 20
+                },
+                "VbHwU": {
+                  "content": "Personal theme presets, colors, custom CSS, and theme portability.",
+                  "textGrowth": "fixed-width",
+                  "width": "fill_container"
+                },
+                "TgdLz": {
+                  "enabled": false
+                }
+              }
+            },
+            {
+              "id": "HCLBk",
+              "type": "ref",
+              "ref": "Mp7Ep",
+              "name": "Settings Nav",
+              "width": "fill_container",
+              "descendants": {
+                "eIjoV": {
+                  "fill": "#00000000"
+                },
+                "vbQ98": {
+                  "fill": "$surface/secondary"
+                }
+              }
+            },
+            {
+              "id": "us94F",
+              "type": "ref",
+              "ref": "XDZ0E",
+              "name": "Card Language",
+              "width": "fill_container",
+              "padding": 0,
+              "gap": 0,
+              "children": [
+                {
+                  "id": "D7jwu",
+                  "type": "ref",
+                  "ref": "FRpsu",
+                  "name": "Card Header",
+                  "width": "fill_container",
+                  "padding": [
+                    20,
+                    20,
+                    16,
+                    20
+                  ],
+                  "gap": 4,
+                  "descendants": {
+                    "fuZHB": {
+                      "content": "Language"
+                    },
+                    "BZG9o": {
+                      "content": "Choose the language of the dashboard. Your choice is saved to your account and follows you to every browser and device.",
+                      "textGrowth": "fixed-width",
+                      "width": "fill_container"
+                    }
+                  }
+                },
+                {
+                  "type": "frame",
+                  "id": "b6JE8K",
+                  "name": "Card Fields",
+                  "width": "fill_container",
+                  "layout": "vertical",
+                  "gap": 16,
+                  "padding": [
+                    0,
+                    20,
+                    20,
+                    20
+                  ],
+                  "children": [
+                    {
+                      "type": "frame",
+                      "id": "D40VEw",
+                      "name": "tsLangList",
+                      "width": "fill_container",
+                      "layout": "vertical",
+                      "gap": 8,
+                      "children": [
+                        {
+                          "type": "frame",
+                          "id": "F5hpA",
+                          "name": "tsLangAuto",
+                          "width": "fill_container",
+                          "fill": "$field/background",
+                          "cornerRadius": 10,
+                          "stroke": "$border/border",
+                          "strokeWidth": 1,
+                          "strokeAlignment": "inner",
+                          "gap": 12,
+                          "padding": [
+                            12,
+                            14
+                          ],
+                          "justifyContent": "space_between",
+                          "alignItems": "center",
+                          "children": [
+                            {
+                              "id": "WqJ9R",
+                              "type": "ref",
+                              "ref": "z2mDh",
+                              "name": "tsLangAuto Radio",
+                              "descendants": {
+                                "ocqPf": {
+                                  "content": "Automatic (browser language)",
+                                  "fontWeight": "500"
+                                }
+                              }
+                            }
+                          ]
+                        },
+                        {
+                          "type": "frame",
+                          "id": "Z7fgYZ",
+                          "name": "tsLangEn",
+                          "width": "fill_container",
+                          "fill": "$field/background",
+                          "cornerRadius": 10,
+                          "stroke": "$accent/accent",
+                          "strokeWidth": 1,
+                          "strokeAlignment": "inner",
+                          "gap": 12,
+                          "padding": [
+                            12,
+                            14
+                          ],
+                          "justifyContent": "space_between",
+                          "alignItems": "center",
+                          "children": [
+                            {
+                              "id": "eLGHw",
+                              "type": "ref",
+                              "ref": "T8ZnV",
+                              "name": "tsLangEn Radio",
+                              "descendants": {
+                                "jAx6p": {
+                                  "content": "English",
+                                  "fontWeight": "500"
+                                }
+                              }
+                            },
+                            {
+                              "type": "text",
+                              "id": "uXGYj",
+                              "name": "tsLangEn Completeness",
+                              "fill": "$muted",
+                              "content": "100% translated",
+                              "fontFamily": "$typography/font-sans",
+                              "fontSize": 12,
+                              "fontWeight": "normal"
+                            }
+                          ]
+                        },
+                        {
+                          "type": "frame",
+                          "id": "hwCIe",
+                          "name": "tsLangFr",
+                          "width": "fill_container",
+                          "fill": "$field/background",
+                          "cornerRadius": 10,
+                          "stroke": "$border/border",
+                          "strokeWidth": 1,
+                          "strokeAlignment": "inner",
+                          "gap": 12,
+                          "padding": [
+                            12,
+                            14
+                          ],
+                          "justifyContent": "space_between",
+                          "alignItems": "center",
+                          "children": [
+                            {
+                              "id": "qeTNN",
+                              "type": "ref",
+                              "ref": "z2mDh",
+                              "name": "tsLangFr Radio",
+                              "descendants": {
+                                "ocqPf": {
+                                  "content": "Français",
+                                  "fontWeight": "500"
+                                }
+                              }
+                            },
+                            {
+                              "type": "text",
+                              "id": "R01hG",
+                              "name": "tsLangFr Completeness",
+                              "fill": "$muted",
+                              "content": "100% translated",
+                              "fontFamily": "$typography/font-sans",
+                              "fontSize": 12,
+                              "fontWeight": "normal"
+                            }
+                          ]
+                        },
+                        {
+                          "type": "frame",
+                          "id": "BMrZn",
+                          "name": "tsLangDe",
+                          "width": "fill_container",
+                          "fill": "$field/background",
+                          "cornerRadius": 10,
+                          "stroke": "$border/border",
+                          "strokeWidth": 1,
+                          "strokeAlignment": "inner",
+                          "gap": 12,
+                          "padding": [
+                            12,
+                            14
+                          ],
+                          "justifyContent": "space_between",
+                          "alignItems": "center",
+                          "children": [
+                            {
+                              "id": "vxJJW",
+                              "type": "ref",
+                              "ref": "z2mDh",
+                              "name": "tsLangDe Radio",
+                              "descendants": {
+                                "ocqPf": {
+                                  "content": "Deutsch",
+                                  "fontWeight": "500"
+                                }
+                              }
+                            },
+                            {
+                              "type": "text",
+                              "id": "voh3P",
+                              "name": "tsLangDe Completeness",
+                              "fill": "$muted",
+                              "content": "86% translated",
+                              "fontFamily": "$typography/font-sans",
+                              "fontSize": 12,
+                              "fontWeight": "normal"
+                            }
+                          ]
+                        }
+                      ]
+                    },
+                    {
+                      "type": "frame",
+                      "id": "F5QWwF",
+                      "name": "tsLangNote",
+                      "width": "fill_container",
+                      "gap": 8,
+                      "alignItems": "center",
+                      "children": [
+                        {
+                          "type": "icon",
+                          "id": "P0J8GB",
+                          "name": "tsLangNoteIcon",
+                          "width": 14,
+                          "height": 14,
+                          "icon": "info",
+                          "library": "lucide",
+                          "fill": "$muted"
+                        },
+                        {
+                          "type": "text",
+                          "id": "pTutL",
+                          "name": "tsLangNoteText",
+                          "fill": "$muted",
+                          "textGrowth": "fixed-width",
+                          "width": "fill_container",
+                          "content": "Text that has not been translated yet is shown in English.",
+                          "fontFamily": "$typography/font-sans",
+                          "fontSize": 12,
+                          "fontWeight": "normal"
+                        }
+                      ]
+                    }
+                  ]
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    {
+      "type": "frame",
+      "id": "CDbjX",
+      "x": -10998.0544367535,
+      "y": 27592.997924316056,
+      "name": "Gameplane/Login Card With Language",
+      "reusable": true,
+      "width": 420,
+      "children": [
+        {
+          "id": "g8k7AO",
+          "type": "ref",
+          "ref": "J14ME",
+          "name": "loginCard",
+          "width": "fill_container"
+        },
+        {
+          "type": "frame",
+          "id": "L3y9E",
+          "layoutPosition": "absolute",
+          "x": 0,
+          "y": 12,
+          "name": "loginLangRow",
+          "width": 420,
+          "padding": [
+            0,
+            12
+          ],
+          "justifyContent": "end",
+          "alignItems": "center",
+          "children": [
+            {
+              "id": "c7DCx",
+              "type": "ref",
+              "ref": "Jf27F",
+              "name": "langPicker"
+            }
+          ]
+        }
+      ]
+    },
+    {
+      "type": "frame",
+      "id": "G7OwqK",
+      "x": 8200,
+      "y": 4500,
+      "name": "Screen/Login — Language menu open",
+      "theme": {
+        "semantic": "dark"
+      },
+      "clip": true,
+      "width": 1440,
+      "height": 900,
+      "fill": "$background/background",
+      "children": [
+        {
+          "id": "knE8K",
+          "type": "ref",
+          "ref": "fjQjb",
+          "name": "loginL",
+          "width": "fill_container",
+          "height": "fill_container",
+          "children": [
+            {
+              "id": "g5PgR",
+              "type": "ref",
+              "ref": "CDbjX",
+              "name": "loginCard"
+            }
+          ]
+        },
+        {
+          "id": "uERm8",
+          "type": "ref",
+          "ref": "T8Hug",
+          "name": "loginR",
+          "width": "fill_container",
+          "height": "fill_container"
+        },
+        {
+          "type": "frame",
+          "id": "IbjMm",
+          "layoutPosition": "absolute",
+          "x": 388,
+          "y": 184,
+          "name": "langMenu",
+          "width": 170,
+          "fill": "$surface/surface",
+          "cornerRadius": "$radius/md",
+          "stroke": "$border/border",
+          "strokeWidth": 1,
+          "strokeAlignment": "inner",
+          "effect": {
+            "type": "shadow",
+            "shadowType": "outer",
+            "color": "#00000059",
+            "offset": {
+              "x": 0,
+              "y": 4
+            },
+            "blur": 12
+          },
+          "layout": "vertical",
+          "padding": 4,
+          "children": [
+            {
+              "id": "g6idK",
+              "type": "ref",
+              "ref": "B5sYje",
+              "name": "langItemEnglish",
+              "width": "fill_container",
+              "descendants": {
+                "ghUsw": {
+                  "icon": "check"
+                },
+                "bpSQ7": {
+                  "content": "English",
+                  "fontFamily": "$typography/font-sans"
+                }
+              }
+            },
+            {
+              "id": "t5NvrH",
+              "type": "ref",
+              "ref": "W8XiN",
+              "name": "langItemFrancais",
+              "width": "fill_container",
+              "descendants": {
+                "Sr2Q5": {
+                  "opacity": 0
+                },
+                "Ra9NK": {
+                  "content": "Français"
+                }
+              }
+            },
+            {
+              "id": "ekh8P",
+              "type": "ref",
+              "ref": "W8XiN",
+              "name": "langItemDeutsch",
+              "width": "fill_container",
+              "descendants": {
+                "Sr2Q5": {
+                  "opacity": 0
+                },
+                "Ra9NK": {
+                  "content": "Deutsch"
+                }
+              }
+            }
+          ]
+        }
+      ]
     }
   ],
   "themes": {
diff --git a/docs/agent-architecture.md b/docs/agent-architecture.md
index bc9ebcd00..02e2a47e5 100644
--- a/docs/agent-architecture.md
+++ b/docs/agent-architecture.md
@@ -42,6 +42,12 @@ This document is the **first stop** for AI agents modifying or extending Gamepla
 | **Modules** | `modules/<game>/specs.md` | OCI bundle templates for deploying specific games (e.g., Minecraft, Rust). |
 | **Test e2e** | `test/e2e/specs.md` | E2E integration test suite covering operator and API flows. |
 
+## Task to doc map
+
+| Task | Read |
+| --- | --- |
+| Translations, language packs, localized server or module messages (i18n) | `docs/translating.md`, `specs/019-localization-language-packs/contracts/` (`pack-format.md`, `server-messages.md`, `i18n-api.md`, `module-locales.md`, `check-tool.md`), and the Internationalization section of `web/specs.md` |
+
 ## How to use this index
 1. Identify the domain of your task (e.g., "Add an auth provider").
 2. Find the component handling this domain (e.g., "API Gateway").
diff --git a/docs/architecture.md b/docs/architecture.md
index cc9ccb2fe..29219af3b 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -289,6 +289,15 @@ bundle upload) only reads and writes these CRs/ConfigMaps; the
 operator owns all reconciliation, so the dashboard and kubectl always
 converge on the same outcome. Format spec: `docs/module-authoring.md`.
 
+## Internationalization
+
+Language packs are shared: `i18n/locales/<tag>/{app.json,meta.json}` is embedded in Go (`i18n/catalog`, used by the API and operator) and compiled for the dashboard (`web/scripts/i18n-compile.mjs`). One checker (`i18n/cmd/i18n-check`) validates packs and computes the manifest (`languages.json`), including the listing rule (completeness at least 80%, left-to-right, never `en-XA`), so every component agrees on which languages exist. Contributor guide: `docs/translating.md`.
+
+- **API.** Error responses stay English plain text unless the request lists `application/problem+json` in `Accept` (opt-in); then the body is RFC 9457 with a stable `messageId` and `args` extensions and the English text in `detail`. Users save a language (`PUT /users/me/language`), admins set the instance default (`GET /auth/locale` exposes only that), and each notification destination can carry its own language.
+- **Operator.** Conditions keep their English `message`; the arguments interpolated into it are written to `status.conditionArgs[<Type>]`, and the dashboard translates `condition.<type>.<reason>` with them. The operator never depends on a UI language.
+- **Module translations.** The Module reconciler validates a bundle's `locales/<tag>.json` against ids derived from its templates and writes the valid entries to the `<template>-locales` ConfigMap; the API serves them at `GET /modules/{name}/locales/{tag}`. Invalid or oversized files are reported by the `LocalesValid` condition and never fail an install.
+- **Dashboard runtime.** `I18nProvider` resolves the language (saved choice, browser choice, `navigator.languages`, instance default, `en`), lazy-loads the compiled catalog chunk and re-renders without remounting routes. Missing messages fall back to English. Details: `web/specs.md`.
+
 ## Multi-cluster (federation)
 
 Gameplane scales across multiple Kubernetes clusters through a
diff --git a/docs/contributing.md b/docs/contributing.md
index 406df1f52..ad30c718d 100644
--- a/docs/contributing.md
+++ b/docs/contributing.md
@@ -151,6 +151,15 @@ work on your own fork of a submodule, repoint it locally:
 `git submodule set-url modules https://github.com/<you>/module.git`
 (don't commit that change).
 
+## Translating
+
+Language packs live in `i18n/locales/<tag>/`. Adding a language or
+improving one does not need code changes. See
+[`docs/translating.md`](translating.md) for the folder layout, the message
+rules, the 80% listing threshold, and how to check a pack. A PR that touches
+only `i18n/locales/**` and has no type prefix in its title is labelled
+`type: docs` and `area: shared`.
+
 ## Code review
 
 PRs receive an automated advisory review from the CodeRabbit GitHub App, configured by `.coderabbit.yaml`. CodeRabbit's rules encode the repo's style guide and house rules — wrapping errors with `%w`, no unjustified `any`, fix rather than silence linter warnings, etc. Its feedback does not block merges. If you think a rule is wrong, raise it with the maintainers rather than working around it — this keeps the rules canonical and consistent across the codebase.
diff --git a/docs/module-authoring.md b/docs/module-authoring.md
index 0e54f6566..1141965bb 100644
--- a/docs/module-authoring.md
+++ b/docs/module-authoring.md
@@ -194,6 +194,41 @@ A module bundle is a single OCI artifact:
 | `template.yaml`  | yes      | `application/vnd.gameplane.module.template.v1+yaml`     |
 | `README.md`      | no       | `application/vnd.gameplane.module.readme.v1+md`         |
 | `icon.png`       | no       | `image/png`                                           |
+| `locales/<tag>.json` | no   | `application/vnd.gameplane.module.locale.v1+json`       |
+
+Translations live in a `locales/` directory next to `module.yaml`. Each
+`locales/<tag>.json` (for example `fr.json` or `pt-BR.json`) maps message ids to
+`{"defaultMessage": "..."}` entries and becomes one layer titled
+`locales/<tag>.json`. Run `gp-module i18n extract` to write the English
+reference `locales/en.json` (every id with a translator description); it is
+not shipped. `gp-module validate` checks translations against it. On install
+the operator keeps the valid entries, drops invalid ones, and reports them on
+the GameTemplate as the `LocalesValid` condition and a Warning event; they never
+fail the install.
+
+Every module source carries the same files:
+
+| Source | Where `locales/<tag>.json` lives |
+| --- | --- |
+| OCI | one layer per file (title `locales/<tag>.json`) |
+| directory, local, git, HTTP archive | `locales/<tag>.json` in the module directory |
+| upload | ConfigMap key `locales.<tag>.json`; an uploaded archive may contain `locales/<tag>.json`, counted in the 900 KiB bundle limit |
+| `gp-module package --output` | the `.tar.gz` contains `locales/<tag>.json` (`en.json` excluded) |
+
+A translation file larger than 900 KiB is not read, and neither is a
+language that would take all of a bundle's translation files past 4 MiB
+together (languages count in file-name order); the install still
+succeeds and the `LocalesValid` condition shows `LocalesTooLarge` naming the
+language. The condition reasons are `Valid`, `InvalidEntries`,
+`LocalesTooLarge` and `WriteFailed`; when several apply, `WriteFailed` wins,
+then `LocalesTooLarge`, then `InvalidEntries`. Warning
+events fire only when the list of problems changes, not on every re-pull.
+
+Message ids may contain upper case letters (for example
+`config.MAX_PLAYERS.displayName`) and `~` as the reversible escapes `~0` and
+`~1`. Run `gp-module i18n stamp` after translating to record the English text
+each entry was made from (`sourceHash`); if the English text changes later,
+`gp-module validate` warns with `locale-needs-review`.
 
 Manifest:
 
@@ -239,7 +274,8 @@ oras push \
   module.yaml:application/vnd.gameplane.module.metadata.v1+yaml \
   template.yaml:application/vnd.gameplane.module.template.v1+yaml \
   README.md:application/vnd.gameplane.module.readme.v1+md \
-  icon.png:image/png
+  icon.png:image/png \
+  locales/fr.json:application/vnd.gameplane.module.locale.v1+json
 ```
 
 Private registries: log in once with `oras login <registry>`. The cluster
diff --git a/docs/notifications.md b/docs/notifications.md
index 676c1f19a..593341e10 100644
--- a/docs/notifications.md
+++ b/docs/notifications.md
@@ -99,7 +99,10 @@ connection, so `tls: none` only works for unauthenticated relays.
     "namespace": "gameplane-games",
     "message": "restic exited with code 1",
     "instance": "prod",
-    "test": false
+    "test": false,
+    "language": "en",
+    "title": "[prod] backup failed: gameplane-games/nightly",
+    "text": "[prod] backup failed: gameplane-games/nightly — restic exited with code 1"
   }
   ```
 
@@ -108,6 +111,22 @@ connection, so `tls: none` only works for unauthenticated relays.
 `instance` is **Admin Settings → General → Instance name**, so alerts from
 different Gameplane installs are tellable apart.
 
+## Language
+
+Each destination can have its own language. Set `"language": "<tag>"` on the
+sink in `PUT /admin/config/notifications`, or pick it in the destination form
+when that is available. Leave it out to use the instance default language
+(**Admin Settings → Language**, the `i18n` config section), which falls back to
+English. A tag that this release does not offer is rejected with `400` and the
+message id `server.i18n.unknown_language`. The headline (`title`) and the fixed
+sentences (for example the test-send body) are translated; the Kubernetes
+`reason` and `message` of an event are quoted verbatim in English. The test
+send (`POST /admin/notifications/sinks/{name}/test`) uses the destination's
+language.
+
+`language`, `title` and `text` are additive: every other field keeps its name
+and value. `language` is the language the text was rendered in.
+
 ## Testing a sink
 
 `POST /admin/notifications/sinks/{name}/test` (permission `config:manage`)
diff --git a/docs/translating.md b/docs/translating.md
new file mode 100644
index 000000000..daac14fb7
--- /dev/null
+++ b/docs/translating.md
@@ -0,0 +1,195 @@
+# Translating Gameplane
+
+Gameplane's dashboard and its server messages are translated into other
+languages. Each language is a **language pack**: a folder under
+`i18n/locales/` with two JSON files. You do not need to write code to add
+one. This guide covers the folder layout, the message rules, how to check
+your work, and when a language shows in the picker.
+
+Translations are welcome as a partial pack. A pack merges even when it is
+not finished. It stays hidden from users until enough of it is translated.
+
+## Folder layout
+
+```
+i18n/locales/
+  en/          English reference. Generated. Do not hand-edit app.json.
+    app.json
+    meta.json
+  fr/          your language, tag "fr"
+    app.json
+    meta.json
+```
+
+To start a language, copy the whole `i18n/locales/en/` folder to
+`i18n/locales/<tag>/`. Use a BCP 47 tag such as `fr`, `pt-BR`, or `sr-Latn`.
+The folder name must equal the `tag` in `meta.json`.
+
+### app.json
+
+`app.json` maps each message id to an entry:
+
+```json
+{
+  "condition.addressassignment.assigned": {
+    "defaultMessage": "{assignedFrom, select, pool {Address {address} assigned from pool ''{pool}''.} other {Address {address} assigned.}}",
+    "description": "AddressAssignment condition once an address is assigned. assignedFrom is pool or default."
+  }
+}
+```
+
+- Replace `defaultMessage` with your translation. Keep `description` as it
+  is. The description is for translators and is not shown in the app.
+- Keys are sorted by id. Keep them sorted when you add or move entries.
+- Use 2-space indentation, UTF-8, and end the file with a newline.
+- Do not invent ids. An id that English does not have is an error. You may
+  leave out any id you have not translated yet.
+- `sourceHash` is written by the checker. It records which English text
+  your translation was made from. Leave it alone when you edit by hand.
+
+### meta.json
+
+`meta.json` describes the language:
+
+```json
+{
+  "tag": "fr",
+  "nativeName": "Français",
+  "englishName": "French",
+  "direction": "ltr",
+  "credits": [{ "name": "Ada Example", "url": "https://example.org" }]
+}
+```
+
+- `tag` must equal the folder name.
+- `nativeName` is the name of the language in that language. `englishName`
+  is the name in English.
+- `direction` is `ltr` or `rtl`. A language with `rtl` merges but is not
+  listed in the picker yet.
+- `credits` is optional. Add yourself here.
+- Unknown keys are rejected.
+
+## Message rules
+
+Messages use ICU MessageFormat. Follow these rules:
+
+- Keep every placeholder that English has. Use the same names, such as
+  `{name}`. The order can change.
+- Do not add a placeholder that English does not have.
+- Date and number formats keep their form, such as `{d, date, short}` and
+  `{n, number}`.
+- A literal apostrophe next to a placeholder is written twice, as in
+  `''{pool}''`. Copy the English quoting.
+- Plurals follow the rules of your language. Use the `other` category. It
+  is required. For example:
+
+  ```
+  {n, plural, one {# serveur} other {# serveurs}}
+  ```
+
+- `{x, select, ...}` also works, as in the example above. Keep the `other`
+  option.
+- You may use `<b>…</b>` and `<link>…</link>` tags. Do not use any other
+  tag, HTML entity, `javascript:` link, or `<script`. The checker rejects
+  them.
+
+## Glossary and style
+
+- Use a neutral, plain tone. Keep sentences short.
+- Do not translate these terms. Keep them as written in English:
+  Gameplane, GameServer, GameTemplate, Backup, BackupSchedule, Restore,
+  Cluster, Module, ModuleSource, NetworkCapture, Kubernetes, LoadBalancer.
+  These are resource kinds and product names.
+- Do not invent fixed translations for product words. Ask in the pull
+  request if a term is unclear.
+- Keep button labels short. Match the length of the English text when you
+  can, because the layout is tight.
+
+## Check your pack
+
+Run the checker from the `i18n/` folder to see findings on your pack:
+
+```sh
+cd i18n
+go run ./cmd/i18n-check locales
+```
+
+The checker exits with one of these codes:
+
+| Exit | Meaning |
+|---|---|
+| 0 | No errors found |
+| 1 | At least one finding |
+| 2 | Usage error, or a required file could not be read |
+
+Findings use these codes:
+
+| Code | Severity | What it means |
+|---|---|---|
+| `malformed-pack` | error | `app.json` is not valid JSON or has the wrong shape |
+| `invalid-meta` | error | `meta.json` is missing a field, has an unknown key, or the tag does not match the folder |
+| `icu-syntax` | error | The message does not parse as ICU MessageFormat |
+| `missing-placeholder` | error | A placeholder from English is missing |
+| `extra-placeholder` | error | A placeholder that English does not have |
+| `markup` | error | A tag or entity that is not allowed |
+| `unknown-id` | error | The id is not in English. Remove the entry |
+| `needs-review` | info | English changed after your translation was made. The entry still shows |
+
+Partial packs are fine. A missing id is not a finding. English shows for it.
+
+The checker has more options:
+
+- `--base <dir>` compares completeness with an older copy of the packs.
+- `--summary <file>` writes a markdown summary.
+- `--stamp` adds `sourceHash` to translated entries that lack one.
+- `--manifest <file>` writes the language list as JSON.
+
+You can run the checker on your machine to see findings early. It is not a
+test suite. CI runs it on every pull request. The job summary shows your
+pack's completeness before and after your change.
+
+## When a language shows in the picker
+
+A language is listed in the picker only when both of these are true:
+
+- At least **80%** of the English messages have a usable translation.
+  Entries marked `needs-review` count as usable.
+- The direction is `ltr`.
+
+A pack under 80% still merges. It stays hidden until more of it is done.
+Maintainers can change the 80% threshold.
+
+The dashboard reads the list of languages from a generated manifest. A pack
+under 80% will not appear in the picker. To rebuild the manifest and the
+compiled packs, run these commands in `web/` (they need Go installed), then
+start the dev server with `make web-dev`:
+
+```sh
+cd web
+npm run i18n:manifest
+npm run i18n:compile
+```
+
+The build keeps only the entries the checker accepts. Any other entry
+shows English.
+
+## Review and merge
+
+1. Open a pull request with your pack. Use a `feat:` or `docs:` title, for
+   example `feat: add French language pack`.
+2. CI runs the checker and posts the completeness in the job summary.
+3. A maintainer or a designated language reviewer checks the wording. The
+   pull request needs one human approval before it merges.
+4. A pull request that changes only `i18n/locales/**` gets `area: shared`
+   from the auto-label workflow. If its title has no type prefix, it also
+   gets `type: docs`. Add a `docs:` prefix to be sure.
+
+Translations made with Weblate are also planned. The Weblate project link
+will be added here once the project exists. Only translations that a
+human reviewer approves are merged. They arrive as a pull request from the
+`weblate/translations` branch and pass the same checks.
+
+## Related docs
+
+- [Contributing](contributing.md): the general pull request process.
+- [`i18n/specs.md`](../i18n/specs.md): the design of the language packs.
diff --git a/go.work b/go.work
index 69a166196..fa6b1bb44 100644
--- a/go.work
+++ b/go.work
@@ -8,6 +8,7 @@ use (
 	./gameaction
 	./gameproto
 	./gp-module
+	./i18n
 	./mcp-server
 	./netguard
 	./operator
diff --git a/gp-module/cmd/gp-module/i18n.go b/gp-module/cmd/gp-module/i18n.go
new file mode 100644
index 000000000..6b9a7f7b2
--- /dev/null
+++ b/gp-module/cmd/gp-module/i18n.go
@@ -0,0 +1,125 @@
+// Package main implements the gp-module CLI.
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	gpi18n "github.com/GameplanePanel/gameplane/gp-module/internal/i18n"
+)
+
+func runI18n(args []string) {
+	os.Exit(i18nCommand(args, os.Stdout, os.Stderr))
+}
+
+// i18nCommand runs the i18n subcommands and returns the process exit code:
+// 0 on success, 1 on error, 2 on usage errors.
+func i18nCommand(args []string, stdout, stderr io.Writer) int {
+	if len(args) == 0 || args[0] == "-h" || args[0] == "--help" {
+		_, _ = fmt.Fprint(stderr, i18nUsage)
+		if len(args) == 0 {
+			return 2
+		}
+		return 0
+	}
+	switch args[0] {
+	case "extract":
+		return i18nExtract(args[1:], stdout, stderr)
+	case "stamp":
+		return i18nStamp(args[1:], stdout, stderr)
+	default:
+		_, _ = fmt.Fprintf(stderr, "error: unknown i18n subcommand %q\n\n%s", args[0], i18nUsage)
+		return 2
+	}
+}
+
+const i18nUsage = `Usage: gp-module i18n <subcommand> [arguments]
+
+Subcommands:
+  extract [MODULE_PATH] [--output <file>]
+      Derive the translatable message ids from module.yaml and template.yaml
+      and write the English reference pack, with translator descriptions
+      (default: <MODULE_PATH>/locales/en.json).
+  stamp [MODULE_PATH]
+      Record the current English text hash (sourceHash) on every translated
+      entry of <MODULE_PATH>/locales/<tag>.json (except en.json) that lacks
+      one, so a later English change shows up as needs-review.
+`
+
+func i18nExtract(args []string, stdout, stderr io.Writer) int {
+	var (
+		modulePath = "."
+		output     string
+		havePath   bool
+	)
+	for i := 0; i < len(args); i++ {
+		arg := args[i]
+		switch {
+		case arg == "-h" || arg == "--help":
+			_, _ = fmt.Fprint(stderr, i18nUsage)
+			return 0
+		case arg == "--output" || arg == "-output":
+			if i+1 < len(args) {
+				output = args[i+1]
+				i++
+				continue
+			}
+			_, _ = fmt.Fprintln(stderr, "error: --output needs a file path")
+			return 2
+		case strings.HasPrefix(arg, "--output="):
+			output = strings.TrimPrefix(arg, "--output=")
+		case strings.HasPrefix(arg, "-"):
+			_, _ = fmt.Fprintf(stderr, "error: unknown option %q\n\n%s", arg, i18nUsage)
+			return 2
+		default:
+			if havePath {
+				_, _ = fmt.Fprintln(stderr, "error: only one MODULE_PATH may be given")
+				return 2
+			}
+			modulePath, havePath = arg, true
+		}
+	}
+	written, err := gpi18n.WriteExtract(modulePath, output)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "error: %v\n", err)
+		return 1
+	}
+	_, _ = fmt.Fprintf(stdout, "wrote %s\n", written)
+	return 0
+}
+
+func i18nStamp(args []string, stdout, stderr io.Writer) int {
+	modulePath := "."
+	havePath := false
+	for _, arg := range args {
+		switch {
+		case arg == "-h" || arg == "--help":
+			_, _ = fmt.Fprint(stderr, i18nUsage)
+			return 0
+		case strings.HasPrefix(arg, "-"):
+			_, _ = fmt.Fprintf(stderr, "error: unknown option %q\n\n%s", arg, i18nUsage)
+			return 2
+		default:
+			if havePath {
+				_, _ = fmt.Fprintln(stderr, "error: only one MODULE_PATH may be given")
+				return 2
+			}
+			modulePath, havePath = arg, true
+		}
+	}
+	stamped, err := gpi18n.Stamp(modulePath)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "error: %v\n", err)
+		return 1
+	}
+	if len(stamped) == 0 {
+		_, _ = fmt.Fprintln(stdout, "nothing to stamp")
+		return 0
+	}
+	for _, f := range stamped {
+		_, _ = fmt.Fprintf(stdout, "stamped %s\n", f)
+	}
+	return 0
+}
diff --git a/gp-module/cmd/gp-module/i18n_stamp_test.go b/gp-module/cmd/gp-module/i18n_stamp_test.go
new file mode 100644
index 000000000..398d83e8a
--- /dev/null
+++ b/gp-module/cmd/gp-module/i18n_stamp_test.go
@@ -0,0 +1,46 @@
+package main
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestI18nStampCommand(t *testing.T) {
+	t.Parallel()
+	dir := i18nModule(t)
+	if err := os.MkdirAll(filepath.Join(dir, "locales"), 0o750); err != nil {
+		t.Fatal(err)
+	}
+	fr := filepath.Join(dir, "locales", "fr.json")
+	if err := os.WriteFile(fr, []byte(`{"template.displayName":{"defaultMessage":"Jeu"}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	var out, errb bytes.Buffer
+	if got := i18nCommand([]string{"stamp", dir}, &out, &errb); got != 0 || !strings.Contains(out.String(), "stamped") {
+		t.Fatalf("exit = %d out=%q err=%q", got, out.String(), errb.String())
+	}
+	if data, _ := os.ReadFile(fr); !strings.Contains(string(data), "sourceHash") {
+		t.Errorf("fr.json = %s", data)
+	}
+	out.Reset()
+	if got := i18nCommand([]string{"stamp", dir}, &out, &errb); got != 0 || !strings.Contains(out.String(), "nothing to stamp") {
+		t.Fatalf("second run exit = %d out=%q", got, out.String())
+	}
+}
+
+func TestI18nStampUsageErrors(t *testing.T) {
+	t.Parallel()
+	var out, errb bytes.Buffer
+	if got := i18nCommand([]string{"stamp", "--nope"}, &out, &errb); got != 2 {
+		t.Errorf("unknown option exit = %d", got)
+	}
+	if got := i18nCommand([]string{"stamp", "a", "b"}, &out, &errb); got != 2 {
+		t.Errorf("two paths exit = %d", got)
+	}
+	if got := i18nCommand([]string{"stamp", filepath.Join(t.TempDir(), "missing")}, &out, &errb); got != 1 {
+		t.Errorf("missing module exit = %d", got)
+	}
+}
diff --git a/gp-module/cmd/gp-module/i18n_test.go b/gp-module/cmd/gp-module/i18n_test.go
new file mode 100644
index 000000000..6644d5597
--- /dev/null
+++ b/gp-module/cmd/gp-module/i18n_test.go
@@ -0,0 +1,91 @@
+package main
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func i18nModule(t *testing.T) string {
+	t.Helper()
+	dir := t.TempDir()
+	files := map[string]string{
+		"module.yaml":   "name: demo\ndisplayName: Demo\n",
+		"template.yaml": "spec:\n  displayName: Demo Game\n",
+	}
+	for name, body := range files {
+		if err := os.WriteFile(filepath.Join(dir, name), []byte(body), 0o600); err != nil {
+			t.Fatal(err)
+		}
+	}
+	return dir
+}
+
+func TestI18nCommandUsage(t *testing.T) {
+	t.Parallel()
+	var out, errb bytes.Buffer
+	if got := i18nCommand(nil, &out, &errb); got != 2 {
+		t.Errorf("no args exit = %d", got)
+	}
+	errb.Reset()
+	if got := i18nCommand([]string{"--help"}, &out, &errb); got != 0 || !strings.Contains(errb.String(), "extract") {
+		t.Errorf("help exit = %d: %s", got, errb.String())
+	}
+	if got := i18nCommand([]string{"nope"}, &out, &errb); got != 2 {
+		t.Errorf("unknown subcommand exit = %d", got)
+	}
+}
+
+func TestI18nExtractWritesDefaultFile(t *testing.T) {
+	t.Parallel()
+	dir := i18nModule(t)
+	var out, errb bytes.Buffer
+	if got := i18nCommand([]string{"extract", dir}, &out, &errb); got != 0 {
+		t.Fatalf("exit = %d: %s", got, errb.String())
+	}
+	data, err := os.ReadFile(filepath.Join(dir, "locales", "en.json"))
+	if err != nil || !strings.Contains(string(data), "template.displayName") {
+		t.Fatalf("en.json: %v %s", err, data)
+	}
+}
+
+func TestI18nExtractOutputFlagForms(t *testing.T) {
+	t.Parallel()
+	dir := i18nModule(t)
+	for _, args := range [][]string{
+		{"extract", "--output", filepath.Join(dir, "a.json"), dir},
+		{"extract", dir, "--output=" + filepath.Join(dir, "b.json")},
+	} {
+		var out, errb bytes.Buffer
+		if got := i18nCommand(args, &out, &errb); got != 0 {
+			t.Fatalf("%v exit = %d: %s", args, got, errb.String())
+		}
+	}
+	for _, name := range []string{"a.json", "b.json"} {
+		if _, err := os.Stat(filepath.Join(dir, name)); err != nil {
+			t.Error(err)
+		}
+	}
+}
+
+func TestI18nExtractErrors(t *testing.T) {
+	t.Parallel()
+	cases := []struct {
+		args []string
+		want int
+	}{
+		{[]string{"extract", "--output"}, 2},
+		{[]string{"extract", "--bogus"}, 2},
+		{[]string{"extract", "a", "b"}, 2},
+		{[]string{"extract", filepath.Join(t.TempDir(), "empty")}, 1},
+		{[]string{"extract", "-h"}, 0},
+	}
+	for _, c := range cases {
+		var out, errb bytes.Buffer
+		if got := i18nCommand(c.args, &out, &errb); got != c.want {
+			t.Errorf("%v exit = %d, want %d (%s)", c.args, got, c.want, errb.String())
+		}
+	}
+}
diff --git a/gp-module/cmd/gp-module/main.go b/gp-module/cmd/gp-module/main.go
index c687a10d0..3313270c4 100644
--- a/gp-module/cmd/gp-module/main.go
+++ b/gp-module/cmd/gp-module/main.go
@@ -23,6 +23,7 @@ Commands:
   validate  Offline validation and linting of module manifests
   preview   Dry-run manifest rendering and dynamic config preview
   package   Package module directory into an OCI artifact bundle
+  i18n      Extract and manage module translations
 
 Options:
   -h, --help     Show this help message
@@ -56,6 +57,8 @@ func main() {
 		runPreview(args)
 	case "package", "build", "bundle":
 		runPackage(args)
+	case "i18n":
+		runI18n(args)
 	default:
 		fmt.Fprintf(os.Stderr, "error: unknown command %q\n\n", cmd)
 		printUsage()
diff --git a/gp-module/go.mod b/gp-module/go.mod
index 494d52bd5..4e1826572 100644
--- a/gp-module/go.mod
+++ b/gp-module/go.mod
@@ -2,12 +2,20 @@ module github.com/GameplanePanel/gameplane/gp-module
 
 go 1.26.0
 
-require gopkg.in/yaml.v3 v3.0.1
+// i18n is an in-repo module (no published version); resolve it locally
+// both inside the go.work workspace and in standalone/Docker builds.
+replace github.com/GameplanePanel/gameplane/i18n => ../i18n
+
+require (
+	github.com/GameplanePanel/gameplane/i18n v0.0.0
+	gopkg.in/yaml.v3 v3.0.1
+)
 
 require (
 	github.com/fxamacker/cbor/v2 v2.9.2 // indirect
 	github.com/kr/text v0.2.0 // indirect
 	github.com/x448/float16 v0.8.4 // indirect
+	golang.org/x/text v0.42.0 // indirect
 	gopkg.in/inf.v0 v0.9.1 // indirect
 	k8s.io/apimachinery v0.37.1
 	k8s.io/utils v0.0.0-20260707023825-cf1189d6abe3 // indirect
diff --git a/gp-module/go.sum b/gp-module/go.sum
index dc46936d7..df8edf942 100644
--- a/gp-module/go.sum
+++ b/gp-module/go.sum
@@ -13,6 +13,8 @@ github.com/spf13/pflag v1.0.10 h1:4EBh2KAYBwaONj6b2Ye1GiHfwjqyROoF4RwYO+vPwFk=
 github.com/spf13/pflag v1.0.10/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
 github.com/x448/float16 v0.8.4 h1:qLwI1I70+NjRFUR3zs1JPUCgaCXSh3SW62uAKT1mSBM=
 github.com/x448/float16 v0.8.4/go.mod h1:14CWIYCyZA/cWjXOioeEpHeN/83MdbZDRQHoFcYsOfg=
+golang.org/x/text v0.42.0 h1:JbOZXgfeCPU9gacVtYliJqOhD+zhrEqK4LfdpmlUZqI=
+golang.org/x/text v0.42.0/go.mod h1:ojzP1Z+2QtioaF8DTtO8K5q7JWVVYwZKenzujK0Zd0E=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
diff --git a/gp-module/internal/i18n/ids.go b/gp-module/internal/i18n/ids.go
new file mode 100644
index 000000000..7d6c1d4c8
--- /dev/null
+++ b/gp-module/internal/i18n/ids.go
@@ -0,0 +1,81 @@
+// Package i18n extracts the translatable message ids of a module directory.
+// The derivation itself lives in the shared i18n/modlocale package so the
+// operator applies exactly the same id set at install time.
+package i18n
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+
+	"github.com/GameplanePanel/gameplane/i18n/modlocale"
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+	"gopkg.in/yaml.v3"
+)
+
+// DefaultOutput is where Extract's result is written, relative to the module.
+const DefaultOutput = "locales/en.json"
+
+// Extract derives the English reference pack of the module in dir and returns
+// it as en.json content, descriptions included.
+func Extract(dir string) ([]byte, error) {
+	ref, err := reference(dir)
+	if err != nil {
+		return nil, err
+	}
+	data, err := pack.Marshal(ref)
+	if err != nil {
+		return nil, fmt.Errorf("encode reference pack: %w", err)
+	}
+	return data, nil
+}
+
+// reference derives the English reference pack of the module in dir. The
+// reference carries no sourceHash: only translations record one.
+func reference(dir string) (map[string]pack.Entry, error) {
+	module, err := readYAML(filepath.Join(dir, "module.yaml"), true)
+	if err != nil {
+		return nil, err
+	}
+	template, err := readYAML(filepath.Join(dir, "template.yaml"), true)
+	if err != nil {
+		return nil, err
+	}
+	return modlocale.References(modlocale.Derive(module, template)), nil
+}
+
+// WriteExtract runs Extract and writes the result to output, creating its
+// directory. An empty output means DefaultOutput inside dir.
+func WriteExtract(dir, output string) (string, error) {
+	data, err := Extract(dir)
+	if err != nil {
+		return "", err
+	}
+	if output == "" {
+		output = filepath.Join(dir, DefaultOutput)
+	}
+	if err := os.MkdirAll(filepath.Dir(output), 0o750); err != nil {
+		return "", fmt.Errorf("create output directory: %w", err)
+	}
+	if err := os.WriteFile(output, data, 0o600); err != nil {
+		return "", fmt.Errorf("write %s: %w", output, err)
+	}
+	return output, nil
+}
+
+func readYAML(path string, required bool) (map[string]any, error) {
+	data, err := os.ReadFile(filepath.Clean(path))
+	if err != nil {
+		if !required && errors.Is(err, fs.ErrNotExist) {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("read %s: %w", filepath.Base(path), err)
+	}
+	var out map[string]any
+	if err := yaml.Unmarshal(data, &out); err != nil {
+		return nil, fmt.Errorf("parse %s: %w", filepath.Base(path), err)
+	}
+	return out, nil
+}
diff --git a/gp-module/internal/i18n/ids_test.go b/gp-module/internal/i18n/ids_test.go
new file mode 100644
index 000000000..b420bbe15
--- /dev/null
+++ b/gp-module/internal/i18n/ids_test.go
@@ -0,0 +1,102 @@
+package i18n
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+)
+
+func writeModule(t *testing.T, module, template string) string {
+	t.Helper()
+	dir := t.TempDir()
+	if module != "" {
+		if err := os.WriteFile(filepath.Join(dir, "module.yaml"), []byte(module), 0o600); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if template != "" {
+		if err := os.WriteFile(filepath.Join(dir, "template.yaml"), []byte(template), 0o600); err != nil {
+			t.Fatal(err)
+		}
+	}
+	return dir
+}
+
+const (
+	testModule   = "name: demo\ndisplayName: Demo\nsummary: Runs {Demo}\n"
+	testTemplate = "spec:\n  displayName: Demo Game\n  configSchema:\n    - name: EULA\n      displayName: Accept EULA\n"
+)
+
+func TestExtract(t *testing.T) {
+	t.Parallel()
+	data, err := Extract(writeModule(t, testModule, testTemplate))
+	if err != nil {
+		t.Fatal(err)
+	}
+	ref, err := pack.ParseEntries(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, id := range []string{"module.displayName", "module.summary", "template.displayName", "config.EULA.displayName"} {
+		e, ok := ref[id]
+		if !ok || e.Description == "" {
+			t.Errorf("missing %s or description (%+v)", id, e)
+		}
+	}
+	if fs := pack.ValidateReference(ref, "en.json"); len(fs) != 0 {
+		t.Errorf("reference invalid: %v", fs)
+	}
+}
+
+func TestExtractErrors(t *testing.T) {
+	t.Parallel()
+	if _, err := Extract(writeModule(t, "", testTemplate)); err == nil || !strings.Contains(err.Error(), "module.yaml") {
+		t.Errorf("missing module.yaml: %v", err)
+	}
+	if _, err := Extract(writeModule(t, testModule, "")); err == nil || !strings.Contains(err.Error(), "template.yaml") {
+		t.Errorf("missing template.yaml: %v", err)
+	}
+	if _, err := Extract(writeModule(t, "name: [broken", testTemplate)); err == nil || !strings.Contains(err.Error(), "parse module.yaml") {
+		t.Errorf("bad module.yaml: %v", err)
+	}
+}
+
+func TestWriteExtractDefaultAndCustomOutput(t *testing.T) {
+	t.Parallel()
+	dir := writeModule(t, testModule, testTemplate)
+	got, err := WriteExtract(dir, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != filepath.Join(dir, "locales", "en.json") {
+		t.Errorf("default output = %s", got)
+	}
+	if _, err := os.Stat(got); err != nil {
+		t.Error(err)
+	}
+	custom := filepath.Join(t.TempDir(), "out", "ref.json")
+	if _, err := WriteExtract(dir, custom); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Stat(custom); err != nil {
+		t.Error(err)
+	}
+}
+
+func TestWriteExtractPropagatesError(t *testing.T) {
+	t.Parallel()
+	if _, err := WriteExtract(t.TempDir(), ""); err == nil {
+		t.Fatal("expected an error for an empty directory")
+	}
+}
+
+func TestReadYAMLOptional(t *testing.T) {
+	t.Parallel()
+	got, err := readYAML(filepath.Join(t.TempDir(), "absent.yaml"), false)
+	if err != nil || got != nil {
+		t.Fatalf("got %v, %v", got, err)
+	}
+}
diff --git a/gp-module/internal/i18n/stamp.go b/gp-module/internal/i18n/stamp.go
new file mode 100644
index 000000000..4dd76c0e5
--- /dev/null
+++ b/gp-module/internal/i18n/stamp.go
@@ -0,0 +1,82 @@
+package i18n
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+)
+
+// Stamp records the current English source hash (sourceHash, as in app packs)
+// on every translated entry of the module's locales/<tag>.json files that does
+// not have one yet. The English reference en.json is left alone. It returns the
+// files it rewrote, sorted. A file that does not parse is an error and nothing
+// after it is touched.
+func Stamp(dir string) ([]string, error) {
+	ref, err := reference(dir)
+	if err != nil {
+		return nil, err
+	}
+	localesDir := filepath.Join(dir, "locales")
+	entries, err := os.ReadDir(localesDir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("read locales directory: %w", err)
+	}
+	var stamped []string
+	for _, e := range entries {
+		name := e.Name()
+		if e.IsDir() || !e.Type().IsRegular() || !strings.HasSuffix(name, ".json") {
+			continue
+		}
+		tag := strings.TrimSuffix(name, ".json")
+		if tag == "en" {
+			continue
+		}
+		if !pack.ValidTag(tag) {
+			return stamped, fmt.Errorf("locales/%s: %q is not a valid language tag", name, tag)
+		}
+		path := filepath.Join(localesDir, name)
+		data, err := os.ReadFile(filepath.Clean(path))
+		if err != nil {
+			return stamped, fmt.Errorf("read locales/%s: %w", name, err)
+		}
+		tr, err := pack.ParseEntries(data)
+		if err != nil {
+			return stamped, fmt.Errorf("locales/%s: %w", name, err)
+		}
+		out, changed := pack.Stamp(ref, tr)
+		if !changed {
+			continue
+		}
+		encoded, err := pack.Marshal(out)
+		if err != nil {
+			return stamped, fmt.Errorf("encode locales/%s: %w", name, err)
+		}
+		if err := writeInDir(localesDir, name, encoded); err != nil {
+			return stamped, fmt.Errorf("write locales/%s: %w", name, err)
+		}
+		stamped = append(stamped, path)
+	}
+	sort.Strings(stamped)
+	return stamped, nil
+}
+
+// writeInDir writes name inside dir through an os.Root, so the write cannot
+// escape dir whatever the directory listing contained.
+func writeInDir(dir, name string, data []byte) error {
+	root, err := os.OpenRoot(dir)
+	if err != nil {
+		return fmt.Errorf("open %s: %w", dir, err)
+	}
+	defer func() { _ = root.Close() }()
+	if err := root.WriteFile(name, data, 0o600); err != nil {
+		return fmt.Errorf("write %s: %w", name, err)
+	}
+	return nil
+}
diff --git a/gp-module/internal/i18n/stamp_test.go b/gp-module/internal/i18n/stamp_test.go
new file mode 100644
index 000000000..69d882fb4
--- /dev/null
+++ b/gp-module/internal/i18n/stamp_test.go
@@ -0,0 +1,73 @@
+package i18n
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+)
+
+func TestStampRecordsSourceHash(t *testing.T) {
+	t.Parallel()
+	dir := writeModule(t, testModule, testTemplate)
+	if err := os.MkdirAll(filepath.Join(dir, "locales"), 0o750); err != nil {
+		t.Fatal(err)
+	}
+	fr := filepath.Join(dir, "locales", "fr.json")
+	en := filepath.Join(dir, "locales", "en.json")
+	if err := os.WriteFile(fr, []byte(`{"template.displayName":{"defaultMessage":"Jeu"}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(en, []byte(`{}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	stamped, err := Stamp(dir)
+	if err != nil || len(stamped) != 1 {
+		t.Fatalf("Stamp = %v, %v", stamped, err)
+	}
+	data, err := os.ReadFile(fr)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err := pack.ParseEntries(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got["template.displayName"].SourceHash != pack.SourceHash("Demo Game") {
+		t.Errorf("entry = %+v", got["template.displayName"])
+	}
+	if b, _ := os.ReadFile(en); string(b) != `{}` {
+		t.Errorf("en.json was rewritten: %q", b)
+	}
+
+	again, err := Stamp(dir)
+	if err != nil || len(again) != 0 {
+		t.Fatalf("second Stamp = %v, %v; want a no-op", again, err)
+	}
+}
+
+func TestStampWithoutLocalesIsNoOp(t *testing.T) {
+	t.Parallel()
+	stamped, err := Stamp(writeModule(t, testModule, testTemplate))
+	if err != nil || len(stamped) != 0 {
+		t.Fatalf("Stamp = %v, %v", stamped, err)
+	}
+}
+
+func TestStampRejectsBadFiles(t *testing.T) {
+	t.Parallel()
+	for name, body := range map[string]string{"xx_YY.json": `{}`, "fr.json": `[`} {
+		dir := writeModule(t, testModule, testTemplate)
+		if err := os.MkdirAll(filepath.Join(dir, "locales"), 0o750); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(filepath.Join(dir, "locales", name), []byte(body), 0o600); err != nil {
+			t.Fatal(err)
+		}
+		if _, err := Stamp(dir); err == nil {
+			t.Errorf("%s: expected an error", name)
+		}
+	}
+}
diff --git a/gp-module/internal/packager/archive_locales_test.go b/gp-module/internal/packager/archive_locales_test.go
new file mode 100644
index 000000000..563026404
--- /dev/null
+++ b/gp-module/internal/packager/archive_locales_test.go
@@ -0,0 +1,75 @@
+package packager
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"errors"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func archiveNames(t *testing.T, data []byte) []string {
+	t.Helper()
+	gz, err := gzip.NewReader(bytes.NewReader(data))
+	if err != nil {
+		t.Fatal(err)
+	}
+	tr := tar.NewReader(gz)
+	var names []string
+	for {
+		hdr, err := tr.Next()
+		if errors.Is(err, io.EOF) {
+			return names
+		}
+		if err != nil {
+			t.Fatal(err)
+		}
+		names = append(names, hdr.Name)
+	}
+}
+
+func writeModuleBase(t *testing.T, dir string) {
+	t.Helper()
+	for name, body := range map[string]string{"module.yaml": "name: demo\n", "template.yaml": "spec: {}\n", "README.md": "# demo\n"} {
+		if err := os.WriteFile(filepath.Join(dir, name), []byte(body), 0o600); err != nil {
+			t.Fatal(err)
+		}
+	}
+}
+
+func TestCreateArchiveFromDirCarriesLocales(t *testing.T) {
+	t.Parallel()
+	dir := t.TempDir()
+	writeModuleBase(t, dir)
+	writeLocale(t, dir, "fr.json", `{"a":1}`)
+	writeLocale(t, dir, "en.json", `{}`)
+	writeLocale(t, dir, "de.json", `{}`)
+
+	data, _, err := CreateArchiveFromDir(dir, PackageLimits{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	names := archiveNames(t, data)
+	want := []string{"module.yaml", "template.yaml", "README.md", "locales/de.json", "locales/fr.json"}
+	if len(names) != len(want) {
+		t.Fatalf("entries = %v, want %v", names, want)
+	}
+	for i := range want {
+		if names[i] != want[i] {
+			t.Fatalf("entries = %v, want %v", names, want)
+		}
+	}
+}
+
+func TestCreateArchiveFromDirRejectsInvalidLocaleTag(t *testing.T) {
+	t.Parallel()
+	dir := t.TempDir()
+	writeModuleBase(t, dir)
+	writeLocale(t, dir, "xx_YY.json", `{}`)
+	if _, _, err := CreateArchiveFromDir(dir, PackageLimits{}); err == nil {
+		t.Fatal("invalid language tag accepted")
+	}
+}
diff --git a/gp-module/internal/packager/locales_test.go b/gp-module/internal/packager/locales_test.go
new file mode 100644
index 000000000..2469a81bc
--- /dev/null
+++ b/gp-module/internal/packager/locales_test.go
@@ -0,0 +1,81 @@
+package packager
+
+import (
+	"os"
+	"path/filepath"
+	"reflect"
+	"testing"
+)
+
+func writeLocale(t *testing.T, dir, name, body string) {
+	t.Helper()
+	if err := os.MkdirAll(filepath.Join(dir, "locales"), 0o750); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(dir, "locales", name), []byte(body), 0o600); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestReadLocaleFilesMissingDir(t *testing.T) {
+	t.Parallel()
+	got, err := ReadLocaleFiles(t.TempDir())
+	if err != nil || len(got) != 0 {
+		t.Fatalf("got %v, %v", got, err)
+	}
+}
+
+func TestReadLocaleFilesSkipsEnglishAndNonJSON(t *testing.T) {
+	t.Parallel()
+	dir := t.TempDir()
+	writeLocale(t, dir, "en.json", "{}")
+	writeLocale(t, dir, "fr.json", `{"a":1}`)
+	writeLocale(t, dir, "pt-BR.json", "{}")
+	writeLocale(t, dir, "README.txt", "x")
+	if err := os.MkdirAll(filepath.Join(dir, "locales", "sub.json"), 0o750); err != nil {
+		t.Fatal(err)
+	}
+	got, err := ReadLocaleFiles(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(got) != 2 || string(got["locales/fr.json"]) != `{"a":1}` || got["locales/pt-BR.json"] == nil {
+		t.Fatalf("got %v", got)
+	}
+}
+
+func TestReadLocaleFilesRejectsSymlink(t *testing.T) {
+	t.Parallel()
+	dir := t.TempDir()
+	writeLocale(t, dir, "real.txt", "{}")
+	if err := os.Symlink(filepath.Join(dir, "locales", "real.txt"), filepath.Join(dir, "locales", "fr.json")); err != nil {
+		t.Skipf("symlinks unavailable: %v", err)
+	}
+	if _, err := ReadLocaleFiles(dir); err == nil {
+		t.Fatal("expected an error for a symlinked locale file")
+	}
+}
+
+func TestReadLocaleFilesRejectsBadTag(t *testing.T) {
+	t.Parallel()
+	dir := t.TempDir()
+	writeLocale(t, dir, "French.json", "{}")
+	if _, err := ReadLocaleFiles(dir); err == nil {
+		t.Fatal("expected an error for an invalid language tag")
+	}
+}
+
+func TestLocaleLayerArgs(t *testing.T) {
+	t.Parallel()
+	if got := localeLayerArgs(nil); len(got) != 0 {
+		t.Fatalf("got %v", got)
+	}
+	got := localeLayerArgs(map[string][]byte{"locales/fr.json": nil, "locales/de.json": nil})
+	want := []string{
+		"locales/de.json:" + MediaLocale,
+		"locales/fr.json:" + MediaLocale,
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("got %v want %v", got, want)
+	}
+}
diff --git a/gp-module/internal/packager/packager.go b/gp-module/internal/packager/packager.go
index ae1e7c428..f2d90f404 100644
--- a/gp-module/internal/packager/packager.go
+++ b/gp-module/internal/packager/packager.go
@@ -10,8 +10,10 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"sort"
 	"strings"
 
+	"github.com/GameplanePanel/gameplane/i18n/pack"
 	"gopkg.in/yaml.v3"
 )
 
@@ -22,6 +24,7 @@ const (
 	MediaTemplate = "application/vnd.gameplane.module.template.v1+yaml"
 	MediaReadme   = "application/vnd.gameplane.module.readme.v1+md"
 	MediaIcon     = "image/png"
+	MediaLocale   = "application/vnd.gameplane.module.locale.v1+json"
 
 	DefaultMaxIconSize   = 512 * 1024  // 512 KiB
 	DefaultMaxBundleSize = 1024 * 1024 // 1 MiB
@@ -143,11 +146,17 @@ func CreateArchiveFromFiles(files map[string][]byte, limits PackageLimits) ([]by
 		}
 	}
 
-	for name, data := range files {
+	// Remaining files go out in sorted order so the archive is reproducible.
+	rest := make([]string, 0, len(files))
+	for name := range files {
 		if !written[name] {
-			if err := writeFile(name, data); err != nil {
-				return nil, nil, fmt.Errorf("failed to write %s to tar: %w", name, err)
-			}
+			rest = append(rest, name)
+		}
+	}
+	sort.Strings(rest)
+	for _, name := range rest {
+		if err := writeFile(name, files[name]); err != nil {
+			return nil, nil, fmt.Errorf("failed to write %s to tar: %w", name, err)
 		}
 	}
 
@@ -167,6 +176,15 @@ func CreateArchiveFromDir(dirPath string, limits PackageLimits) ([]byte, []Packa
 	if err != nil {
 		return nil, nil, err
 	}
+	// Translations travel in the archive at the same relative path an OCI
+	// bundle uses as layer title: locales/<tag>.json (en.json is not shipped).
+	locales, err := ReadLocaleFiles(dirPath)
+	if err != nil {
+		return nil, nil, err
+	}
+	for name, data := range locales {
+		files[name] = data
+	}
 	return CreateArchiveFromFiles(files, limits)
 }
 
@@ -223,6 +241,62 @@ func ReadModuleFiles(dirPath string) (map[string][]byte, error) {
 	return files, nil
 }
 
+// ReadLocaleFiles reads the translation files of a module directory. Keys are
+// "locales/<tag>.json"; the English reference en.json is not shipped, and
+// non-JSON files are ignored. A missing locales directory yields an empty map.
+// Symbolic links and files whose name is not a valid language tag are errors.
+func ReadLocaleFiles(dirPath string) (map[string][]byte, error) {
+	dir := filepath.Join(dirPath, "locales")
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return map[string][]byte{}, nil
+		}
+		return nil, fmt.Errorf("failed to read locales directory %s: %w", dir, err)
+	}
+	out := make(map[string][]byte)
+	for _, entry := range entries {
+		name := entry.Name()
+		if entry.IsDir() || !strings.HasSuffix(name, ".json") {
+			continue
+		}
+		if entry.Type()&os.ModeSymlink != 0 {
+			return nil, fmt.Errorf("symbolic link not allowed in locales directory: %s", name)
+		}
+		if !entry.Type().IsRegular() {
+			continue
+		}
+		tag := strings.TrimSuffix(name, ".json")
+		if tag == "en" {
+			continue
+		}
+		if !pack.ValidTag(tag) {
+			return nil, fmt.Errorf("locales/%s: %q is not a valid language tag", name, tag)
+		}
+		data, err := os.ReadFile(filepath.Clean(filepath.Join(dir, name)))
+		if err != nil {
+			return nil, fmt.Errorf("failed to read locales/%s: %w", name, err)
+		}
+		out["locales/"+name] = data
+	}
+	return out, nil
+}
+
+// localeLayerArgs returns the oras layer arguments for locale files in a
+// deterministic (sorted) order. Each layer is titled with its relative path.
+func localeLayerArgs(locales map[string][]byte) []string {
+	names := make([]string, 0, len(locales))
+	for name := range locales {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+	args := make([]string, 0, len(names))
+	for _, name := range names {
+		args = append(args, fmt.Sprintf("%s:%s", name, MediaLocale))
+	}
+	return args
+}
+
 // PushOCI packages and pushes a module directory to an OCI registry using ORAS.
 func PushOCI(opts PackageOptions) ([]PackageWarning, error) {
 	files, err := ReadModuleFiles(opts.ModuleDir)
@@ -238,9 +312,17 @@ func PushOCI(opts PackageOptions) ([]PackageWarning, error) {
 		}
 	}
 
+	locales, err := ReadLocaleFiles(opts.ModuleDir)
+	if err != nil {
+		return nil, err
+	}
+
 	// Size checks
 	var warnings []PackageWarning
 	var totalSize int64
+	for _, content := range locales {
+		totalSize += int64(len(content))
+	}
 	for name, content := range files {
 		size := int64(len(content))
 		totalSize += size
@@ -304,6 +386,7 @@ func PushOCI(opts PackageOptions) ([]PackageWarning, error) {
 	if _, ok := files["icon.png"]; ok {
 		layerArgs = append(layerArgs, fmt.Sprintf("icon.png:%s", MediaIcon))
 	}
+	layerArgs = append(layerArgs, localeLayerArgs(locales)...)
 	cmdArgs = append(cmdArgs, layerArgs...)
 
 	cmd := exec.CommandContext(context.Background(), "oras", cmdArgs...)
diff --git a/gp-module/internal/validator/locales.go b/gp-module/internal/validator/locales.go
new file mode 100644
index 000000000..2798c69ea
--- /dev/null
+++ b/gp-module/internal/validator/locales.go
@@ -0,0 +1,163 @@
+package validator
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/GameplanePanel/gameplane/i18n/modlocale"
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+	"gopkg.in/yaml.v3"
+)
+
+const (
+	localesDir    = "locales/"
+	localesSuffix = ".json"
+	englishLocale = "en"
+)
+
+// localeTag returns the language tag of a "locales/<tag>.json" file name.
+func localeTag(name string) (string, bool) {
+	if !strings.HasPrefix(name, localesDir) || !strings.HasSuffix(name, localesSuffix) {
+		return "", false
+	}
+	tag := strings.TrimSuffix(strings.TrimPrefix(name, localesDir), localesSuffix)
+	if tag == "" || strings.Contains(tag, "/") {
+		return "", false
+	}
+	return tag, true
+}
+
+// validateLocales checks every locales/<tag>.json translation against the
+// English reference derived from module.yaml and template.yaml. Modules
+// without a locales directory are unaffected.
+func validateLocales(files map[string][]byte) []Finding {
+	var names []string
+	for name := range files {
+		if _, ok := localeTag(name); ok {
+			names = append(names, name)
+		}
+	}
+	if len(names) == 0 {
+		return nil
+	}
+	sort.Strings(names)
+
+	ref, ok := localeReference(files)
+	var findings []Finding
+	for _, name := range names {
+		tag, _ := localeTag(name)
+		if tag == englishLocale {
+			continue
+		}
+		if !pack.ValidTag(tag) {
+			findings = append(findings, localeFinding(name, "", fmt.Sprintf("%q is not a valid language tag", tag),
+				"Name the file after a BCP 47 tag such as fr.json, pt-BR.json or zh-Hans.json."))
+			continue
+		}
+		tr, err := pack.ParseEntries(files[name])
+		if err != nil {
+			findings = append(findings, localeFinding(name, "", fmt.Sprintf("translation file is malformed: %v", err),
+				"Make the file a JSON object mapping message ids to {\"defaultMessage\": \"...\"}."))
+			continue
+		}
+		if !ok {
+			continue
+		}
+		for _, f := range pack.ValidateTranslation(ref, tr, name) {
+			if f.Code == pack.CodeNeedsReview {
+				findings = append(findings, Finding{
+					Level:       SeverityWarn,
+					RuleID:      RuleLocaleNeedsReview,
+					File:        name,
+					Field:       f.ID,
+					Message:     "English text changed since this was translated; please review",
+					Remediation: "Review the translation, then run 'gp-module i18n stamp' to record the current English text.",
+				})
+				continue
+			}
+			if f.Severity != pack.SeverityError {
+				continue
+			}
+			findings = append(findings, localeFinding(name, f.ID, fmt.Sprintf("[%s] %s", f.Code, f.Message),
+				"Fix or remove the entry; invalid entries are dropped when the module is installed."))
+		}
+	}
+	return findings
+}
+
+// localeReference derives the English reference pack from the manifests, or
+// falls back to locales/en.json when the manifests derive nothing. ok is false
+// when no reference is available.
+func localeReference(files map[string][]byte) (map[string]pack.Entry, bool) {
+	if refs := deriveLocaleRefs(files); len(refs) > 0 {
+		return modlocale.References(refs), true
+	}
+	if data, found := files[localesDir+englishLocale+localesSuffix]; found {
+		if ref, err := pack.ParseEntries(data); err == nil {
+			return ref, true
+		}
+	}
+	return nil, false
+}
+
+// deriveLocaleRefs parses module.yaml and template.yaml the way localeReference
+// does and returns the translatable ids derived from them. A manifest that
+// fails to parse contributes nothing.
+func deriveLocaleRefs(files map[string][]byte) []modlocale.Ref {
+	var module, template map[string]any
+	if data, found := files["module.yaml"]; found {
+		if err := yaml.Unmarshal(data, &module); err != nil {
+			module = nil
+		}
+	}
+	if data, found := files["template.yaml"]; found {
+		if err := yaml.Unmarshal(data, &template); err != nil {
+			template = nil
+		}
+	}
+	return modlocale.Derive(module, template)
+}
+
+// validateLocaleIDs reports every derived translation id that the module id
+// rule rejects, because translators could not target such an id. It runs
+// whenever module.yaml or template.yaml is present, independent of locales/.
+func validateLocaleIDs(files map[string][]byte) []Finding {
+	_, hasModule := files["module.yaml"]
+	_, hasTemplate := files["template.yaml"]
+	if !hasModule && !hasTemplate {
+		return nil
+	}
+	var findings []Finding
+	for _, ref := range deriveLocaleRefs(files) {
+		if modlocale.ValidID(ref.ID) {
+			continue
+		}
+		file := "template.yaml"
+		if strings.HasPrefix(ref.ID, "module.") {
+			file = "module.yaml"
+		}
+		findings = append(findings, Finding{
+			Level:       SeverityError,
+			RuleID:      RuleLocaleIDInvalid,
+			File:        file,
+			Line:        0,
+			Field:       ref.ID,
+			Message:     fmt.Sprintf("%q cannot be used as a translation id: names may only use letters, digits, '_', '-' and '.'", ref.ID),
+			Remediation: "Rename the key or option value so it contains no spaces, '/', ':' or other symbols; translators cannot target it otherwise.",
+		})
+	}
+	return findings
+}
+
+func localeFinding(file, field, message, remediation string) Finding {
+	return Finding{
+		Level:       SeverityError,
+		RuleID:      RuleLocaleInvalid,
+		File:        file,
+		Line:        0,
+		Field:       field,
+		Message:     message,
+		Remediation: remediation,
+	}
+}
diff --git a/gp-module/internal/validator/locales_id_test.go b/gp-module/internal/validator/locales_id_test.go
new file mode 100644
index 000000000..925a81b13
--- /dev/null
+++ b/gp-module/internal/validator/locales_id_test.go
@@ -0,0 +1,53 @@
+package validator
+
+import (
+	"strings"
+	"testing"
+)
+
+func localeIDRuleFindings(fs []Finding) []Finding {
+	var out []Finding
+	for _, f := range fs {
+		if f.RuleID == RuleLocaleIDInvalid {
+			out = append(out, f)
+		}
+	}
+	return out
+}
+
+func TestValidateLocaleIDsSpacedConfigKey(t *testing.T) {
+	t.Parallel()
+	files := map[string][]byte{
+		"module.yaml":   []byte(localeModuleYAML),
+		"template.yaml": []byte("spec:\n  displayName: Demo Game\n  configSchema:\n    - name: MAX PLAYERS\n      displayName: Max players\n"),
+	}
+	got := validateLocaleIDs(files)
+	if len(got) != 1 {
+		t.Fatalf("findings = %v, want exactly one", got)
+	}
+	f := got[0]
+	if f.RuleID != RuleLocaleIDInvalid || f.Level != SeverityError || f.File != "template.yaml" {
+		t.Fatalf("finding = %+v", f)
+	}
+	const id = "config.MAX PLAYERS.displayName"
+	if f.Field != id || !strings.Contains(f.Message, `"`+id+`"`) {
+		t.Fatalf("finding does not name %q: %+v", id, f)
+	}
+	if f.Remediation == "" {
+		t.Error("finding has no remediation")
+	}
+}
+
+func TestValidateLocaleIDsCleanTemplate(t *testing.T) {
+	t.Parallel()
+	files := map[string][]byte{
+		"module.yaml":   []byte(localeModuleYAML),
+		"template.yaml": []byte("spec:\n  displayName: Demo Game\n  configSchema:\n    - name: MAX_PLAYERS\n      displayName: Max players\n      enum: [easy, hard]\n"),
+	}
+	if got := validateLocaleIDs(files); len(got) != 0 {
+		t.Fatalf("unexpected findings: %v", got)
+	}
+	if got := localeIDRuleFindings(validateLocales(files)); len(got) != 0 {
+		t.Fatalf("unexpected locale-id-invalid findings: %v", got)
+	}
+}
diff --git a/gp-module/internal/validator/locales_needs_review_test.go b/gp-module/internal/validator/locales_needs_review_test.go
new file mode 100644
index 000000000..936e164e1
--- /dev/null
+++ b/gp-module/internal/validator/locales_needs_review_test.go
@@ -0,0 +1,21 @@
+package validator
+
+import "testing"
+
+func TestValidateLocalesStaleHashIsWarning(t *testing.T) {
+	t.Parallel()
+	files := localeFiles(map[string]string{
+		"locales/fr.json": `{"template.displayName":{"defaultMessage":"Jeu","sourceHash":"000000000000"}}`,
+	})
+	got := validateLocales(files)
+	if len(got) != 1 {
+		t.Fatalf("findings = %v, want exactly one", got)
+	}
+	f := got[0]
+	if f.RuleID != RuleLocaleNeedsReview || f.Level != SeverityWarn || f.Field != "template.displayName" || f.File != "locales/fr.json" {
+		t.Fatalf("finding = %+v", f)
+	}
+	if len(localeRuleFindings(got)) != 0 {
+		t.Error("a stale hash must not be a locale-invalid error")
+	}
+}
diff --git a/gp-module/internal/validator/locales_test.go b/gp-module/internal/validator/locales_test.go
new file mode 100644
index 000000000..e6e457434
--- /dev/null
+++ b/gp-module/internal/validator/locales_test.go
@@ -0,0 +1,145 @@
+package validator
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const localeModuleYAML = "name: demo\ndisplayName: Demo\nsummary: A demo\nversion: 0.1.0\n"
+const localeTemplateYAML = "spec:\n  displayName: Demo Game\n"
+
+func localeFiles(extra map[string]string) map[string][]byte {
+	files := map[string][]byte{
+		"module.yaml":   []byte(localeModuleYAML),
+		"template.yaml": []byte(localeTemplateYAML),
+	}
+	for k, v := range extra {
+		files[k] = []byte(v)
+	}
+	return files
+}
+
+func localeRuleFindings(fs []Finding) []Finding {
+	var out []Finding
+	for _, f := range fs {
+		if f.RuleID == RuleLocaleInvalid {
+			out = append(out, f)
+		}
+	}
+	return out
+}
+
+func TestValidateLocalesNoneIsUnchanged(t *testing.T) {
+	t.Parallel()
+	if got := validateLocales(localeFiles(nil)); len(got) != 0 {
+		t.Fatalf("findings without locales: %v", got)
+	}
+}
+
+func TestValidateLocalesValid(t *testing.T) {
+	t.Parallel()
+	files := localeFiles(map[string]string{
+		"locales/fr.json":    `{"module.displayName":{"defaultMessage":"Démo"},"template.displayName":{"defaultMessage":"Jeu"}}`,
+		"locales/pt-BR.json": `{"module.summary":{"defaultMessage":"Uma demo"}}`,
+		"locales/en.json":    `{"module.displayName":{"defaultMessage":"Demo","description":"d"}}`,
+	})
+	if got := validateLocales(files); len(got) != 0 {
+		t.Fatalf("unexpected findings: %v", got)
+	}
+}
+
+func TestValidateLocalesBadPlaceholderAndUnknownID(t *testing.T) {
+	t.Parallel()
+	files := localeFiles(map[string]string{
+		"locales/fr.json": `{"module.displayName":{"defaultMessage":"{x}"},"nope":{"defaultMessage":"y"}}`,
+	})
+	got := validateLocales(files)
+	if len(got) != 2 {
+		t.Fatalf("want 2 findings, got %v", got)
+	}
+	var text strings.Builder
+	for _, f := range got {
+		if f.Level != SeverityError || f.RuleID != RuleLocaleInvalid || f.File != "locales/fr.json" || f.Remediation == "" {
+			t.Errorf("bad finding %+v", f)
+		}
+		text.WriteString(f.Field + " " + f.Message + "\n")
+	}
+	for _, want := range []string{"module.displayName", "extra-placeholder", "nope", "unknown-id"} {
+		if !strings.Contains(text.String(), want) {
+			t.Errorf("findings do not mention %q:\n%s", want, text.String())
+		}
+	}
+}
+
+func TestValidateLocalesBadTagAndMalformed(t *testing.T) {
+	t.Parallel()
+	files := localeFiles(map[string]string{
+		"locales/FR_fr.json":      `{}`,
+		"locales/de.json":         `{not json`,
+		"locales/nested/x/y.json": `{}`,
+	})
+	got := validateLocales(files)
+	if len(got) != 2 {
+		t.Fatalf("want 2 findings, got %v", got)
+	}
+	if !strings.Contains(got[0].Message, "not a valid language tag") && !strings.Contains(got[1].Message, "not a valid language tag") {
+		t.Errorf("missing tag finding: %v", got)
+	}
+	if !strings.Contains(got[0].Message+got[1].Message, "malformed") {
+		t.Errorf("missing malformed finding: %v", got)
+	}
+}
+
+func TestValidateLocalesFallsBackToEnglishFile(t *testing.T) {
+	t.Parallel()
+	files := map[string][]byte{
+		"module.yaml":     []byte("name: demo\n"),
+		"template.yaml":   []byte("spec: {}\n"),
+		"locales/en.json": []byte(`{"custom":{"defaultMessage":"Hi {name}","description":"d"}}`),
+		"locales/fr.json": []byte(`{"custom":{"defaultMessage":"Salut"}}`),
+	}
+	got := validateLocales(files)
+	if len(got) != 1 || !strings.Contains(got[0].Message, "missing-placeholder") {
+		t.Fatalf("got %v", got)
+	}
+}
+
+func TestValidateLocalesNoReferenceSkipsContentChecks(t *testing.T) {
+	t.Parallel()
+	files := map[string][]byte{
+		"module.yaml":     []byte("name: [broken"),
+		"template.yaml":   []byte("spec: [broken"),
+		"locales/fr.json": []byte(`{"a":{"defaultMessage":"x"}}`),
+	}
+	if got := validateLocales(files); len(got) != 0 {
+		t.Fatalf("got %v", got)
+	}
+}
+
+func TestValidateDirectoryReadsLocales(t *testing.T) {
+	t.Parallel()
+	dir := filepath.Join(t.TempDir(), "demo")
+	if err := os.MkdirAll(filepath.Join(dir, "locales"), 0o750); err != nil {
+		t.Fatal(err)
+	}
+	write := func(name, body string) {
+		if err := os.WriteFile(filepath.Join(dir, name), []byte(body), 0o600); err != nil {
+			t.Fatal(err)
+		}
+	}
+	write("module.yaml", localeModuleYAML)
+	write("template.yaml", localeTemplateYAML)
+	write("README.md", "# demo\n")
+	write("locales/fr.json", `{"module.displayName":{"defaultMessage":"{x}"}}`)
+	write("locales/notes.txt", "ignored")
+	rep, err := ValidateDirectory(dir, ValidateOptions{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := localeRuleFindings(rep.Findings)
+	if len(got) != 1 || got[0].File != "locales/fr.json" {
+		t.Fatalf("locale findings = %v", got)
+	}
+}
diff --git a/gp-module/internal/validator/report.go b/gp-module/internal/validator/report.go
index 3531d29a9..fb148fe85 100644
--- a/gp-module/internal/validator/report.go
+++ b/gp-module/internal/validator/report.go
@@ -33,6 +33,9 @@ const (
 	RuleInsecureAuthField       = "credential-field-not-password"
 	RuleExcessiveAssetSize      = "excessive-asset-size"
 	RuleMinVersionExceedsTool   = "gameplane-min-version-exceeds-tool"
+	RuleLocaleInvalid           = "locale-invalid"
+	RuleLocaleIDInvalid         = "locale-id-invalid"
+	RuleLocaleNeedsReview       = "locale-needs-review"
 )
 
 // ToolVersion is the gp-module release. cmd/gp-module surfaces it via
diff --git a/gp-module/internal/validator/validator.go b/gp-module/internal/validator/validator.go
index e10af6e4c..6cb8451aa 100644
--- a/gp-module/internal/validator/validator.go
+++ b/gp-module/internal/validator/validator.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/GameplanePanel/gameplane/gp-module/internal/common"
 )
@@ -41,6 +42,11 @@ func ValidateDirectory(dirPath string, opts ValidateOptions) (*ModuleReport, err
 
 	for _, entry := range entries {
 		if entry.IsDir() {
+			if entry.Name() == "locales" {
+				if err := readLocaleFiles(absPath, files); err != nil {
+					return nil, err
+				}
+			}
 			continue
 		}
 		path := filepath.Join(absPath, entry.Name())
@@ -71,6 +77,29 @@ func ValidateDirectory(dirPath string, opts ValidateOptions) (*ModuleReport, err
 	return report, nil
 }
 
+// readLocaleFiles adds every regular locales/*.json file of the module to
+// files under the key "locales/<name>". Symlinks and other entries are skipped.
+// They do not count towards the asset size checks.
+func readLocaleFiles(absPath string, files map[string][]byte) error {
+	dir := filepath.Join(absPath, "locales")
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		return fmt.Errorf("failed to read directory %q: %w", dir, err)
+	}
+	for _, entry := range entries {
+		if !entry.Type().IsRegular() || !strings.HasSuffix(entry.Name(), ".json") {
+			continue
+		}
+		path := filepath.Join(dir, entry.Name())
+		data, err := os.ReadFile(filepath.Clean(path))
+		if err != nil {
+			return fmt.Errorf("failed to read file %q: %w", path, err)
+		}
+		files["locales/"+entry.Name()] = data
+	}
+	return nil
+}
+
 // ValidateFiles executes all validation rules against an in-memory map of file contents.
 func ValidateFiles(dirName string, files map[string][]byte, opts ValidateOptions) (*ModuleReport, error) {
 	var findings []Finding
@@ -142,6 +171,9 @@ func ValidateFiles(dirName string, files map[string][]byte, opts ValidateOptions
 		}
 	}
 
+	findings = append(findings, validateLocales(files)...)
+	findings = append(findings, validateLocaleIDs(files)...)
+
 	repName := dirName
 	if repName == "" || repName == "." {
 		repName = moduleName
diff --git a/gp-module/specs.md b/gp-module/specs.md
index b5ff640c3..158aec390 100644
--- a/gp-module/specs.md
+++ b/gp-module/specs.md
@@ -10,7 +10,8 @@
 1. **Scaffolding (`init`)**: Interactive and non-interactive generation of schema-compliant module directories across `steamcmd`, `java`, and `generic` archetypes with DNS-1123 validation.
 2. **Offline Validation (`validate`)**: Static offline checking of `module.yaml` metadata, CRD schemas, image digest pinning, canonical categories, port bounds/collisions, and configuration rules with exact source line-number diagnostics via `yaml.v3`.
 3. **Dry-Run Preview (`preview`)**: Simulation of runtime server creation from `template.yaml`, evaluating dynamic memory limits (`autoFromMemoryLimit`) and environment variable precedence using native Kubernetes resource types.
-4. **OCI Packaging (`package`)**: Asset size sanity checking (icon $\le$ 512 KiB, bundle $\le$ 1 MiB) and automated bundle export via ORAS or local `.tar.gz` archive.
+4. **OCI Packaging (`package`)**: Asset size sanity checking (icon $\le$ 512 KiB, bundle $\le$ 1 MiB) and automated bundle export via ORAS or local `.tar.gz` archive. A `locales/<tag>.json` translation file becomes one extra OCI layer (media type `application/vnd.gameplane.module.locale.v1+json`, title `locales/<tag>.json`); the English reference `locales/en.json` is not shipped. The local `.tar.gz` export carries `locales/<tag>.json` at the same relative path (`en.json` excluded), so it also works as an HTTP or upload source.
+5. **Translations (`i18n extract`, `i18n stamp`, and `validate`)**: `gp-module i18n extract [MODULE_PATH] [--output <file>]` derives the translatable message ids from `module.yaml` and `template.yaml` (shared `i18n/modlocale` package, also used by the operator) and writes the English reference with translator descriptions to `locales/en.json`. `validate` checks every `locales/<tag>.json` against the derived ids and reports rule `locale-invalid` for bad tags, malformed files, unknown ids and placeholder or markup mismatches. Each id derived from `module.yaml` and `template.yaml` that fails `modlocale.ValidID` (for example a config key with a space) is reported as an `ERROR` with rule `locale-id-invalid`, whether or not a `locales/` directory exists. `gp-module i18n stamp [MODULE_PATH]` records `sourceHash` (as in app packs) on translated entries that lack one; when the English text later changes, `validate` reports a `WARN` with rule `locale-needs-review` (it does not fail validation).
 
 ## Responsibilities
 
@@ -40,7 +41,8 @@ gp-module/
 │       ├── init.go               # 'init' command flags and interactive prompts
 │       ├── validate.go           # 'validate' command flags and reporting
 │       ├── preview.go            # 'preview' command flags and formatting
-│       └── package.go            # 'package' command flags and packaging
+│       ├── package.go            # 'package' command flags and packaging
+│       └── i18n.go               # 'i18n extract' command
 ├── pkg/                          # Public Go API exported to api/ and other modules
 │   ├── archetypes/               # Archetypes and icon helpers
 │   ├── packager/                 # Archive creation and size limits
@@ -62,13 +64,17 @@ gp-module/
 │   │   ├── rules.go              # Lint rules implementation
 │   │   ├── schema.go             # Schema conformance verification
 │   │   ├── report.go             # Diagnostic formatter and JSON reporter
+│   │   ├── locales.go            # locales/<tag>.json validation (rule locale-invalid)
 │   │   └── validator_test.go     # Validator unit tests
+│   ├── i18n/
+│   │   ├── ids.go                # Extract: derive and write the English reference pack
+│   │   └── stamp.go              # Stamp: record sourceHash on translated entries
 │   ├── preview/
 │   │   ├── preview.go            # Manifest simulator and env merger
 │   │   ├── memory.go             # autoFromMemoryLimit calculator
 │   │   └── preview_test.go       # Preview unit tests
 │   └── packager/
-│       ├── packager.go           # OCI bundle packager and size checker
+│       ├── packager.go           # OCI bundle packager, size checker and locale layers
 │       └── packager_test.go      # Packager unit tests
 ├── go.mod                        # Go module declaration
 ├── specs.md                      # Architecture and boundaries specification
diff --git a/hack/auto_label.py b/hack/auto_label.py
index edabfbbf6..e2a138489 100755
--- a/hack/auto_label.py
+++ b/hack/auto_label.py
@@ -62,8 +62,12 @@
     "audit-syslog-bridge": "area: optional-components",
     "telemetry-receiver": "area: optional-components",
     "telemetryschema": "area: shared",
+    "i18n": "area: shared",
 }
 
+# Shared translation packs. A PR that changes only these files is `type: docs`.
+TRANSLATION_PREFIX = "i18n/locales/"
+
 AREA_BY_FILE = {
     "design.pen": "area: web",
     "docs/module-authoring.md": "area: modules",
@@ -96,12 +100,19 @@ def area_for_path(path):
 
 
 def planned_labels(title, files, existing):
-    """Labels to add to a PR, given its title, changed files and labels."""
+    """Labels to add to a PR, given its title, changed files and labels.
+
+    A PR whose title gives no type, and whose files all sit under
+    i18n/locales/, is a translation-only docs change, so it gets `type: docs`.
+    """
     existing = set(existing)
     add = []
     type_label, breaking = parse_title(title)
-    if type_label and not any(name.startswith("type: ") for name in existing):
-        add.append(type_label)
+    if not any(name.startswith("type: ") for name in existing):
+        if type_label:
+            add.append(type_label)
+        elif files and all(f.startswith(TRANSLATION_PREFIX) for f in files):
+            add.append("type: docs")
     if files and not any(name.startswith("area: ") for name in existing):
         areas = {area_for_path(f) for f in files} - {None}
         add.extend(sorted(areas) or ["area: shared"])
@@ -157,7 +168,10 @@ def main(argv):
         existing = [label["name"] for label in pr.get("labels", [])]
         try:
             files = []
-            if not any(name.startswith("area: ") for name in existing):
+            # Changed files decide the area and a translation-only docs type.
+            missing_area = not any(name.startswith("area: ") for name in existing)
+            missing_type = not any(name.startswith("type: ") for name in existing)
+            if missing_area or missing_type:
                 files = [
                     f["filename"]
                     for f in paginate(f"/repos/{repo}/pulls/{number}/files", token)
diff --git a/hack/test_auto_label.py b/hack/test_auto_label.py
index e28f8b941..e19d6cb84 100755
--- a/hack/test_auto_label.py
+++ b/hack/test_auto_label.py
@@ -99,6 +99,41 @@ def test_docs_only_count_alone(self):
     def test_unknown_prefix_still_gets_area(self):
         self.assertEqual(planned_labels("Update stuff", ["web/a.ts"], []), ["area: web"])
 
+    def test_translation_pack_gets_docs_and_shared(self):
+        files = ["i18n/locales/fr/app.json", "i18n/locales/fr/meta.json"]
+        self.assertEqual(
+            planned_labels("Add French pack", files, []),
+            ["type: docs", "area: shared"],
+        )
+
+    def test_translation_pack_keeps_title_type(self):
+        files = ["i18n/locales/fr/app.json", "i18n/locales/fr/meta.json"]
+        self.assertEqual(
+            planned_labels("feat(i18n): add French", files, []),
+            ["type: feature", "area: shared"],
+        )
+
+    def test_translation_pack_with_other_files_is_not_docs(self):
+        files = ["i18n/locales/fr/app.json", "web/a.ts"]
+        self.assertEqual(
+            planned_labels("Add French pack", files, []),
+            ["area: shared", "area: web"],
+        )
+
+    def test_translation_pack_existing_type_untouched(self):
+        files = ["i18n/locales/fr/app.json"]
+        self.assertEqual(
+            planned_labels("Add French pack", files, ["type: fix"]),
+            ["area: shared"],
+        )
+
+
+class TranslationPackAreas(unittest.TestCase):
+    def test_i18n_locales_is_shared(self):
+        for path in ("i18n/locales/fr/app.json", "i18n/locales/fr/meta.json"):
+            with self.subTest(path=path):
+                self.assertEqual(area_for_path(path), "area: shared")
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/i18n/.testcoverage.yml b/i18n/.testcoverage.yml
new file mode 100644
index 000000000..ce533f721
--- /dev/null
+++ b/i18n/.testcoverage.yml
@@ -0,0 +1,13 @@
+# Coverage threshold gate for the shared i18n module.
+# Enforced by `make cover-go-check` via go-test-coverage/v2.
+#
+# i18n holds the shared language packs, the ICU message formatter, the pack
+# validator and the i18n-check CLI. Almost all of it is pure and unit-testable,
+# so the gate is 90%.
+profile: coverage/unit.out
+github-action-output: false
+
+threshold:
+  file: 0
+  package: 0
+  total: 90
diff --git a/i18n/catalog/catalog.go b/i18n/catalog/catalog.go
new file mode 100644
index 000000000..c286ae549
--- /dev/null
+++ b/i18n/catalog/catalog.go
@@ -0,0 +1,244 @@
+// Package catalog loads the embedded language packs and resolves message ids
+// to formatted text at runtime.
+package catalog
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"path"
+	"slices"
+	"sync"
+
+	"golang.org/x/text/language"
+
+	"github.com/GameplanePanel/gameplane/i18n"
+	"github.com/GameplanePanel/gameplane/i18n/icu"
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+)
+
+// Catalog is an immutable set of validated language packs plus a cache of
+// parsed messages. It is safe for concurrent use.
+type Catalog struct {
+	reference    string
+	packs        map[string]map[string]pack.Entry // tag -> valid entries; reference included
+	meta         map[string]pack.Meta
+	completeness map[string]float64
+
+	mu    sync.RWMutex
+	cache map[cacheKey]icu.Message
+}
+
+type cacheKey struct{ tag, id string }
+
+type languagePack struct {
+	tag     string
+	entries map[string]pack.Entry
+	meta    pack.Meta
+}
+
+func newCatalog(reference string) *Catalog {
+	return &Catalog{
+		reference:    reference,
+		packs:        map[string]map[string]pack.Entry{},
+		meta:         map[string]pack.Meta{},
+		completeness: map[string]float64{},
+		cache:        map[cacheKey]icu.Message{},
+	}
+}
+
+// Load reads every language pack under the locales/ directory of fsys (pass
+// i18n.Locales in production). Every directory with an app.json is a language.
+// The reference pack must parse and may omit meta.json; other packs are skipped
+// when their app.json or meta.json is missing or invalid. Translations are
+// reduced to the entries pack.Valid keeps.
+func Load(fsys fs.FS, reference string) (*Catalog, error) {
+	dirs, err := fs.ReadDir(fsys, "locales")
+	if err != nil {
+		return nil, fmt.Errorf("catalog: read locales: %w", err)
+	}
+
+	var (
+		refEntries map[string]pack.Entry
+		refMeta    pack.Meta
+		others     []languagePack
+	)
+	for _, d := range dirs {
+		if !d.IsDir() {
+			continue
+		}
+		tag := d.Name()
+		entries, err := readEntries(fsys, tag)
+		meta, metaErr := readMeta(fsys, tag)
+		if tag == reference {
+			if err != nil {
+				return nil, fmt.Errorf("catalog: reference %q: %w", tag, err)
+			}
+			if metaErr != nil && !errors.Is(metaErr, fs.ErrNotExist) {
+				return nil, fmt.Errorf("catalog: reference %q meta: %w", tag, metaErr)
+			}
+			refEntries = entries
+			refMeta = pack.Meta{Tag: tag, Direction: "ltr"}
+			if metaErr == nil {
+				refMeta = meta
+			}
+			continue
+		}
+		if err != nil || metaErr != nil || meta.Tag != tag {
+			continue
+		}
+		others = append(others, languagePack{tag: tag, entries: entries, meta: meta})
+	}
+	if refEntries == nil {
+		return nil, fmt.Errorf("catalog: reference %q not found under locales/", reference)
+	}
+
+	c := newCatalog(reference)
+	c.packs[reference] = refEntries
+	c.meta[reference] = refMeta
+	c.completeness[reference] = 100
+	for _, p := range others {
+		c.packs[p.tag] = pack.Valid(refEntries, p.entries)
+		c.meta[p.tag] = p.meta
+		c.completeness[p.tag] = pack.Completeness(refEntries, p.entries)
+	}
+	return c, nil
+}
+
+func readEntries(fsys fs.FS, tag string) (map[string]pack.Entry, error) {
+	data, err := fs.ReadFile(fsys, path.Join("locales", tag, "app.json"))
+	if err != nil {
+		return nil, err
+	}
+	return pack.ParseEntries(data)
+}
+
+func readMeta(fsys fs.FS, tag string) (pack.Meta, error) {
+	data, err := fs.ReadFile(fsys, path.Join("locales", tag, "meta.json"))
+	if err != nil {
+		return pack.Meta{}, err
+	}
+	return pack.ParseMeta(data)
+}
+
+// defaultOnce guards the lazily loaded embedded catalog.
+var (
+	defaultOnce sync.Once
+	defaultCat  *Catalog
+)
+
+// Default returns the catalog built from the embedded packs in package i18n.
+// If the embedded packs cannot be loaded it returns an empty catalog, so every
+// Lookup reports false and callers fall back to their own text.
+func Default() *Catalog {
+	defaultOnce.Do(func() {
+		c, err := Load(i18n.Locales, "en")
+		if err != nil {
+			c = newCatalog("en")
+		}
+		defaultCat = c
+	})
+	return defaultCat
+}
+
+// Tags returns every loaded language tag, the reference first and the rest
+// sorted.
+func (c *Catalog) Tags() []string {
+	others := make([]string, 0, len(c.packs))
+	for tag := range c.packs {
+		if tag != c.reference {
+			others = append(others, tag)
+		}
+	}
+	slices.Sort(others)
+	if _, ok := c.packs[c.reference]; ok {
+		return append([]string{c.reference}, others...)
+	}
+	return others
+}
+
+// Listed returns the tags offered to users, in the order of Tags.
+func (c *Catalog) Listed() []string {
+	var out []string
+	for _, tag := range c.Tags() {
+		if c.IsListed(tag) {
+			out = append(out, tag)
+		}
+	}
+	return out
+}
+
+// IsListed reports whether tag is offered to users. The reference is always
+// listed.
+func (c *Catalog) IsListed(tag string) bool {
+	comp, ok := c.completeness[tag]
+	if !ok {
+		return false
+	}
+	if tag == c.reference {
+		return true
+	}
+	return pack.Listed(tag, c.meta[tag], comp)
+}
+
+// Completeness returns the percentage of reference messages that tag translates.
+func (c *Catalog) Completeness(tag string) (float64, bool) {
+	comp, ok := c.completeness[tag]
+	return comp, ok
+}
+
+// Lookup formats message id for tag. It tries the exact tag, then its base
+// language, then the reference. Entries that fail to parse fall through to the
+// next pack. ok is false only when the reference does not have id.
+func (c *Catalog) Lookup(tag language.Tag, id string, args map[string]any) (string, bool) {
+	base, _ := tag.Base()
+	keys := []string{tag.String(), base.String(), c.reference}
+	for i, key := range keys {
+		if slices.Contains(keys[:i], key) {
+			continue
+		}
+		entry, ok := c.packs[key][id]
+		if !ok {
+			continue
+		}
+		msg, err := c.parse(key, id, entry.DefaultMessage)
+		if err != nil {
+			continue
+		}
+		return icu.Format(msg, language.Make(key), args), true
+	}
+	return "", false
+}
+
+// parse returns the parsed message for key/id, caching successful parses.
+func (c *Catalog) parse(key, id, text string) (icu.Message, error) {
+	ck := cacheKey{tag: key, id: id}
+	c.mu.RLock()
+	msg, ok := c.cache[ck]
+	c.mu.RUnlock()
+	if ok {
+		return msg, nil
+	}
+	msg, err := icu.Parse(text)
+	if err != nil {
+		return nil, fmt.Errorf("catalog: parse %s/%s: %w", key, id, err)
+	}
+	c.mu.Lock()
+	c.cache[ck] = msg
+	c.mu.Unlock()
+	return msg, nil
+}
+
+// Tags returns the tags of the default catalog.
+func Tags() []string { return Default().Tags() }
+
+// Listed returns the listed tags of the default catalog.
+func Listed() []string { return Default().Listed() }
+
+// IsListed reports whether tag is listed in the default catalog.
+func IsListed(tag string) bool { return Default().IsListed(tag) }
+
+// Lookup formats message id using the default catalog.
+func Lookup(tag language.Tag, id string, args map[string]any) (string, bool) {
+	return Default().Lookup(tag, id, args)
+}
diff --git a/i18n/catalog/catalog_test.go b/i18n/catalog/catalog_test.go
new file mode 100644
index 000000000..c89a84d04
--- /dev/null
+++ b/i18n/catalog/catalog_test.go
@@ -0,0 +1,184 @@
+package catalog
+
+import (
+	"fmt"
+	"testing"
+	"testing/fstest"
+
+	"golang.org/x/text/language"
+
+	"github.com/GameplanePanel/gameplane/i18n"
+)
+
+func testFS(files map[string]string) fstest.MapFS {
+	fsys := fstest.MapFS{}
+	for name, body := range files {
+		fsys["locales/"+name] = &fstest.MapFile{Data: []byte(body)}
+	}
+	return fsys
+}
+
+func metaJSON(tag, direction string) string {
+	return fmt.Sprintf(`{"tag":%q,"nativeName":"N-%s","englishName":"E-%s","direction":%q}`, tag, tag, tag, direction)
+}
+
+func TestLookupFallbackChain(t *testing.T) {
+	c, err := Load(testFS(map[string]string{
+		"en/app.json":     `{"a":{"defaultMessage":"A"},"b":{"defaultMessage":"B"},"x":{"defaultMessage":"X"}}`,
+		"en/meta.json":    metaJSON("en", "ltr"),
+		"fr/app.json":     `{"a":{"defaultMessage":"Afr"},"x":{"defaultMessage":"Xfr"}}`,
+		"fr/meta.json":    metaJSON("fr", "ltr"),
+		"fr-CA/app.json":  `{"a":{"defaultMessage":"Afr-CA"}}`,
+		"fr-CA/meta.json": metaJSON("fr-CA", "ltr"),
+	}), "en")
+	if err != nil {
+		t.Fatal(err)
+	}
+	tests := []struct {
+		tag, id, want string
+	}{
+		{"fr-CA", "a", "Afr-CA"},
+		{"fr-CA", "x", "Xfr"},
+		{"fr-CA", "b", "B"},
+		{"fr", "b", "B"},
+		{"en-GB", "a", "A"},
+	}
+	for _, tc := range tests {
+		got, ok := c.Lookup(language.MustParse(tc.tag), tc.id, nil)
+		if !ok || got != tc.want {
+			t.Errorf("Lookup(%s, %s) = %q, %v; want %q", tc.tag, tc.id, got, ok, tc.want)
+		}
+	}
+}
+
+func TestInvalidTranslationDroppedForReference(t *testing.T) {
+	c, err := Load(testFS(map[string]string{
+		"en/app.json":  `{"n":{"defaultMessage":"{count} files"}}`,
+		"en/meta.json": metaJSON("en", "ltr"),
+		"fr/app.json":  `{"n":{"defaultMessage":"{n} fichiers"}}`,
+		"fr/meta.json": metaJSON("fr", "ltr"),
+	}), "en")
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, ok := c.Lookup(language.French, "n", map[string]any{"count": 2})
+	if !ok || got != "2 files" {
+		t.Errorf("Lookup = %q, %v; want %q, true", got, ok, "2 files")
+	}
+}
+
+func TestLookupMissingID(t *testing.T) {
+	c, err := Load(testFS(map[string]string{
+		"en/app.json": `{"a":{"defaultMessage":"A"}}`,
+	}), "en")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := c.Lookup(language.English, "nope", nil); ok {
+		t.Error("Lookup of an id the reference lacks reported ok")
+	}
+}
+
+func TestListedThreshold(t *testing.T) {
+	c, err := Load(testFS(map[string]string{
+		"en/app.json":  `{"a":{"defaultMessage":"A"},"b":{"defaultMessage":"B"}}`,
+		"en/meta.json": metaJSON("en", "ltr"),
+		"de/app.json":  `{"a":{"defaultMessage":"Ade"}}`,
+		"de/meta.json": metaJSON("de", "ltr"),
+		"fr/app.json":  `{"a":{"defaultMessage":"Afr"},"b":{"defaultMessage":"Bfr"}}`,
+		"fr/meta.json": metaJSON("fr", "ltr"),
+		"ar/app.json":  `{"a":{"defaultMessage":"Aar"},"b":{"defaultMessage":"Bar"}}`,
+		"ar/meta.json": metaJSON("ar", "rtl"),
+	}), "en")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := fmt.Sprint(c.Tags()); got != "[en ar de fr]" {
+		t.Errorf("Tags() = %s; want [en ar de fr]", got)
+	}
+	if got := fmt.Sprint(c.Listed()); got != "[en fr]" {
+		t.Errorf("Listed() = %s; want [en fr]", got)
+	}
+	if c.IsListed("de") {
+		t.Error("50% pack reported as listed")
+	}
+	if !c.IsListed("en") {
+		t.Error("reference reported as not listed")
+	}
+	if comp, ok := c.Completeness("de"); !ok || comp != 50 {
+		t.Errorf("Completeness(de) = %v, %v; want 50, true", comp, ok)
+	}
+	if _, ok := c.Completeness("zz"); ok {
+		t.Error("Completeness of an unknown tag reported ok")
+	}
+}
+
+func TestLoadErrors(t *testing.T) {
+	if _, err := Load(fstest.MapFS{}, "en"); err == nil {
+		t.Error("Load without a locales directory returned no error")
+	}
+	if _, err := Load(testFS(map[string]string{
+		"fr/app.json": `{"a":{"defaultMessage":"Afr"}}`,
+	}), "en"); err == nil {
+		t.Error("Load without the reference returned no error")
+	}
+	if _, err := Load(testFS(map[string]string{
+		"en/app.json": `{"a":`,
+	}), "en"); err == nil {
+		t.Error("Load with a malformed reference returned no error")
+	}
+}
+
+func TestBrokenPacksSkipped(t *testing.T) {
+	c, err := Load(testFS(map[string]string{
+		"en/app.json":  `{"a":{"defaultMessage":"A"}}`,
+		"en/meta.json": metaJSON("en", "ltr"),
+		"de/app.json":  `{"a":`,
+		"de/meta.json": metaJSON("de", "ltr"),
+		"fr/app.json":  `{"a":{"defaultMessage":"Afr"}}`,
+		"fr/meta.json": `{"tag":"fr","nativeName":"x"`,
+		"es/app.json":  `{"a":{"defaultMessage":"Aes"}}`,
+		"es/meta.json": metaJSON("zz", "ltr"),
+		"it/meta.json": metaJSON("it", "ltr"),
+		"pt/app.json":  `{"a":{"defaultMessage":"Apt"}}`,
+		"pt/meta.json": metaJSON("pt", "ltr"),
+	}), "en")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := fmt.Sprint(c.Tags()); got != "[en pt]" {
+		t.Errorf("Tags() = %s; want [en pt]", got)
+	}
+	if !c.IsListed("pt") {
+		t.Error("valid pack pt not listed")
+	}
+}
+
+func TestEmptyCatalogLookup(t *testing.T) {
+	c := newCatalog("en")
+	if _, ok := c.Lookup(language.English, "a", nil); ok {
+		t.Error("empty catalog returned a message")
+	}
+	if tags := c.Tags(); len(tags) != 0 {
+		t.Errorf("empty catalog Tags() = %v", tags)
+	}
+}
+
+func TestDefaultLoadsEmbeddedPacks(t *testing.T) {
+	if _, err := Load(i18n.Locales, "en"); err != nil {
+		t.Fatalf("Load(i18n.Locales) error: %v", err)
+	}
+	tags := Tags()
+	if len(tags) == 0 || tags[0] != "en" {
+		t.Fatalf("Default().Tags() = %v; want reference first", tags)
+	}
+	if !IsListed("en") {
+		t.Error("reference not listed in the default catalog")
+	}
+	if got := Listed(); len(got) == 0 || got[0] != "en" {
+		t.Errorf("Listed() = %v; want reference first", got)
+	}
+	if _, ok := Lookup(language.English, "missing.id", nil); ok {
+		t.Error("Lookup of a missing id reported ok")
+	}
+}
diff --git a/i18n/cmd/i18n-check/fixtures_test.go b/i18n/cmd/i18n-check/fixtures_test.go
new file mode 100644
index 000000000..1b2a238bf
--- /dev/null
+++ b/i18n/cmd/i18n-check/fixtures_test.go
@@ -0,0 +1,96 @@
+package main
+
+import (
+	"bytes"
+	"errors"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"testing"
+)
+
+// allCodes lists every finding code; each has a fixture under testdata/defective.
+var allCodes = []string{
+	"malformed-pack",
+	"invalid-meta",
+	"icu-syntax",
+	"missing-placeholder",
+	"extra-placeholder",
+	"markup",
+	"unknown-id",
+	"missing-description",
+	"extract-drift",
+	"server-drift",
+	"unused-id",
+	"needs-review",
+}
+
+var codeRE = regexp.MustCompile(`\[([a-z-]+)\]`)
+
+func TestDefectiveFixtures(t *testing.T) {
+	root := filepath.Join("..", "..", "testdata", "defective")
+	for _, code := range allCodes {
+		if _, err := os.Stat(filepath.Join(root, code)); err != nil {
+			t.Errorf("fixture for %s: %v", code, err)
+		}
+	}
+
+	entries, err := os.ReadDir(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, d := range entries {
+		if !d.IsDir() {
+			continue
+		}
+		name := d.Name()
+		t.Run(name, func(t *testing.T) {
+			dir := filepath.Join(root, name)
+			var args []string
+			raw, err := os.ReadFile(filepath.Join(dir, "args"))
+			switch {
+			case err == nil:
+				for _, a := range strings.Fields(string(raw)) {
+					args = append(args, strings.ReplaceAll(a, "{dir}", dir))
+				}
+			case !errors.Is(err, fs.ErrNotExist):
+				t.Fatal(err)
+			}
+
+			var stdout, stderr bytes.Buffer
+			code := run(append(args, dir), &stdout, &stderr)
+
+			got := map[string]struct{}{}
+			for _, m := range codeRE.FindAllStringSubmatch(stdout.String(), -1) {
+				got[m[1]] = struct{}{}
+			}
+			if len(got) != 1 {
+				t.Fatalf("codes = %v; want exactly {%s}\nstdout:\n%s", keys(got), name, stdout.String())
+			}
+			if _, ok := got[name]; !ok {
+				t.Errorf("codes = %v; want {%s}\nstdout:\n%s", keys(got), name, stdout.String())
+			}
+			if stderr.Len() != 0 {
+				t.Errorf("unexpected stderr: %s", stderr.String())
+			}
+
+			want := 1
+			if name == "needs-review" {
+				want = 0
+			}
+			if code != want {
+				t.Errorf("exit = %d; want %d", code, want)
+			}
+		})
+	}
+}
+
+func keys(set map[string]struct{}) []string {
+	out := make([]string, 0, len(set))
+	for k := range set {
+		out = append(out, k)
+	}
+	return out
+}
diff --git a/i18n/cmd/i18n-check/main.go b/i18n/cmd/i18n-check/main.go
new file mode 100644
index 000000000..d345080e1
--- /dev/null
+++ b/i18n/cmd/i18n-check/main.go
@@ -0,0 +1,781 @@
+// Command i18n-check validates Gameplane's language packs.
+//
+// App mode (default) checks the reference pack and every translation under
+// <locales-dir>. It can sync the reference's server.* and notify.* entries from a
+// registry, check server.* and notify.* and extracted messages for drift, report unused ids, stamp
+// source hashes, and write the language manifest and a markdown summary.
+//
+// Module mode (--module <template.yaml>) derives the reference from the
+// template and the module.yaml beside it (package modlocale, the same ids as
+// gp-module i18n extract and the operator), requires <locales-dir>/en.json to
+// equal the derived set, and validates every other <tag>.json against it. File
+// names must be valid language tags. Without a module.yaml the module.* ids are
+// not derived, so an en.json that contains them reports unknown-id.
+//
+// Exit status: 0 when no error-severity finding was reported, 1 when one was,
+// 2 for usage errors or unreadable required files.
+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"io/fs"
+	"maps"
+	"math"
+	"os"
+	"path/filepath"
+	"slices"
+	"strings"
+
+	"github.com/GameplanePanel/gameplane/i18n/modlocale"
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+	"gopkg.in/yaml.v3"
+)
+
+const (
+	exitOK      = 0
+	exitFinding = 1
+	exitUsage   = 2
+)
+
+func main() {
+	os.Exit(run(os.Args[1:], os.Stdout, os.Stderr))
+}
+
+// options is the parsed command line.
+type options struct {
+	reference   string
+	base        string
+	extracted   string
+	registry    string
+	syncServer  bool
+	checkServer bool
+	usedIDs     string
+	manifest    string
+	stamp       bool
+	module      string
+	summary     string
+	validOut    string
+	dir         string
+}
+
+func run(args []string, stdout, stderr io.Writer) int {
+	fset := flag.NewFlagSet("i18n-check", flag.ContinueOnError)
+	fset.SetOutput(stderr)
+	var o options
+	fset.StringVar(&o.reference, "reference", "en", "reference language tag")
+	fset.StringVar(&o.base, "base", "", "previous language packs directory, for the summary's old completeness")
+	fset.StringVar(&o.extracted, "extracted", "", "formatjs-extracted messages file to compare with the reference")
+	fset.StringVar(&o.registry, "registry", "", "JSON registry of server.* and notify.* messages (required by --sync-server and --check-server)")
+	fset.BoolVar(&o.syncServer, "sync-server", false, "replace the reference's server.* and notify.* entries with the registry")
+	fset.BoolVar(&o.checkServer, "check-server", false, "report server.* and notify.* entries that differ from the registry")
+	fset.StringVar(&o.usedIDs, "used-ids", "", "file listing the message ids code uses, one per line")
+	fset.StringVar(&o.manifest, "manifest", "", "write the language manifest JSON to this file")
+	fset.BoolVar(&o.stamp, "stamp", false, "record sourceHash on translated entries that lack one")
+	fset.StringVar(&o.module, "module", "", "module mode: check flat <tag>.json packs against this template")
+	fset.StringVar(&o.summary, "summary", "", "append a markdown summary to this file")
+	fset.StringVar(&o.validOut, "valid-out", "", "write each pack's usable entries (the ones the dashboard shows) to <dir>/<tag>/app.json")
+
+	if err := fset.Parse(args); err != nil {
+		if errors.Is(err, flag.ErrHelp) {
+			return exitOK
+		}
+		return exitUsage
+	}
+	if fset.NArg() != 1 {
+		say(stderr, "i18n-check: exactly one <locales-dir> argument is required\n")
+		fset.Usage()
+		return exitUsage
+	}
+	o.dir = fset.Arg(0)
+	if err := o.checkUsage(); err != nil {
+		return fail(stderr, err)
+	}
+	if o.module != "" {
+		return runModule(o, stdout, stderr)
+	}
+	return runApp(o, stdout, stderr)
+}
+
+// checkUsage rejects flag combinations that cannot work together.
+func (o options) checkUsage() error {
+	if (o.syncServer || o.checkServer) && o.registry == "" {
+		return errors.New("--sync-server and --check-server need --registry")
+	}
+	if o.module == "" {
+		return nil
+	}
+	appOnly := []struct {
+		name string
+		set  bool
+	}{
+		{"--manifest", o.manifest != ""},
+		{"--stamp", o.stamp},
+		{"--sync-server", o.syncServer},
+		{"--check-server", o.checkServer},
+		{"--registry", o.registry != ""},
+		{"--extracted", o.extracted != ""},
+		{"--used-ids", o.usedIDs != ""},
+		{"--base", o.base != ""},
+		{"--valid-out", o.validOut != ""},
+	}
+	for _, f := range appOnly {
+		if f.set {
+			return fmt.Errorf("%s is not valid with --module", f.name)
+		}
+	}
+	return nil
+}
+
+func runApp(o options, stdout, stderr io.Writer) int {
+	refDir := filepath.Join(o.dir, o.reference)
+	refFile := o.reference + "/app.json"
+	refPath := filepath.Join(refDir, "app.json")
+	refData, err := os.ReadFile(filepath.Clean(refPath))
+	if err != nil {
+		return fail(stderr, fmt.Errorf("read reference: %w", err))
+	}
+
+	var registry map[string]pack.Entry
+	if o.syncServer || o.checkServer {
+		if registry, err = loadRegistry(o.registry); err != nil {
+			return fail(stderr, err)
+		}
+	}
+	var extracted []byte
+	if o.extracted != "" {
+		if extracted, err = os.ReadFile(filepath.Clean(o.extracted)); err != nil {
+			return fail(stderr, fmt.Errorf("read extracted messages: %w", err))
+		}
+	}
+	var used map[string]struct{}
+	if o.usedIDs != "" {
+		if used, err = readIDs(o.usedIDs); err != nil {
+			return fail(stderr, err)
+		}
+	}
+
+	ref, err := pack.ParseEntries(refData)
+	if err != nil {
+		return report(stdout, []pack.Finding{errFinding(pack.CodeMalformedPack, refFile, pack.IDPack, err.Error())})
+	}
+	if o.syncServer {
+		if err := syncServer(refPath, ref, registry); err != nil {
+			return fail(stderr, err)
+		}
+		return exitOK
+	}
+
+	findings := pack.ValidateReference(ref, refFile)
+	refMeta, _, metaFindings, err := readMeta(filepath.Join(refDir, "meta.json"), o.reference, o.reference+"/meta.json", false)
+	if err != nil {
+		return fail(stderr, err)
+	}
+	findings = append(findings, metaFindings...)
+	if o.checkServer {
+		findings = append(findings, checkServer(ref, registry, refFile)...)
+	}
+	if o.extracted != "" {
+		findings = append(findings, checkExtracted(ref, extracted, refFile)...)
+	}
+	if o.usedIDs != "" {
+		findings = append(findings, checkUsed(ref, used, refFile)...)
+	}
+
+	trs, trFindings, err := loadTranslations(o.dir, o.reference, ref)
+	if err != nil {
+		return fail(stderr, err)
+	}
+	findings = append(findings, trFindings...)
+	if o.stamp {
+		if err := stampTranslations(ref, trs); err != nil {
+			return fail(stderr, err)
+		}
+	}
+
+	if o.validOut != "" {
+		if err := writeValidPacks(o.validOut, o.reference, ref, trs); err != nil {
+			return fail(stderr, err)
+		}
+	}
+	rows := manifestRows(o.reference, refMeta, ref, trs)
+	if o.manifest != "" {
+		if err := writeManifest(o.manifest, rows); err != nil {
+			return fail(stderr, err)
+		}
+	}
+	pack.SortFindings(findings)
+	if o.summary != "" {
+		if err := writeSummary(o.summary, findings, summaryRows(o, rows)); err != nil {
+			return fail(stderr, err)
+		}
+	}
+	return report(stdout, findings)
+}
+
+func runModule(o options, stdout, stderr io.Writer) int {
+	tplData, err := os.ReadFile(filepath.Clean(o.module))
+	if err != nil {
+		return fail(stderr, fmt.Errorf("read template: %w", err))
+	}
+	derived, err := deriveModuleRefs(o.module, tplData)
+	if err != nil {
+		return fail(stderr, err)
+	}
+
+	refFile := o.reference + ".json"
+	refData, err := os.ReadFile(filepath.Clean(filepath.Join(o.dir, refFile)))
+	if err != nil {
+		return fail(stderr, fmt.Errorf("read reference: %w", err))
+	}
+	ref, err := pack.ParseEntries(refData)
+	if err != nil {
+		return report(stdout, []pack.Finding{errFinding(pack.CodeMalformedPack, refFile, pack.IDPack, err.Error())})
+	}
+	findings := pack.ValidateReference(ref, refFile)
+	// The reference must equal the ids derived from the YAML, even when that
+	// set is empty; every translation is then validated against the derived set.
+	findings = append(findings, checkModuleDrift(ref, derived, refFile)...)
+	ref = derived
+
+	dirEntries, err := os.ReadDir(o.dir)
+	if err != nil {
+		return fail(stderr, fmt.Errorf("read locales: %w", err))
+	}
+	for _, d := range dirEntries {
+		name := d.Name()
+		if d.IsDir() || name == refFile || !strings.HasSuffix(name, ".json") {
+			continue
+		}
+		if stem := strings.TrimSuffix(name, ".json"); !pack.ValidTag(stem) {
+			findings = append(findings, errFinding(pack.CodeMalformedPack, name, pack.IDPack, fmt.Sprintf("%q is not a valid language tag", stem)))
+			continue
+		}
+		data, err := os.ReadFile(filepath.Clean(filepath.Join(o.dir, name)))
+		if err != nil {
+			return fail(stderr, fmt.Errorf("read %s: %w", name, err))
+		}
+		tr, err := pack.ParseEntries(data)
+		if err != nil {
+			findings = append(findings, errFinding(pack.CodeMalformedPack, name, pack.IDPack, err.Error()))
+			continue
+		}
+		findings = append(findings, pack.ValidateTranslation(ref, tr, name)...)
+	}
+
+	pack.SortFindings(findings)
+	if o.summary != "" {
+		if err := writeSummary(o.summary, findings, nil); err != nil {
+			return fail(stderr, err)
+		}
+	}
+	return report(stdout, findings)
+}
+
+// deriveModuleRefs derives the reference pack from the template and the
+// module.yaml that sits beside it (when there is one).
+func deriveModuleRefs(templatePath string, templateData []byte) (map[string]pack.Entry, error) {
+	var tmpl map[string]any
+	if err := yaml.Unmarshal(templateData, &tmpl); err != nil {
+		return nil, fmt.Errorf("parse template: %w", err)
+	}
+	var meta map[string]any
+	metaData, err := os.ReadFile(filepath.Clean(filepath.Join(filepath.Dir(templatePath), "module.yaml")))
+	switch {
+	case err == nil:
+		if err := yaml.Unmarshal(metaData, &meta); err != nil {
+			return nil, fmt.Errorf("parse module.yaml: %w", err)
+		}
+	case !errors.Is(err, fs.ErrNotExist):
+		return nil, fmt.Errorf("read module.yaml: %w", err)
+	}
+	return modlocale.References(modlocale.Derive(meta, tmpl)), nil
+}
+
+// checkModuleDrift compares the written reference with the ids derived from
+// the template: a derived id that is missing or whose English text changed is
+// extract-drift, and an id the template no longer yields is unknown-id.
+func checkModuleDrift(ref, derived map[string]pack.Entry, file string) []pack.Finding {
+	var out []pack.Finding
+	for _, id := range slices.Sorted(maps.Keys(derived)) {
+		got, ok := ref[id]
+		switch {
+		case !ok:
+			out = append(out, errFinding(pack.CodeExtractDrift, file, id, "template references this id but the reference pack does not have it"))
+		case got.DefaultMessage != derived[id].DefaultMessage:
+			out = append(out, errFinding(pack.CodeExtractDrift, file, id, "reference text differs from the template"))
+		}
+	}
+	for _, id := range slices.Sorted(maps.Keys(ref)) {
+		if _, ok := derived[id]; !ok {
+			out = append(out, errFinding(pack.CodeUnknownID, file, id, "reference has an id the template does not use"))
+		}
+	}
+	return out
+}
+
+// translation is one non-reference app pack under the locales directory.
+type translation struct {
+	tag     string
+	dir     string
+	entries map[string]pack.Entry
+	meta    pack.Meta
+	metaOK  bool
+}
+
+// loadTranslations validates every other directory that has an app.json.
+// Directories without one are skipped. Packs that fail to parse are reported
+// and left out of the returned list.
+func loadTranslations(dir, reference string, ref map[string]pack.Entry) ([]translation, []pack.Finding, error) {
+	dirEntries, err := os.ReadDir(dir)
+	if err != nil {
+		return nil, nil, fmt.Errorf("read locales: %w", err)
+	}
+	var (
+		out      []translation
+		findings []pack.Finding
+	)
+	for _, d := range dirEntries {
+		if !d.IsDir() || d.Name() == reference {
+			continue
+		}
+		tag := d.Name()
+		packDir := filepath.Join(dir, tag)
+		file := tag + "/app.json"
+		data, err := os.ReadFile(filepath.Clean(filepath.Join(packDir, "app.json")))
+		if errors.Is(err, fs.ErrNotExist) {
+			continue
+		}
+		if err != nil {
+			return nil, nil, fmt.Errorf("read %s: %w", file, err)
+		}
+		meta, metaOK, metaFindings, err := readMeta(filepath.Join(packDir, "meta.json"), tag, tag+"/meta.json", true)
+		if err != nil {
+			return nil, nil, err
+		}
+		findings = append(findings, metaFindings...)
+		entries, err := pack.ParseEntries(data)
+		if err != nil {
+			findings = append(findings, errFinding(pack.CodeMalformedPack, file, pack.IDPack, err.Error()))
+			continue
+		}
+		findings = append(findings, pack.ValidateTranslation(ref, entries, file)...)
+		out = append(out, translation{tag: tag, dir: packDir, entries: entries, meta: meta, metaOK: metaOK})
+	}
+	return out, findings, nil
+}
+
+// readMeta reads and validates a pack's meta.json. A missing file is a finding
+// when required is set and otherwise means the pack has no metadata. Only an
+// unreadable file is returned as an error; ok reports whether the metadata is
+// usable.
+func readMeta(path, tag, file string, required bool) (meta pack.Meta, ok bool, findings []pack.Finding, err error) {
+	data, err := os.ReadFile(filepath.Clean(path))
+	if errors.Is(err, fs.ErrNotExist) {
+		if required {
+			return pack.Meta{}, false, []pack.Finding{errFinding(pack.CodeInvalidMeta, file, pack.IDMeta, "meta.json is missing")}, nil
+		}
+		return pack.Meta{}, false, nil, nil
+	}
+	if err != nil {
+		return pack.Meta{}, false, nil, fmt.Errorf("read %s: %w", file, err)
+	}
+	findings = pack.ValidateMeta(data, tag, file)
+	meta, parseErr := pack.ParseMeta(data)
+	return meta, parseErr == nil && !hasErrors(findings), findings, nil
+}
+
+// stampTranslations records the English source hash on every translated entry
+// that lacks one, and rewrites the packs it changed.
+func stampTranslations(ref map[string]pack.Entry, trs []translation) error {
+	for i := range trs {
+		tr := &trs[i]
+		stamped, changed := pack.Stamp(ref, tr.entries)
+		if !changed {
+			continue
+		}
+		tr.entries = stamped
+		data, err := pack.Marshal(tr.entries)
+		if err != nil {
+			return fmt.Errorf("stamp %s: %w", tr.tag, err)
+		}
+		if err := writeInDir(tr.dir, "app.json", data); err != nil {
+			return fmt.Errorf("write stamped %s/app.json: %w", tr.tag, err)
+		}
+	}
+	return nil
+}
+
+// writeInDir writes name inside dir through an os.Root, so the write cannot
+// escape dir whatever the directory listing or flags contained.
+func writeInDir(dir, name string, data []byte) error {
+	root, err := os.OpenRoot(dir)
+	if err != nil {
+		return fmt.Errorf("open %s: %w", dir, err)
+	}
+	defer func() { _ = root.Close() }()
+	if err := root.WriteFile(name, data, 0o600); err != nil {
+		return fmt.Errorf("write %s: %w", name, err)
+	}
+	return nil
+}
+
+// writeValidPacks writes the pack the dashboard may show for every language to
+// <dir>/<tag>/app.json. The reference pack is written whole. Other packs keep
+// only the entries pack.Valid accepts, so invalid, unknown and missing ids are
+// left out and the dashboard falls back to English for them.
+func writeValidPacks(dir, reference string, ref map[string]pack.Entry, trs []translation) error {
+	packs := map[string]map[string]pack.Entry{reference: ref}
+	for _, tr := range trs {
+		packs[tr.tag] = pack.Valid(ref, tr.entries)
+	}
+	for _, tag := range slices.Sorted(maps.Keys(packs)) {
+		data, err := pack.Marshal(packs[tag])
+		if err != nil {
+			return fmt.Errorf("valid pack %s: %w", tag, err)
+		}
+		packDir := filepath.Join(dir, tag)
+		if err := os.MkdirAll(packDir, 0o750); err != nil {
+			return fmt.Errorf("create %s: %w", packDir, err)
+		}
+		if err := writeInDir(packDir, "app.json", data); err != nil {
+			return fmt.Errorf("write valid %s/app.json: %w", tag, err)
+		}
+	}
+	return nil
+}
+
+// isRegistryID reports whether id belongs to the registry the API exports:
+// API errors (server.*) and notification text (notify.*).
+func isRegistryID(id string) bool {
+	return strings.HasPrefix(id, "server.") || strings.HasPrefix(id, "notify.")
+}
+
+// syncServer replaces the reference's server.* and notify.* entries with the
+// registry and writes the reference back.
+func syncServer(path string, ref, registry map[string]pack.Entry) error {
+	for id := range ref {
+		if isRegistryID(id) {
+			delete(ref, id)
+		}
+	}
+	maps.Copy(ref, registry)
+	data, err := pack.Marshal(ref)
+	if err != nil {
+		return err
+	}
+	if err := writeInDir(filepath.Dir(path), filepath.Base(path), data); err != nil {
+		return fmt.Errorf("write reference: %w", err)
+	}
+	return nil
+}
+
+// checkServer reports server.* and notify.* ids that exist on only one side, or
+// whose message or description differs between the reference and the registry.
+func checkServer(ref, registry map[string]pack.Entry, file string) []pack.Finding {
+	ids := map[string]struct{}{}
+	for id := range ref {
+		if isRegistryID(id) {
+			ids[id] = struct{}{}
+		}
+	}
+	for id := range registry {
+		ids[id] = struct{}{}
+	}
+	var out []pack.Finding
+	for _, id := range slices.Sorted(maps.Keys(ids)) {
+		r, inRef := ref[id]
+		g, inReg := registry[id]
+		switch {
+		case !inRef:
+			out = append(out, errFinding(pack.CodeServerDrift, file, id, "registry defines this server.* or notify.* message but the reference does not; run --sync-server"))
+		case !inReg:
+			out = append(out, errFinding(pack.CodeServerDrift, file, id, "reference has this server.* or notify.* message but the registry does not; run --sync-server"))
+		case r.DefaultMessage != g.DefaultMessage || r.Description != g.Description:
+			out = append(out, errFinding(pack.CodeServerDrift, file, id, "reference differs from the registry; run --sync-server"))
+		}
+	}
+	return out
+}
+
+// isCodeID reports whether an id is extracted from source code. Server,
+// condition and notification messages come from registries, not code.
+func isCodeID(id string) bool {
+	for _, p := range []string{"server.", "condition.", "notify."} {
+		if strings.HasPrefix(id, p) {
+			return false
+		}
+	}
+	return true
+}
+
+// checkExtracted compares the reference with the formatjs extraction for the
+// ids that come from code.
+func checkExtracted(ref map[string]pack.Entry, data []byte, file string) []pack.Finding {
+	ext, err := pack.ParseEntries(data)
+	if err != nil {
+		return []pack.Finding{errFinding(pack.CodeExtractDrift, file, pack.IDReference, "extracted messages do not parse: "+err.Error())}
+	}
+	ids := map[string]struct{}{}
+	for id := range ref {
+		if isCodeID(id) {
+			ids[id] = struct{}{}
+		}
+	}
+	for id := range ext {
+		if isCodeID(id) {
+			ids[id] = struct{}{}
+		}
+	}
+	var out []pack.Finding
+	for _, id := range slices.Sorted(maps.Keys(ids)) {
+		r, inRef := ref[id]
+		e, inExt := ext[id]
+		switch {
+		case !inExt:
+			out = append(out, errFinding(pack.CodeExtractDrift, file, id, "reference has this message but the code no longer extracts it"))
+		case !inRef:
+			out = append(out, errFinding(pack.CodeExtractDrift, file, id, "the code extracts this message but the reference does not have it"))
+		case r.DefaultMessage != e.DefaultMessage || r.Description != e.Description:
+			out = append(out, errFinding(pack.CodeExtractDrift, file, id, "reference text differs from the message extracted from the code"))
+		}
+	}
+	return out
+}
+
+// checkUsed reports reference ids that no code uses.
+func checkUsed(ref map[string]pack.Entry, used map[string]struct{}, file string) []pack.Finding {
+	var out []pack.Finding
+	for _, id := range slices.Sorted(maps.Keys(ref)) {
+		if _, ok := used[id]; !ok {
+			out = append(out, errFinding(pack.CodeUnusedID, file, id, "not used by any code; delete it from the reference"))
+		}
+	}
+	return out
+}
+
+// registryItem is one entry of the --registry JSON array.
+type registryItem struct {
+	ID          string `json:"id"`
+	English     string `json:"english"`
+	Description string `json:"description"`
+}
+
+func loadRegistry(path string) (map[string]pack.Entry, error) {
+	data, err := os.ReadFile(filepath.Clean(path))
+	if err != nil {
+		return nil, fmt.Errorf("read registry: %w", err)
+	}
+	var items []registryItem
+	if err := json.Unmarshal(data, &items); err != nil {
+		return nil, fmt.Errorf("parse registry %s: %w", path, err)
+	}
+	out := make(map[string]pack.Entry, len(items))
+	for _, it := range items {
+		out[it.ID] = pack.Entry{DefaultMessage: it.English, Description: it.Description}
+	}
+	return out, nil
+}
+
+// readIDs reads one message id per line, ignoring blank lines.
+func readIDs(path string) (map[string]struct{}, error) {
+	data, err := os.ReadFile(filepath.Clean(path))
+	if err != nil {
+		return nil, fmt.Errorf("read used ids: %w", err)
+	}
+	set := map[string]struct{}{}
+	for _, line := range strings.Split(string(data), "\n") {
+		if id := strings.TrimSpace(line); id != "" {
+			set[id] = struct{}{}
+		}
+	}
+	return set, nil
+}
+
+// manifestRow is one language in the --manifest JSON.
+type manifestRow struct {
+	Tag          string `json:"tag"`
+	NativeName   string `json:"nativeName"`
+	EnglishName  string `json:"englishName"`
+	Direction    string `json:"direction"`
+	Completeness int    `json:"completeness"`
+	Listed       bool   `json:"listed"`
+}
+
+func newRow(tag string, m pack.Meta, completeness float64, listed bool) manifestRow {
+	return manifestRow{
+		Tag:          tag,
+		NativeName:   m.NativeName,
+		EnglishName:  m.EnglishName,
+		Direction:    m.Direction,
+		Completeness: int(math.Floor(completeness)),
+		Listed:       listed,
+	}
+}
+
+// manifestRows lists the reference first, then the translations with valid
+// metadata in tag order.
+func manifestRows(reference string, refMeta pack.Meta, ref map[string]pack.Entry, trs []translation) []manifestRow {
+	rows := []manifestRow{newRow(reference, refMeta, 100, true)}
+	for _, tr := range trs {
+		if !tr.metaOK {
+			continue
+		}
+		c := pack.Completeness(ref, tr.entries)
+		rows = append(rows, newRow(tr.tag, tr.meta, c, pack.Listed(tr.tag, tr.meta, c)))
+	}
+	return rows
+}
+
+func writeManifest(path string, rows []manifestRow) error {
+	data, err := json.MarshalIndent(rows, "", "  ")
+	if err != nil {
+		return fmt.Errorf("encode manifest: %w", err)
+	}
+	// The manifest lands in a generated directory (web/src/generated/i18n,
+	// or /out in the image build) that may not exist yet.
+	if err := os.MkdirAll(filepath.Dir(filepath.Clean(path)), 0o750); err != nil {
+		return fmt.Errorf("create manifest directory: %w", err)
+	}
+	if err := os.WriteFile(path, append(data, '\n'), 0o600); err != nil {
+		return fmt.Errorf("write manifest: %w", err)
+	}
+	return nil
+}
+
+// summaryRow is one translation row of the markdown summary.
+type summaryRow struct {
+	tag          string
+	completeness string
+	listed       bool
+}
+
+// summaryRows renders completeness as "old → new" when --base is given and the
+// tag exists there, "—" → new when it does not, and plain "new" otherwise.
+func summaryRows(o options, rows []manifestRow) []summaryRow {
+	var out []summaryRow
+	for _, r := range rows {
+		if r.Tag == o.reference {
+			continue
+		}
+		cur := fmt.Sprintf("%d%%", r.Completeness)
+		if o.base != "" {
+			prev := "—"
+			if c, ok := baseCompleteness(o.base, o.reference, r.Tag); ok {
+				prev = fmt.Sprintf("%d%%", int(math.Floor(c)))
+			}
+			cur = prev + " → " + cur
+		}
+		out = append(out, summaryRow{tag: r.Tag, completeness: cur, listed: r.Listed})
+	}
+	return out
+}
+
+// baseCompleteness returns the completeness of tag's pack in the base
+// directory, measured against the base reference.
+func baseCompleteness(base, reference, tag string) (float64, bool) {
+	ref, err := readEntriesFile(filepath.Join(base, reference, "app.json"))
+	if err != nil {
+		return 0, false
+	}
+	tr, err := readEntriesFile(filepath.Join(base, tag, "app.json"))
+	if err != nil {
+		return 0, false
+	}
+	return pack.Completeness(ref, tr), true
+}
+
+func readEntriesFile(path string) (map[string]pack.Entry, error) {
+	data, err := os.ReadFile(filepath.Clean(path))
+	if err != nil {
+		return nil, fmt.Errorf("read %s: %w", path, err)
+	}
+	entries, err := pack.ParseEntries(data)
+	if err != nil {
+		return nil, fmt.Errorf("parse %s: %w", path, err)
+	}
+	return entries, nil
+}
+
+// writeSummary appends a markdown section to path: a heading, the error and
+// notice counts, an optional language table, and the findings in a code block.
+func writeSummary(path string, findings []pack.Finding, rows []summaryRow) error {
+	errs, notices := countSeverities(findings)
+	var b strings.Builder
+	_, _ = fmt.Fprintf(&b, "### i18n-check\n\n%d error(s), %d notice(s)\n\n", errs, notices)
+	if len(rows) > 0 {
+		b.WriteString("| Language | Completeness | Listed |\n| --- | --- | --- |\n")
+		for _, r := range rows {
+			listed := "no"
+			if r.listed {
+				listed = "yes"
+			}
+			_, _ = fmt.Fprintf(&b, "| %s | %s | %s |\n", r.tag, r.completeness, listed)
+		}
+		b.WriteString("\n")
+	}
+	if len(findings) > 0 {
+		b.WriteString("```text\n")
+		for _, f := range findings {
+			b.WriteString(f.String() + "\n")
+		}
+		b.WriteString("```\n")
+	}
+	out, err := os.OpenFile(filepath.Clean(path), os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o600)
+	if err != nil {
+		return fmt.Errorf("open summary: %w", err)
+	}
+	if _, err := out.WriteString(b.String()); err != nil {
+		_ = out.Close()
+		return fmt.Errorf("write summary: %w", err)
+	}
+	if err := out.Close(); err != nil {
+		return fmt.Errorf("close summary: %w", err)
+	}
+	return nil
+}
+
+// report prints the findings sorted and returns the exit status.
+func report(stdout io.Writer, findings []pack.Finding) int {
+	pack.SortFindings(findings)
+	code := exitOK
+	for _, f := range findings {
+		say(stdout, "%s\n", f.String())
+		if f.Severity == pack.SeverityError {
+			code = exitFinding
+		}
+	}
+	return code
+}
+
+func errFinding(code, file, id, msg string) pack.Finding {
+	return pack.Finding{Code: code, Severity: pack.SeverityError, File: file, ID: id, Message: msg}
+}
+
+func hasErrors(findings []pack.Finding) bool {
+	errs, _ := countSeverities(findings)
+	return errs > 0
+}
+
+func countSeverities(findings []pack.Finding) (errs, notices int) {
+	for _, f := range findings {
+		if f.Severity == pack.SeverityError {
+			errs++
+		} else {
+			notices++
+		}
+	}
+	return errs, notices
+}
+
+func fail(stderr io.Writer, err error) int {
+	say(stderr, "i18n-check: %v\n", err)
+	return exitUsage
+}
+
+func say(w io.Writer, format string, args ...any) {
+	_, _ = fmt.Fprintf(w, format, args...)
+}
diff --git a/i18n/cmd/i18n-check/main_test.go b/i18n/cmd/i18n-check/main_test.go
new file mode 100644
index 000000000..a9df7034d
--- /dev/null
+++ b/i18n/cmd/i18n-check/main_test.go
@@ -0,0 +1,334 @@
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+)
+
+func writeTree(t *testing.T, root string, files map[string]string) {
+	t.Helper()
+	for name, body := range files {
+		p := filepath.Join(root, filepath.FromSlash(name))
+		if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(p, []byte(body), 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+}
+
+func metaJSON(tag, direction string) string {
+	return fmt.Sprintf(`{"tag":%q,"nativeName":"N-%s","englishName":"E-%s","direction":%q}`, tag, tag, tag, direction)
+}
+
+// appJSON returns n reference-style entries k00..k(n-1), each with a note.
+func appJSON(t *testing.T, n int) string {
+	t.Helper()
+	m := map[string]map[string]string{}
+	for i := range n {
+		m[fmt.Sprintf("k%02d", i)] = map[string]string{
+			"defaultMessage": fmt.Sprintf("v%d", i),
+			"description":    "note",
+		}
+	}
+	data, err := json.Marshal(m)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return string(data)
+}
+
+func readFile(t *testing.T, path string) string {
+	t.Helper()
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return string(data)
+}
+
+func TestUsageErrors(t *testing.T) {
+	dir := t.TempDir()
+	writeTree(t, dir, map[string]string{
+		"en/app.json":   `{"a":{"defaultMessage":"A","description":"d"}}`,
+		"template.yaml": "id: x\n",
+	})
+	tpl := filepath.Join(dir, "template.yaml")
+	missing := filepath.Join(t.TempDir(), "missing")
+	out := filepath.Join(t.TempDir(), "manifest.json")
+
+	tests := []struct {
+		name string
+		args []string
+	}{
+		{"no locales dir", nil},
+		{"two positional args", []string{dir, dir}},
+		{"unknown flag", []string{"--bogus", dir}},
+		{"sync without registry", []string{"--sync-server", dir}},
+		{"check without registry", []string{"--check-server", dir}},
+		{"unreadable reference", []string{missing}},
+		{"unreadable registry", []string{"--check-server", "--registry", missing, dir}},
+		{"unreadable used ids", []string{"--used-ids", missing, dir}},
+		{"unreadable extracted", []string{"--extracted", missing, dir}},
+		{"module with manifest", []string{"--module", tpl, "--manifest", out, dir}},
+		{"module with stamp", []string{"--module", tpl, "--stamp", dir}},
+		{"module with sync", []string{"--module", tpl, "--sync-server", "--registry", tpl, dir}},
+		{"module missing template", []string{"--module", missing, dir}},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			var stdout, stderr bytes.Buffer
+			if got := run(tc.args, &stdout, &stderr); got != 2 {
+				t.Errorf("exit = %d; want 2 (stderr: %s)", got, stderr.String())
+			}
+			if stderr.Len() == 0 {
+				t.Error("usage error printed nothing to stderr")
+			}
+		})
+	}
+}
+
+func TestMalformedReferenceReported(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{"en/app.json": `{"a":`})
+	var stdout, stderr bytes.Buffer
+	if got := run([]string{root}, &stdout, &stderr); got != 1 {
+		t.Fatalf("exit = %d; want 1", got)
+	}
+	if !strings.Contains(stdout.String(), "[malformed-pack]") {
+		t.Errorf("stdout = %q; want a malformed-pack finding", stdout.String())
+	}
+}
+
+func TestManifestShapeAndOrder(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"en/app.json":  `{"a":{"defaultMessage":"A","description":"d"},"b":{"defaultMessage":"B","description":"d"}}`,
+		"en/meta.json": metaJSON("en", "ltr"),
+		"fr/app.json":  `{"a":{"defaultMessage":"Afr"},"b":{"defaultMessage":"Bfr"}}`,
+		"fr/meta.json": metaJSON("fr", "ltr"),
+		"de/app.json":  `{"a":{"defaultMessage":"Ade"}}`,
+		"de/meta.json": metaJSON("de", "ltr"),
+		"ar/app.json":  `{"a":{"defaultMessage":"Aar"},"b":{"defaultMessage":"Bar"}}`,
+		"ar/meta.json": metaJSON("ar", "rtl"),
+		"xx/app.json":  `{"a":{"defaultMessage":"Axx"}}`,
+	})
+	manifest := filepath.Join(t.TempDir(), "manifest.json")
+	var stdout, stderr bytes.Buffer
+	// Exit 1 is expected: xx has no meta.json, which is an error-severity
+	// invalid-meta finding. xx is still skipped from the manifest.
+	if got := run([]string{"--manifest", manifest, root}, &stdout, &stderr); got != 1 {
+		t.Fatalf("exit = %d; want 1 for xx without meta.json (stdout: %s, stderr: %s)", got, stdout.String(), stderr.String())
+	}
+
+	data := readFile(t, manifest)
+	if !strings.HasSuffix(data, "]\n") {
+		t.Errorf("manifest does not end with a newline: %q", data)
+	}
+	var rows []manifestRow
+	if err := json.Unmarshal([]byte(data), &rows); err != nil {
+		t.Fatal(err)
+	}
+	want := []manifestRow{
+		{Tag: "en", NativeName: "N-en", EnglishName: "E-en", Direction: "ltr", Completeness: 100, Listed: true},
+		{Tag: "ar", NativeName: "N-ar", EnglishName: "E-ar", Direction: "rtl", Completeness: 100, Listed: false},
+		{Tag: "de", NativeName: "N-de", EnglishName: "E-de", Direction: "ltr", Completeness: 50, Listed: false},
+		{Tag: "fr", NativeName: "N-fr", EnglishName: "E-fr", Direction: "ltr", Completeness: 100, Listed: true},
+	}
+	if fmt.Sprint(rows) != fmt.Sprint(want) {
+		t.Errorf("manifest rows =\n%+v\nwant\n%+v", rows, want)
+	}
+}
+
+func TestSummaryShowsCompletenessChange(t *testing.T) {
+	base := t.TempDir()
+	writeTree(t, base, map[string]string{
+		"en/app.json": appJSON(t, 20),
+		"fr/app.json": appJSON(t, 8),
+	})
+	cur := t.TempDir()
+	writeTree(t, cur, map[string]string{
+		"en/app.json":  appJSON(t, 20),
+		"en/meta.json": metaJSON("en", "ltr"),
+		"fr/app.json":  appJSON(t, 17),
+		"fr/meta.json": metaJSON("fr", "ltr"),
+	})
+	summary := filepath.Join(t.TempDir(), "summary.md")
+	if err := os.WriteFile(summary, []byte("existing\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	var stdout, stderr bytes.Buffer
+	if got := run([]string{"--base", base, "--summary", summary, cur}, &stdout, &stderr); got != 0 {
+		t.Fatalf("exit = %d; want 0 (stdout: %s)", got, stdout.String())
+	}
+	got := readFile(t, summary)
+	for _, want := range []string{"existing\n", "### i18n-check", "0 error(s), 0 notice(s)", "| fr | 40% → 85% | yes |"} {
+		if !strings.Contains(got, want) {
+			t.Errorf("summary missing %q:\n%s", want, got)
+		}
+	}
+}
+
+func TestStampWritesSourceHash(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"en/app.json":  `{"a":{"defaultMessage":"A","description":"d"}}`,
+		"fr/app.json":  `{"a":{"defaultMessage":"Afr"}}`,
+		"fr/meta.json": metaJSON("fr", "ltr"),
+	})
+	var stdout, stderr bytes.Buffer
+	if got := run([]string{"--stamp", root}, &stdout, &stderr); got != 0 {
+		t.Fatalf("exit = %d; want 0 (stdout: %s)", got, stdout.String())
+	}
+	entries, err := pack.ParseEntries([]byte(readFile(t, filepath.Join(root, "fr", "app.json"))))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want := pack.SourceHash("A"); entries["a"].SourceHash != want {
+		t.Errorf("sourceHash = %q; want %q", entries["a"].SourceHash, want)
+	}
+	if strings.Contains(readFile(t, filepath.Join(root, "en", "app.json")), "sourceHash") {
+		t.Error("reference was stamped")
+	}
+}
+
+func TestSyncServerWritesRegistry(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"en/app.json": `{"a":{"defaultMessage":"A","description":"d"},"server.old":{"defaultMessage":"Old","description":"x"}}`,
+	})
+	registry := filepath.Join(t.TempDir(), "registry.json")
+	if err := os.WriteFile(registry, []byte(`[{"id":"server.new","english":"New","description":"Shown"}]`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	var stdout, stderr bytes.Buffer
+	if got := run([]string{"--sync-server", "--registry", registry, root}, &stdout, &stderr); got != 0 {
+		t.Fatalf("exit = %d; want 0 (stderr: %s)", got, stderr.String())
+	}
+	entries, err := pack.ParseEntries([]byte(readFile(t, filepath.Join(root, "en", "app.json"))))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := entries["server.old"]; ok {
+		t.Error("server.old survived the sync")
+	}
+	if got := entries["server.new"]; got.DefaultMessage != "New" || got.Description != "Shown" {
+		t.Errorf("server.new = %+v; want registry values", got)
+	}
+	if _, ok := entries["a"]; !ok {
+		t.Error("non-server entry was dropped by the sync")
+	}
+}
+
+func TestCheckServerRegistryAndReferenceOnlyIDs(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"en/app.json": `{"a":{"defaultMessage":"A","description":"d"},"server.only-ref":{"defaultMessage":"R","description":"d"}}`,
+	})
+	registry := filepath.Join(t.TempDir(), "registry.json")
+	if err := os.WriteFile(registry, []byte(`[{"id":"server.only-reg","english":"G","description":"d"}]`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	var stdout, stderr bytes.Buffer
+	if got := run([]string{"--check-server", "--registry", registry, root}, &stdout, &stderr); got != 1 {
+		t.Fatalf("exit = %d; want 1 (stdout: %s, stderr: %s)", got, stdout.String(), stderr.String())
+	}
+	for _, want := range []string{"server.only-ref: [server-drift]", "server.only-reg: [server-drift]"} {
+		if !strings.Contains(stdout.String(), want) {
+			t.Errorf("stdout missing %q:\n%s", want, stdout.String())
+		}
+	}
+}
+
+func TestExtractedUnparseableReported(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"en/app.json": `{"a":{"defaultMessage":"A","description":"d"}}`,
+	})
+	extracted := filepath.Join(t.TempDir(), "extracted.json")
+	if err := os.WriteFile(extracted, []byte(`{"a":`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	var stdout, stderr bytes.Buffer
+	if got := run([]string{"--extracted", extracted, root}, &stdout, &stderr); got != 1 {
+		t.Fatalf("exit = %d; want 1 (stdout: %s, stderr: %s)", got, stdout.String(), stderr.String())
+	}
+	if !strings.Contains(stdout.String(), "[extract-drift]") {
+		t.Errorf("stdout = %q; want an extract-drift finding", stdout.String())
+	}
+}
+
+func TestExtractedMissingAndExtraIDs(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"en/app.json": `{"a":{"defaultMessage":"A","description":"d"},"b":{"defaultMessage":"B","description":"d"}}`,
+	})
+	extracted := filepath.Join(t.TempDir(), "extracted.json")
+	if err := os.WriteFile(extracted, []byte(`{"a":{"defaultMessage":"A","description":"d"},"c":{"defaultMessage":"C","description":"d"}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	var stdout, stderr bytes.Buffer
+	if got := run([]string{"--extracted", extracted, root}, &stdout, &stderr); got != 1 {
+		t.Fatalf("exit = %d; want 1 (stdout: %s, stderr: %s)", got, stdout.String(), stderr.String())
+	}
+	for _, want := range []string{": b: [extract-drift]", ": c: [extract-drift]"} {
+		if !strings.Contains(stdout.String(), want) {
+			t.Errorf("stdout missing %q:\n%s", want, stdout.String())
+		}
+	}
+	if strings.Contains(stdout.String(), ": a: [extract-drift]") {
+		t.Errorf("matching id a was reported:\n%s", stdout.String())
+	}
+}
+
+func TestSummaryUnwritablePathIsUsageError(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"en/app.json": `{"a":{"defaultMessage":"A","description":"d"}}`,
+	})
+	summary := filepath.Join(t.TempDir(), "missing-dir", "summary.md")
+	var stdout, stderr bytes.Buffer
+	if got := run([]string{"--summary", summary, root}, &stdout, &stderr); got != 2 {
+		t.Fatalf("exit = %d; want 2 (stdout: %s)", got, stdout.String())
+	}
+	if stderr.Len() == 0 {
+		t.Error("unwritable summary printed nothing to stderr")
+	}
+}
+
+func TestModulePacks(t *testing.T) {
+	tests := []struct {
+		name string
+		fr   string
+		want int
+	}{
+		{"clean", `{"template.displayName":{"defaultMessage":"Afr"}}`, 0},
+		{"placeholder mismatch", `{"template.displayName":{"defaultMessage":"{x}"}}`, 1},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			root := t.TempDir()
+			writeTree(t, root, map[string]string{
+				"en.json": `{"template.displayName":{"defaultMessage":"A","description":"d"}}`,
+				"fr.json": tc.fr,
+			})
+			tpl := filepath.Join(t.TempDir(), "template.yaml")
+			if err := os.WriteFile(tpl, []byte("spec:\n  displayName: A\n"), 0o644); err != nil {
+				t.Fatal(err)
+			}
+			var stdout, stderr bytes.Buffer
+			if got := run([]string{"--module", tpl, root}, &stdout, &stderr); got != tc.want {
+				t.Errorf("exit = %d; want %d (stdout: %s)", got, tc.want, stdout.String())
+			}
+		})
+	}
+}
diff --git a/i18n/cmd/i18n-check/module_ids_test.go b/i18n/cmd/i18n-check/module_ids_test.go
new file mode 100644
index 000000000..55fdbd8bb
--- /dev/null
+++ b/i18n/cmd/i18n-check/module_ids_test.go
@@ -0,0 +1,150 @@
+package main
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const derivedTemplate = `apiVersion: gameplane.io/v1alpha1
+kind: GameTemplate
+spec:
+  displayName: Template
+  configSchema:
+    - name: MAX_PLAYERS
+      displayName: Max players
+`
+
+func runModuleCheck(t *testing.T, files map[string]string, template, moduleYAML string) (int, string) {
+	t.Helper()
+	root := t.TempDir()
+	writeTree(t, root, files)
+	modDir := t.TempDir()
+	tpl := filepath.Join(modDir, "template.yaml")
+	if err := os.WriteFile(tpl, []byte(template), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if moduleYAML != "" {
+		if err := os.WriteFile(filepath.Join(modDir, "module.yaml"), []byte(moduleYAML), 0o600); err != nil {
+			t.Fatal(err)
+		}
+	}
+	var stdout, stderr bytes.Buffer
+	code := run([]string{"--module", tpl, root}, &stdout, &stderr)
+	return code, stdout.String() + stderr.String()
+}
+
+func derivedReference() string {
+	return `{
+  "template.displayName": {"defaultMessage": "Template", "description": "d"},
+  "config.MAX_PLAYERS.displayName": {"defaultMessage": "Max players", "description": "d"},
+  "module.summary": {"defaultMessage": "Sum", "description": "d"}
+}`
+}
+
+func TestModuleDerivedReferenceMatches(t *testing.T) {
+	code, out := runModuleCheck(t, map[string]string{
+		"en.json": derivedReference(),
+		"fr.json": `{"template.displayName":{"defaultMessage":"Modèle"}}`,
+	}, derivedTemplate, "displayName: Mod\nsummary: Sum\n")
+	// module.displayName is derived too, so the reference is missing it.
+	if code != 1 || !strings.Contains(out, "module.displayName") {
+		t.Fatalf("exit = %d, want 1 naming module.displayName: %s", code, out)
+	}
+}
+
+func TestModuleDerivedReferenceClean(t *testing.T) {
+	code, out := runModuleCheck(t, map[string]string{
+		"en.json": derivedReference(),
+		"fr.json": `{"template.displayName":{"defaultMessage":"Modèle"}}`,
+	}, derivedTemplate, "summary: Sum\n")
+	if code != 0 {
+		t.Fatalf("exit = %d: %s", code, out)
+	}
+}
+
+func TestModuleUnknownReferenceID(t *testing.T) {
+	code, out := runModuleCheck(t, map[string]string{
+		"en.json": strings.Replace(derivedReference(), "}\n}", "},\n  \"stale.id\": {\"defaultMessage\": \"x\", \"description\": \"d\"}\n}", 1),
+	}, derivedTemplate, "summary: Sum\n")
+	if code != 1 || !strings.Contains(out, "stale.id") || !strings.Contains(out, "unknown-id") {
+		t.Fatalf("exit = %d: %s", code, out)
+	}
+}
+
+func TestModuleChangedReferenceText(t *testing.T) {
+	code, out := runModuleCheck(t, map[string]string{
+		"en.json": strings.Replace(derivedReference(), `"Template"`, `"Changed"`, 1),
+	}, derivedTemplate, "summary: Sum\n")
+	if code != 1 || !strings.Contains(out, "extract-drift") {
+		t.Fatalf("exit = %d: %s", code, out)
+	}
+}
+
+func TestModuleTranslationUsesDerivedReference(t *testing.T) {
+	code, out := runModuleCheck(t, map[string]string{
+		"en.json": derivedReference(),
+		"fr.json": `{"template.displayName":{"defaultMessage":"{extra}"},"nope":{"defaultMessage":"x"}}`,
+	}, derivedTemplate, "summary: Sum\n")
+	if code != 1 || !strings.Contains(out, "extra-placeholder") || !strings.Contains(out, "unknown-id") {
+		t.Fatalf("exit = %d: %s", code, out)
+	}
+}
+
+func TestModuleInvalidTemplateYAML(t *testing.T) {
+	code, out := runModuleCheck(t, map[string]string{
+		"en.json": derivedReference(),
+	}, "spec: [unterminated\n", "")
+	if code != 2 || !strings.Contains(out, "parse template") {
+		t.Fatalf("exit = %d: %s", code, out)
+	}
+}
+
+func TestModuleInvalidModuleYAML(t *testing.T) {
+	code, out := runModuleCheck(t, map[string]string{
+		"en.json": derivedReference(),
+	}, derivedTemplate, "summary: [unterminated\n")
+	if code != 2 || !strings.Contains(out, "parse module.yaml") {
+		t.Fatalf("exit = %d: %s", code, out)
+	}
+}
+
+func TestModuleReferenceWithIDsButTemplateDerivesNone(t *testing.T) {
+	code, out := runModuleCheck(t, map[string]string{
+		"en.json": `{"template.displayName": {"defaultMessage": "Template", "description": "d"}}`,
+	}, "spec: {}\n", "")
+	if code != 1 || !strings.Contains(out, "unknown-id") || !strings.Contains(out, "template.displayName") {
+		t.Fatalf("exit = %d: %s", code, out)
+	}
+}
+
+func TestModuleEmptyReferenceAndEmptyTemplate(t *testing.T) {
+	code, out := runModuleCheck(t, map[string]string{"en.json": `{}`}, "spec: {}\n", "")
+	if code != 0 {
+		t.Fatalf("exit = %d: %s", code, out)
+	}
+}
+
+func TestModuleInvalidTranslationFileNames(t *testing.T) {
+	for _, name := range []string{"xx_YY.json", "Fr.json"} {
+		code, out := runModuleCheck(t, map[string]string{
+			"en.json": derivedReference(),
+			name:      `{}`,
+		}, derivedTemplate, "summary: Sum\n")
+		if code != 1 || !strings.Contains(out, name) || !strings.Contains(out, "malformed-pack") {
+			t.Fatalf("%s: exit = %d: %s", name, code, out)
+		}
+	}
+}
+
+func TestModuleTranslationUsingIDOnlyInReferenceIsUnknown(t *testing.T) {
+	code, out := runModuleCheck(t, map[string]string{
+		"en.json": derivedReference(),
+		"fr.json": `{"only.in.en":{"defaultMessage":"x"}}`,
+	}, derivedTemplate, "summary: Sum\n")
+	if code != 1 || !strings.Contains(out, "unknown-id") || !strings.Contains(out, "only.in.en") {
+		t.Fatalf("exit = %d: %s", code, out)
+	}
+}
diff --git a/i18n/cmd/i18n-check/notify_registry_test.go b/i18n/cmd/i18n-check/notify_registry_test.go
new file mode 100644
index 000000000..f13065c4b
--- /dev/null
+++ b/i18n/cmd/i18n-check/notify_registry_test.go
@@ -0,0 +1,56 @@
+package main
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+)
+
+func TestSyncRegistryCarriesNotifyEntries(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"en/app.json": `{"a":{"defaultMessage":"A","description":"d"},"server.a":{"defaultMessage":"Old","description":"x"},"notify.old":{"defaultMessage":"Stale","description":"x"}}`,
+	})
+	registry := filepath.Join(t.TempDir(), "registry.json")
+	if err := os.WriteFile(registry, []byte(`[{"id":"server.a","english":"A2","description":"d2"},{"id":"notify.b","english":"B","description":"Shown"}]`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	var stdout, stderr bytes.Buffer
+	if got := run([]string{"--sync-server", "--registry", registry, root}, &stdout, &stderr); got != 0 {
+		t.Fatalf("exit = %d; want 0 (stderr: %s)", got, stderr.String())
+	}
+	entries, err := pack.ParseEntries([]byte(readFile(t, filepath.Join(root, "en", "app.json"))))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := entries["server.a"]; got.DefaultMessage != "A2" {
+		t.Errorf("server.a = %+v; want registry value", got)
+	}
+	if got := entries["notify.b"]; got.DefaultMessage != "B" || got.Description != "Shown" {
+		t.Errorf("notify.b = %+v; want registry values", got)
+	}
+	if _, ok := entries["notify.old"]; ok {
+		t.Error("notify.old survived the sync")
+	}
+	if _, ok := entries["a"]; !ok {
+		t.Error("non-registry entry was dropped by the sync")
+	}
+}
+
+func TestCheckRegistryReportsStaleNotifyEntry(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"en/app.json": `{"notify.stale":{"defaultMessage":"S","description":"d"}}`,
+	})
+	registry := filepath.Join(t.TempDir(), "registry.json")
+	if err := os.WriteFile(registry, []byte(`[]`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	var stdout, stderr bytes.Buffer
+	if got := run([]string{"--check-server", "--registry", registry, root}, &stdout, &stderr); got != 1 {
+		t.Fatalf("exit = %d; want 1 (stdout: %s, stderr: %s)", got, stdout.String(), stderr.String())
+	}
+}
diff --git a/i18n/cmd/i18n-check/valid_test.go b/i18n/cmd/i18n-check/valid_test.go
new file mode 100644
index 000000000..3a9469b64
--- /dev/null
+++ b/i18n/cmd/i18n-check/valid_test.go
@@ -0,0 +1,116 @@
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"testing"
+
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+)
+
+// partialPack returns a French-style pack that translates the first translated
+// ids of a reference built by appJSON.
+func partialPack(t *testing.T, translated int) string {
+	t.Helper()
+	m := map[string]map[string]string{}
+	for i := range translated {
+		m[fmt.Sprintf("k%02d", i)] = map[string]string{"defaultMessage": fmt.Sprintf("f%d", i)}
+	}
+	data, err := json.Marshal(m)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return string(data)
+}
+
+func TestManifestListingThreshold(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"en/app.json":  appJSON(t, 10),
+		"en/meta.json": metaJSON("en", "ltr"),
+		"fr/app.json":  partialPack(t, 7), // 70%: below the listing threshold
+		"fr/meta.json": metaJSON("fr", "ltr"),
+		"de/app.json":  partialPack(t, 9), // 90%: listed
+		"de/meta.json": metaJSON("de", "ltr"),
+	})
+	manifest := filepath.Join(t.TempDir(), "languages.json")
+	var stdout, stderr bytes.Buffer
+	if got := run([]string{"--manifest", manifest, root}, &stdout, &stderr); got != exitOK {
+		t.Fatalf("exit = %d; want %d (stdout: %s)", got, exitOK, stdout.String())
+	}
+	var rows []manifestRow
+	if err := json.Unmarshal([]byte(readFile(t, manifest)), &rows); err != nil {
+		t.Fatal(err)
+	}
+	listed := map[string]bool{}
+	completeness := map[string]int{}
+	for _, r := range rows {
+		listed[r.Tag] = r.Listed
+		completeness[r.Tag] = r.Completeness
+	}
+	if completeness["fr"] != 70 || listed["fr"] {
+		t.Errorf("fr: completeness %d listed %v; want 70 and not listed", completeness["fr"], listed["fr"])
+	}
+	if completeness["de"] != 90 || !listed["de"] {
+		t.Errorf("de: completeness %d listed %v; want 90 and listed", completeness["de"], listed["de"])
+	}
+	if !listed["en"] {
+		t.Error("en is not listed")
+	}
+}
+
+func TestValidOutKeepsUsableEntries(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"en/app.json":  `{"a":{"defaultMessage":"Hi {name}"},"b":{"defaultMessage":"Plain"}}`,
+		"en/meta.json": metaJSON("en", "ltr"),
+		// "a" is usable; "b" adds a placeholder English does not have, and
+		// "zz" is an id the reference no longer has.
+		"fr/app.json":  `{"a":{"defaultMessage":"Salut {name}"},"b":{"defaultMessage":"Simple {name}"},"zz":{"defaultMessage":"Extra"}}`,
+		"fr/meta.json": metaJSON("fr", "ltr"),
+	})
+	out := t.TempDir()
+	var stdout, stderr bytes.Buffer
+	// Findings make the exit status 1 here; only usage errors must not occur.
+	if got := run([]string{"--valid-out", out, root}, &stdout, &stderr); got == exitUsage {
+		t.Fatalf("exit = %d; want a non-usage status (stderr: %s)", got, stderr.String())
+	}
+	fr, err := pack.ParseEntries([]byte(readFile(t, filepath.Join(out, "fr", "app.json"))))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := sortedKeys(fr); len(got) != 1 || got[0] != "a" {
+		t.Errorf("fr ids = %v; want [a]", got)
+	}
+	en, err := pack.ParseEntries([]byte(readFile(t, filepath.Join(out, "en", "app.json"))))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := sortedKeys(en); len(got) != 2 {
+		t.Errorf("en ids = %v; want the whole reference", got)
+	}
+}
+
+func TestValidOutIsUsageErrorWithModule(t *testing.T) {
+	dir := t.TempDir()
+	var stdout, stderr bytes.Buffer
+	if got := run([]string{"--module", dir, "--valid-out", dir, dir}, &stdout, &stderr); got != exitUsage {
+		t.Errorf("exit = %d; want %d", got, exitUsage)
+	}
+	if _, err := os.Stat(filepath.Join(dir, "fr")); err == nil {
+		t.Error("module mode wrote packs")
+	}
+}
+
+func sortedKeys(m map[string]pack.Entry) []string {
+	keys := make([]string, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys
+}
diff --git a/i18n/doc.go b/i18n/doc.go
new file mode 100644
index 000000000..010f4f04d
--- /dev/null
+++ b/i18n/doc.go
@@ -0,0 +1,8 @@
+// Package i18n holds Gameplane's shared language packs: the English reference
+// catalog, the translated packs under locales/, and the embedded file system
+// that other modules import at build time.
+//
+// The ICU message formatter lives in package icu, pack validation in package
+// pack, runtime lookup in package catalog, and the CI checker in
+// cmd/i18n-check.
+package i18n
diff --git a/i18n/embed.go b/i18n/embed.go
new file mode 100644
index 000000000..4db0d8ac5
--- /dev/null
+++ b/i18n/embed.go
@@ -0,0 +1,11 @@
+package i18n
+
+import "embed"
+
+// Locales holds every language pack under locales/<tag>/, including the
+// English reference (locales/en/app.json). go:embed paths cannot contain "..",
+// so the embed directive must live in this root package while the consumers
+// (package catalog) read the files from here.
+//
+//go:embed locales/*/*.json
+var Locales embed.FS
diff --git a/i18n/go.mod b/i18n/go.mod
new file mode 100644
index 000000000..4f03ea0eb
--- /dev/null
+++ b/i18n/go.mod
@@ -0,0 +1,8 @@
+module github.com/GameplanePanel/gameplane/i18n
+
+go 1.26.0
+
+require (
+	golang.org/x/text v0.42.0
+	gopkg.in/yaml.v3 v3.0.1
+)
diff --git a/i18n/go.sum b/i18n/go.sum
new file mode 100644
index 000000000..a23a509ff
--- /dev/null
+++ b/i18n/go.sum
@@ -0,0 +1,6 @@
+golang.org/x/text v0.42.0 h1:JbOZXgfeCPU9gacVtYliJqOhD+zhrEqK4LfdpmlUZqI=
+golang.org/x/text v0.42.0/go.mod h1:ojzP1Z+2QtioaF8DTtO8K5q7JWVVYwZKenzujK0Zd0E=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/i18n/icu/format.go b/i18n/icu/format.go
new file mode 100644
index 000000000..4fafea506
--- /dev/null
+++ b/i18n/icu/format.go
@@ -0,0 +1,240 @@
+package icu
+
+import (
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+	"time"
+
+	"golang.org/x/text/feature/plural"
+	"golang.org/x/text/language"
+	"golang.org/x/text/message"
+	"golang.org/x/text/number"
+)
+
+// state carries the locale, the arguments and the current plural value (for #)
+// through a recursive render.
+type state struct {
+	tag      language.Tag
+	args     map[string]any
+	pound    string
+	hasPound bool
+}
+
+// Format renders m for tag using args. A missing argument renders as {name}.
+// Format never panics on a malformed message; unknown shapes render as text.
+func Format(m Message, tag language.Tag, args map[string]any) string {
+	var b strings.Builder
+	writeNodes(&b, m, state{tag: tag, args: args})
+	return b.String()
+}
+
+func writeNodes(b *strings.Builder, nodes []Node, st state) {
+	for _, n := range nodes {
+		switch n.Kind {
+		case KindLiteral:
+			b.WriteString(n.Text)
+		case KindPound:
+			if st.hasPound {
+				b.WriteString(st.pound)
+			} else {
+				b.WriteByte('#')
+			}
+		case KindTag:
+			b.WriteString("<" + n.Name + ">")
+			writeNodes(b, n.Children, st)
+			b.WriteString("</" + n.Name + ">")
+		case KindArgument:
+			v, ok := st.args[n.Name]
+			if !ok {
+				b.WriteString("{" + n.Name + "}")
+				continue
+			}
+			b.WriteString(formatArgument(v, n, st.tag))
+		case KindPlural:
+			v, ok := st.args[n.Name]
+			if !ok {
+				b.WriteString("{" + n.Name + "}")
+				continue
+			}
+			writePlural(b, n, v, st)
+		case KindSelect:
+			v, ok := st.args[n.Name]
+			if !ok {
+				writeOption(b, findOption(n.Options, "other"), st, "", false)
+				continue
+			}
+			opt := findOption(n.Options, fmt.Sprint(v))
+			if opt == nil {
+				opt = findOption(n.Options, "other")
+			}
+			writeOption(b, opt, st, "", false)
+		}
+	}
+}
+
+// writePlural renders the branch selected by an exact =N match, else by the
+// CLDR plural category of the value, else the other branch.
+func writePlural(b *strings.Builder, n Node, v any, st state) {
+	val, text, ok := toNumber(v)
+	if !ok {
+		writeOption(b, findOption(n.Options, "other"), st, fmt.Sprint(v), true)
+		return
+	}
+	x, _ := strconv.ParseFloat(text, 64)
+	opt := exactOption(n.Options, x)
+	if opt == nil {
+		opt = findOption(n.Options, pluralKey(st.tag, text))
+	}
+	if opt == nil {
+		opt = findOption(n.Options, "other")
+	}
+	pound := message.NewPrinter(st.tag).Sprint(number.Decimal(val))
+	writeOption(b, opt, st, pound, true)
+}
+
+func writeOption(b *strings.Builder, opt *Option, st state, pound string, hasPound bool) {
+	if opt == nil {
+		return
+	}
+	inner := st
+	if hasPound {
+		inner.pound = pound
+		inner.hasPound = true
+	}
+	writeNodes(b, opt.Value, inner)
+}
+
+func findOption(opts []Option, key string) *Option {
+	for i := range opts {
+		if opts[i].Key == key {
+			return &opts[i]
+		}
+	}
+	return nil
+}
+
+func exactOption(opts []Option, x float64) *Option {
+	for i := range opts {
+		k := opts[i].Key
+		if !strings.HasPrefix(k, "=") {
+			continue
+		}
+		n, err := strconv.Atoi(k[1:])
+		if err == nil && x == float64(n) {
+			return &opts[i]
+		}
+	}
+	return nil
+}
+
+// pluralKey maps the CLDR category of a decimal string to its option key.
+func pluralKey(tag language.Tag, text string) string {
+	i, v, w, f, t := operands(text)
+	switch plural.Cardinal.MatchPlural(tag, i, v, w, f, t) {
+	case plural.Zero:
+		return "zero"
+	case plural.One:
+		return "one"
+	case plural.Two:
+		return "two"
+	case plural.Few:
+		return "few"
+	case plural.Many:
+		return "many"
+	default:
+		return "other"
+	}
+}
+
+// operands derives the CLDR plural operands i, v, w, f and t from a plain
+// decimal string such as "-12.50". Operands too large for an int keep their
+// last seven digits, as the CLDR rules permit.
+func operands(text string) (i, v, w, f, t int) {
+	text = strings.TrimPrefix(text, "-")
+	intPart, frac, _ := strings.Cut(text, ".")
+	fracTrim := strings.TrimRight(frac, "0")
+	i = tailInt(intPart)
+	v = len(frac)
+	w = len(fracTrim)
+	f = tailInt(frac)
+	t = tailInt(fracTrim)
+	return i, v, w, f, t
+}
+
+// tailInt parses the last seven digits of s; empty input yields 0.
+func tailInt(s string) int {
+	const keep = 7
+	if len(s) > keep {
+		s = s[len(s)-keep:]
+	}
+	n, err := strconv.Atoi(s)
+	if err != nil {
+		return 0
+	}
+	return n
+}
+
+// toNumber reports whether v is numeric (a Go numeric type or a numeric
+// string). It returns the value for number.Decimal and its plain decimal text.
+func toNumber(v any) (val any, text string, ok bool) {
+	switch t := v.(type) {
+	case int:
+		return t, strconv.FormatInt(int64(t), 10), true
+	case int8:
+		return t, strconv.FormatInt(int64(t), 10), true
+	case int16:
+		return t, strconv.FormatInt(int64(t), 10), true
+	case int32:
+		return t, strconv.FormatInt(int64(t), 10), true
+	case int64:
+		return t, strconv.FormatInt(t, 10), true
+	case uint:
+		return t, strconv.FormatUint(uint64(t), 10), true
+	case uint8:
+		return t, strconv.FormatUint(uint64(t), 10), true
+	case uint16:
+		return t, strconv.FormatUint(uint64(t), 10), true
+	case uint32:
+		return t, strconv.FormatUint(uint64(t), 10), true
+	case uint64:
+		return t, strconv.FormatUint(t, 10), true
+	case float32:
+		f := float64(t)
+		if math.IsNaN(f) || math.IsInf(f, 0) {
+			return nil, "", false
+		}
+		return f, strconv.FormatFloat(f, 'f', -1, 32), true
+	case float64:
+		if math.IsNaN(t) || math.IsInf(t, 0) {
+			return nil, "", false
+		}
+		return t, strconv.FormatFloat(t, 'f', -1, 64), true
+	case string:
+		f, err := strconv.ParseFloat(strings.TrimSpace(t), 64)
+		if err != nil || math.IsNaN(f) || math.IsInf(f, 0) {
+			return nil, "", false
+		}
+		return f, strconv.FormatFloat(f, 'f', -1, 64), true
+	}
+	return nil, "", false
+}
+
+func formatArgument(v any, n Node, tag language.Tag) string {
+	switch n.Format {
+	case "number":
+		if val, _, ok := toNumber(v); ok {
+			return message.NewPrinter(tag).Sprint(number.Decimal(val))
+		}
+	case "date":
+		if t, ok := v.(time.Time); ok {
+			return t.Format("2006-01-02")
+		}
+	case "time":
+		if t, ok := v.(time.Time); ok {
+			return t.Format("15:04")
+		}
+	}
+	return fmt.Sprint(v)
+}
diff --git a/i18n/icu/format_test.go b/i18n/icu/format_test.go
new file mode 100644
index 000000000..eb0466ea6
--- /dev/null
+++ b/i18n/icu/format_test.go
@@ -0,0 +1,269 @@
+package icu
+
+import (
+	"fmt"
+	"math"
+	"testing"
+	"time"
+
+	"golang.org/x/text/language"
+)
+
+func TestFormatNumericTypes(t *testing.T) {
+	plural, err := Parse("{n, plural, one {# item} other {# items}}")
+	if err != nil {
+		t.Fatal(err)
+	}
+	number, err := Parse("{n, number}")
+	if err != nil {
+		t.Fatal(err)
+	}
+	values := []any{
+		int(3), int8(3), int16(3), int32(3), int64(3),
+		uint(3), uint8(3), uint16(3), uint32(3), uint64(3),
+		float32(3),
+	}
+	for _, v := range values {
+		name := fmt.Sprintf("%T", v)
+		if got := Format(plural, language.English, map[string]any{"n": v}); got != "3 items" {
+			t.Errorf("plural with %s = %q; want %q", name, got, "3 items")
+		}
+		if got := Format(number, language.English, map[string]any{"n": v}); got != "3" {
+			t.Errorf("number with %s = %q; want %q", name, got, "3")
+		}
+	}
+	// NaN and +Inf have no meaningful count; they must still render without panicking.
+	for _, v := range []float64{math.NaN(), math.Inf(1)} {
+		if got := Format(plural, language.English, map[string]any{"n": v}); got == "" {
+			t.Errorf("plural with %v rendered empty", v)
+		}
+		if got := Format(number, language.English, map[string]any{"n": v}); got == "" {
+			t.Errorf("number with %v rendered empty", v)
+		}
+	}
+}
+
+func TestFormat(t *testing.T) {
+	tests := []struct {
+		name string
+		tag  language.Tag
+		in   string
+		args map[string]any
+		want string
+	}{
+		{
+			name: "french plural zero",
+			tag:  language.French,
+			in:   "{n, plural, one {# fichier} other {# fichiers}}",
+			args: map[string]any{"n": 0},
+			want: "0 fichier",
+		},
+		{
+			name: "french plural one",
+			tag:  language.French,
+			in:   "{n, plural, one {# fichier} other {# fichiers}}",
+			args: map[string]any{"n": 1},
+			want: "1 fichier",
+		},
+		{
+			name: "french plural other",
+			tag:  language.French,
+			in:   "{n, plural, one {# fichier} other {# fichiers}}",
+			args: map[string]any{"n": 2},
+			want: "2 fichiers",
+		},
+		{
+			name: "polish one",
+			tag:  language.Polish,
+			in:   "{n, plural, one {# plik} few {# pliki} many {# plików} other {# pliku}}",
+			args: map[string]any{"n": 1},
+			want: "1 plik",
+		},
+		{
+			name: "polish few",
+			tag:  language.Polish,
+			in:   "{n, plural, one {# plik} few {# pliki} many {# plików} other {# pliku}}",
+			args: map[string]any{"n": 2},
+			want: "2 pliki",
+		},
+		{
+			name: "polish many",
+			tag:  language.Polish,
+			in:   "{n, plural, one {# plik} few {# pliki} many {# plików} other {# pliku}}",
+			args: map[string]any{"n": 5},
+			want: "5 plików",
+		},
+		{
+			name: "polish few again at 22",
+			tag:  language.Polish,
+			in:   "{n, plural, one {# plik} few {# pliki} many {# plików} other {# pliku}}",
+			args: map[string]any{"n": 22},
+			want: "22 pliki",
+		},
+		{
+			name: "arabic zero",
+			tag:  language.Arabic,
+			in:   "{n, plural, zero {z} one {o} two {t} few {f} many {m} other {x}}",
+			args: map[string]any{"n": 0},
+			want: "z",
+		},
+		{
+			name: "arabic one",
+			tag:  language.Arabic,
+			in:   "{n, plural, zero {z} one {o} two {t} few {f} many {m} other {x}}",
+			args: map[string]any{"n": 1},
+			want: "o",
+		},
+		{
+			name: "arabic two",
+			tag:  language.Arabic,
+			in:   "{n, plural, zero {z} one {o} two {t} few {f} many {m} other {x}}",
+			args: map[string]any{"n": 2},
+			want: "t",
+		},
+		{
+			name: "arabic few",
+			tag:  language.Arabic,
+			in:   "{n, plural, zero {z} one {o} two {t} few {f} many {m} other {x}}",
+			args: map[string]any{"n": 3},
+			want: "f",
+		},
+		{
+			name: "arabic many",
+			tag:  language.Arabic,
+			in:   "{n, plural, zero {z} one {o} two {t} few {f} many {m} other {x}}",
+			args: map[string]any{"n": 11},
+			want: "m",
+		},
+		{
+			name: "arabic other",
+			tag:  language.Arabic,
+			in:   "{n, plural, zero {z} one {o} two {t} few {f} many {m} other {x}}",
+			args: map[string]any{"n": 100},
+			want: "x",
+		},
+		{
+			name: "exact match wins over category",
+			tag:  language.English,
+			in:   "{n, plural, =0 {none} one {# item} other {# items}}",
+			args: map[string]any{"n": 0},
+			want: "none",
+		},
+		{
+			name: "english one with pound",
+			tag:  language.English,
+			in:   "{n, plural, =0 {none} one {# item} other {# items}}",
+			args: map[string]any{"n": 1},
+			want: "1 item",
+		},
+		{
+			name: "float plural uses visible fraction digits",
+			tag:  language.English,
+			in:   "{n, plural, one {# day} other {# days}}",
+			args: map[string]any{"n": 1.5},
+			want: "1.5 days",
+		},
+		{
+			name: "string numeric value",
+			tag:  language.English,
+			in:   "{n, plural, one {# day} other {# days}}",
+			args: map[string]any{"n": "1"},
+			want: "1 day",
+		},
+		{
+			name: "non numeric plural uses other",
+			tag:  language.English,
+			in:   "{n, plural, one {x} other {# y}}",
+			args: map[string]any{"n": "abc"},
+			want: "abc y",
+		},
+		{
+			name: "missing plural argument",
+			tag:  language.English,
+			in:   "{n, plural, one {x} other {y}}",
+			args: nil,
+			want: "{n}",
+		},
+		{
+			name: "reordering",
+			tag:  language.French,
+			in:   "{b} avant {a}",
+			args: map[string]any{"a": "x", "b": "y"},
+			want: "y avant x",
+		},
+		{
+			name: "missing argument renders placeholder",
+			tag:  language.English,
+			in:   "Hello {a}",
+			args: nil,
+			want: "Hello {a}",
+		},
+		{
+			name: "select match",
+			tag:  language.English,
+			in:   "{g, select, female {she} other {they}}",
+			args: map[string]any{"g": "female"},
+			want: "she",
+		},
+		{
+			name: "select fallback",
+			tag:  language.English,
+			in:   "{g, select, female {she} other {they}}",
+			args: map[string]any{"g": "x"},
+			want: "they",
+		},
+		{
+			name: "select missing argument uses other",
+			tag:  language.English,
+			in:   "{g, select, female {she} other {they}}",
+			args: nil,
+			want: "they",
+		},
+		{
+			name: "tags kept",
+			tag:  language.English,
+			in:   "<b>{a}</b> and <link>x</link>",
+			args: map[string]any{"a": "y"},
+			want: "<b>y</b> and <link>x</link>",
+		},
+		{
+			name: "english number grouping",
+			tag:  language.English,
+			in:   "{n, number}",
+			args: map[string]any{"n": 1234567},
+			want: "1,234,567",
+		},
+		{
+			name: "date format",
+			tag:  language.English,
+			in:   "{d, date}",
+			args: map[string]any{"d": time.Date(2026, 10, 11, 9, 30, 0, 0, time.UTC)},
+			want: "2026-10-11",
+		},
+		{
+			name: "time format",
+			tag:  language.English,
+			in:   "{d, time}",
+			args: map[string]any{"d": time.Date(2026, 10, 11, 9, 30, 0, 0, time.UTC)},
+			want: "09:30",
+		},
+		{
+			name: "plain argument uses fmt",
+			tag:  language.English,
+			in:   "{a}",
+			args: map[string]any{"a": 42},
+			want: "42",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m, err := Parse(tt.in)
+			if err != nil {
+				t.Fatalf("Parse(%q): %v", tt.in, err)
+			}
+			if got := Format(m, tt.tag, tt.args); got != tt.want {
+				t.Fatalf("Format(%q) = %q, want %q", tt.in, got, tt.want)
+			}
+		})
+	}
+}
diff --git a/i18n/icu/parse.go b/i18n/icu/parse.go
new file mode 100644
index 000000000..19e4e4ad9
--- /dev/null
+++ b/i18n/icu/parse.go
@@ -0,0 +1,400 @@
+// Package icu parses and formats the ICU MessageFormat subset used by the
+// Gameplane language packs: simple arguments, number/date/time formats,
+// plural and select, tags for inline markup, and apostrophe quoting.
+package icu
+
+import (
+	"fmt"
+	"strings"
+)
+
+// Kind identifies the type of a parsed Node.
+type Kind int
+
+// Node kinds produced by Parse.
+const (
+	KindLiteral  Kind = iota // plain text
+	KindArgument             // {name} or {name, number|date|time[, style]}
+	KindPlural               // {name, plural, ...}
+	KindSelect               // {name, select, ...}
+	KindPound                // # inside a plural option
+	KindTag                  // <name>children</name>
+)
+
+// Node is one element of a parsed message.
+type Node struct {
+	Kind     Kind
+	Text     string   // literal text (unescaped)
+	Name     string   // argument name or tag name
+	Format   string   // "", "number", "date", "time" (KindArgument only)
+	Style    string   // optional style after second comma, trimmed
+	Options  []Option // plural/select branches, in source order
+	Children []Node   // tag body
+}
+
+// Option is one branch of a plural or select.
+type Option struct {
+	Key   string // "=3", "one", "other", or a select key
+	Value []Node
+}
+
+// Message is a parsed ICU message.
+type Message []Node
+
+// SyntaxError reports a malformed message at a byte offset.
+type SyntaxError struct {
+	Offset int
+	Msg    string
+}
+
+// Error implements error.
+func (e *SyntaxError) Error() string {
+	return fmt.Sprintf("offset %d: %s", e.Offset, e.Msg)
+}
+
+// ctx describes the lexical context in which a sequence is parsed.
+type ctx struct {
+	plural bool   // '#' is a pound inside the nearest enclosing plural
+	option bool   // inside a plural/select option; an unescaped '}' ends it
+	tag    string // inside a tag body; a closing tag ends it
+}
+
+type parser struct {
+	s   string
+	pos int
+}
+
+// Parse parses an ICU message. Errors are *SyntaxError values carrying the
+// byte offset of the problem.
+func Parse(s string) (Message, error) {
+	p := &parser{s: s}
+	msg, err := p.parseSeq(ctx{})
+	if err != nil {
+		return nil, err
+	}
+	if p.pos < len(p.s) {
+		return nil, p.errAt(p.pos, "unmatched '}'")
+	}
+	return msg, nil
+}
+
+func (p *parser) errAt(off int, msg string) error {
+	return &SyntaxError{Offset: off, Msg: msg}
+}
+
+func (p *parser) parseSeq(c ctx) (Message, error) {
+	var out []Node
+	var lit strings.Builder
+	flush := func() {
+		if lit.Len() > 0 {
+			out = append(out, Node{Kind: KindLiteral, Text: lit.String()})
+			lit.Reset()
+		}
+	}
+	for p.pos < len(p.s) {
+		ch := p.s[p.pos]
+		switch {
+		case ch == '\'':
+			p.apostrophe(c, &lit)
+		case ch == '{':
+			flush()
+			n, err := p.parseArgument(c)
+			if err != nil {
+				return nil, err
+			}
+			out = append(out, n)
+		case ch == '}':
+			if c.option {
+				flush()
+				return out, nil
+			}
+			return nil, p.errAt(p.pos, "unmatched '}'")
+		case ch == '#':
+			if c.plural {
+				flush()
+				out = append(out, Node{Kind: KindPound})
+			} else {
+				lit.WriteByte('#')
+			}
+			p.pos++
+		case ch == '<' && p.pos+1 < len(p.s) && p.s[p.pos+1] == '/':
+			if c.tag != "" {
+				flush()
+				return out, nil
+			}
+			return nil, p.errAt(p.pos, "closing tag has no matching opening tag")
+		case ch == '<' && p.pos+1 < len(p.s) && isLetter(p.s[p.pos+1]):
+			flush()
+			n, err := p.parseTag(c)
+			if err != nil {
+				return nil, err
+			}
+			out = append(out, n)
+		default:
+			lit.WriteByte(ch)
+			p.pos++
+		}
+	}
+	flush()
+	return out, nil
+}
+
+// apostrophe handles ICU apostrophe escaping. Two adjacent apostrophes are a
+// literal apostrophe. A quote before '{', '}', '<' or '|' (or '#' inside a plural) starts quoted
+// text that runs to the next lone apostrophe. Any other apostrophe is literal.
+func (p *parser) apostrophe(c ctx, lit *strings.Builder) {
+	next := byte(0)
+	if p.pos+1 < len(p.s) {
+		next = p.s[p.pos+1]
+	}
+	switch {
+	case next == '\'':
+		lit.WriteByte('\'')
+		p.pos += 2
+	case next == '{' || next == '}' || next == '<' || next == '|' || (next == '#' && c.plural):
+		p.pos++ // opening quote
+		for p.pos < len(p.s) {
+			b := p.s[p.pos]
+			if b == '\'' {
+				if p.pos+1 < len(p.s) && p.s[p.pos+1] == '\'' {
+					lit.WriteByte('\'')
+					p.pos += 2
+					continue
+				}
+				p.pos++ // closing quote
+				return
+			}
+			lit.WriteByte(b)
+			p.pos++
+		}
+	default:
+		lit.WriteByte('\'')
+		p.pos++
+	}
+}
+
+// parseArgument parses a brace expression starting at '{'.
+func (p *parser) parseArgument(c ctx) (Node, error) {
+	open := p.pos
+	p.pos++ // '{'
+	p.skipSpace()
+	name, ok := p.parseName(false)
+	if !ok {
+		return Node{}, p.errAt(p.pos, "expected argument name")
+	}
+	p.skipSpace()
+	if p.pos >= len(p.s) {
+		return Node{}, p.errAt(open, "unterminated '{'")
+	}
+	if p.s[p.pos] == '}' {
+		p.pos++
+		return Node{Kind: KindArgument, Name: name}, nil
+	}
+	if p.s[p.pos] != ',' {
+		return Node{}, p.errAt(p.pos, "expected ',' or '}' after argument name")
+	}
+	p.pos++
+	p.skipSpace()
+	typOff := p.pos
+	typ := p.parseWord()
+	p.skipSpace()
+	if p.pos >= len(p.s) {
+		return Node{}, p.errAt(open, "unterminated '{'")
+	}
+
+	switch typ {
+	case "number", "date", "time":
+		n := Node{Kind: KindArgument, Name: name, Format: typ}
+		if p.s[p.pos] == '}' {
+			p.pos++
+			return n, nil
+		}
+		if p.s[p.pos] != ',' {
+			return Node{}, p.errAt(p.pos, "expected ',' or '}' after format")
+		}
+		p.pos++
+		end := strings.IndexByte(p.s[p.pos:], '}')
+		if end < 0 {
+			return Node{}, p.errAt(open, "unterminated '{'")
+		}
+		n.Style = strings.TrimSpace(p.s[p.pos : p.pos+end])
+		p.pos += end + 1
+		return n, nil
+	case "plural", "select":
+		return p.parseChoice(c, name, typ, open)
+	case "":
+		return Node{}, p.errAt(typOff, "expected argument type")
+	default:
+		return Node{}, p.errAt(typOff, fmt.Sprintf("unknown argument type %q", typ))
+	}
+}
+
+// parseChoice parses the option list of a plural or select. p.pos is at the
+// comma that follows the type keyword.
+func (p *parser) parseChoice(c ctx, name, typ string, open int) (Node, error) {
+	if p.s[p.pos] != ',' {
+		return Node{}, p.errAt(p.pos, fmt.Sprintf("expected ',' after %s", typ))
+	}
+	p.pos++
+	n := Node{Kind: KindPlural, Name: name}
+	if typ == "select" {
+		n.Kind = KindSelect
+	}
+	seen := make(map[string]struct{})
+	for {
+		p.skipSpace()
+		if p.pos >= len(p.s) {
+			return Node{}, p.errAt(open, "unterminated '{'")
+		}
+		if p.s[p.pos] == '}' {
+			p.pos++
+			break
+		}
+		keyOff := p.pos
+		key, err := p.parseKey(typ)
+		if err != nil {
+			return Node{}, err
+		}
+		if _, dup := seen[key]; dup {
+			return Node{}, p.errAt(keyOff, fmt.Sprintf("duplicate key %q", key))
+		}
+		seen[key] = struct{}{}
+		p.skipSpace()
+		if p.pos >= len(p.s) {
+			return Node{}, p.errAt(open, "unterminated '{'")
+		}
+		if p.s[p.pos] != '{' {
+			return Node{}, p.errAt(p.pos, fmt.Sprintf("expected '{' after %q", key))
+		}
+		p.pos++
+		optCtx := ctx{plural: c.plural, option: true}
+		if typ == "plural" {
+			optCtx.plural = true
+		}
+		value, err := p.parseSeq(optCtx)
+		if err != nil {
+			return Node{}, err
+		}
+		if p.pos >= len(p.s) {
+			return Node{}, p.errAt(open, "unterminated '{'")
+		}
+		p.pos++ // closing '}' of the option
+		n.Options = append(n.Options, Option{Key: key, Value: value})
+	}
+	if _, ok := seen["other"]; !ok {
+		return Node{}, p.errAt(open, fmt.Sprintf("%s %q is missing other branch", typ, name))
+	}
+	return n, nil
+}
+
+// parseKey reads one option key: "=N" or a category for plural, a name
+// (letters, digits, '_' and '-') for select.
+func (p *parser) parseKey(typ string) (string, error) {
+	if typ == "select" {
+		key, ok := p.parseName(true)
+		if !ok {
+			return "", p.errAt(p.pos, "expected select key")
+		}
+		return key, nil
+	}
+	if p.pos < len(p.s) && p.s[p.pos] == '=' {
+		start := p.pos
+		p.pos++
+		digits := p.pos
+		for p.pos < len(p.s) && isDigit(p.s[p.pos]) {
+			p.pos++
+		}
+		if p.pos == digits {
+			return "", p.errAt(start, "expected digits after '='")
+		}
+		return p.s[start:p.pos], nil
+	}
+	off := p.pos
+	word := p.parseWord()
+	if word == "offset" {
+		return "", p.errAt(off, "offset: is not supported")
+	}
+	switch word {
+	case "zero", "one", "two", "few", "many", "other":
+		return word, nil
+	case "":
+		return "", p.errAt(off, "expected plural key")
+	default:
+		return "", p.errAt(off, fmt.Sprintf("unknown plural key %q", word))
+	}
+}
+
+// parseTag parses <name>body</name> starting at '<'.
+func (p *parser) parseTag(c ctx) (Node, error) {
+	open := p.pos
+	p.pos++ // '<'
+	name, _ := p.parseName(true)
+	if name == "" || !isLetter(name[0]) {
+		return Node{}, p.errAt(open, "invalid tag name")
+	}
+	if p.pos >= len(p.s) || p.s[p.pos] != '>' {
+		return Node{}, p.errAt(p.pos, fmt.Sprintf("tag <%s> must not have attributes", name))
+	}
+	p.pos++ // '>'
+	body, err := p.parseSeq(ctx{plural: c.plural, tag: name})
+	if err != nil {
+		return Node{}, err
+	}
+	if p.pos >= len(p.s) {
+		return Node{}, p.errAt(open, fmt.Sprintf("missing closing tag </%s>", name))
+	}
+	closeOff := p.pos
+	p.pos += 2 // "</"
+	closeName, _ := p.parseName(true)
+	if p.pos >= len(p.s) || p.s[p.pos] != '>' {
+		return Node{}, p.errAt(closeOff, "invalid closing tag")
+	}
+	p.pos++ // '>'
+	if closeName != name {
+		return Node{}, p.errAt(closeOff, fmt.Sprintf("closing tag </%s> does not match <%s>", closeName, name))
+	}
+	return Node{Kind: KindTag, Name: name, Children: body}, nil
+}
+
+// parseName reads an identifier: a letter or '_' followed by letters, digits,
+// '_' and, when dashes is true, '-'. Returns ok=false when none is present.
+func (p *parser) parseName(dashes bool) (string, bool) {
+	start := p.pos
+	if p.pos >= len(p.s) || (!isLetter(p.s[p.pos]) && p.s[p.pos] != '_') {
+		return "", false
+	}
+	p.pos++
+	for p.pos < len(p.s) {
+		b := p.s[p.pos]
+		if isLetter(b) || isDigit(b) || b == '_' || (dashes && b == '-') {
+			p.pos++
+			continue
+		}
+		break
+	}
+	return p.s[start:p.pos], true
+}
+
+// parseWord reads a run of ASCII letters (type keywords and plural categories).
+func (p *parser) parseWord() string {
+	start := p.pos
+	for p.pos < len(p.s) && isLetter(p.s[p.pos]) {
+		p.pos++
+	}
+	return p.s[start:p.pos]
+}
+
+func (p *parser) skipSpace() {
+	for p.pos < len(p.s) {
+		switch p.s[p.pos] {
+		case ' ', '\t', '\n', '\r':
+			p.pos++
+		default:
+			return
+		}
+	}
+}
+
+func isLetter(b byte) bool { return (b >= 'a' && b <= 'z') || (b >= 'A' && b <= 'Z') }
+
+func isDigit(b byte) bool { return b >= '0' && b <= '9' }
diff --git a/i18n/icu/parse_test.go b/i18n/icu/parse_test.go
new file mode 100644
index 000000000..8ab16ff1b
--- /dev/null
+++ b/i18n/icu/parse_test.go
@@ -0,0 +1,189 @@
+package icu
+
+import (
+	"errors"
+	"reflect"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+func TestParseValid(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		want Message
+	}{
+		{
+			name: "literal",
+			in:   "Hello world",
+			want: Message{{Kind: KindLiteral, Text: "Hello world"}},
+		},
+		{
+			name: "simple argument",
+			in:   "Hi {a}!",
+			want: Message{
+				{Kind: KindLiteral, Text: "Hi "},
+				{Kind: KindArgument, Name: "a"},
+				{Kind: KindLiteral, Text: "!"},
+			},
+		},
+		{
+			name: "number argument",
+			in:   "{n, number}",
+			want: Message{{Kind: KindArgument, Name: "n", Format: "number"}},
+		},
+		{
+			name: "date argument with style",
+			in:   "{d, date, short}",
+			want: Message{{Kind: KindArgument, Name: "d", Format: "date", Style: "short"}},
+		},
+		{
+			name: "plural with exact and category keys and pound",
+			in:   "{n, plural, =0 {none} one {# item} other {# items}}",
+			want: Message{{
+				Kind: KindPlural,
+				Name: "n",
+				Options: []Option{
+					{Key: "=0", Value: Message{{Kind: KindLiteral, Text: "none"}}},
+					{Key: "one", Value: Message{{Kind: KindPound}, {Kind: KindLiteral, Text: " item"}}},
+					{Key: "other", Value: Message{{Kind: KindPound}, {Kind: KindLiteral, Text: " items"}}},
+				},
+			}},
+		},
+		{
+			name: "select",
+			in:   "{g, select, male {he} other {they}}",
+			want: Message{{
+				Kind: KindSelect,
+				Name: "g",
+				Options: []Option{
+					{Key: "male", Value: Message{{Kind: KindLiteral, Text: "he"}}},
+					{Key: "other", Value: Message{{Kind: KindLiteral, Text: "they"}}},
+				},
+			}},
+		},
+		{
+			name: "nested select inside plural keeps pound",
+			in:   "{n, plural, other {{g, select, other {# x}}}}",
+			want: Message{{
+				Kind: KindPlural,
+				Name: "n",
+				Options: []Option{{
+					Key: "other",
+					Value: Message{{
+						Kind: KindSelect,
+						Name: "g",
+						Options: []Option{{
+							Key:   "other",
+							Value: Message{{Kind: KindPound}, {Kind: KindLiteral, Text: " x"}},
+						}},
+					}},
+				}},
+			}},
+		},
+		{
+			name: "pound outside plural is literal",
+			in:   "#1",
+			want: Message{{Kind: KindLiteral, Text: "#1"}},
+		},
+		{
+			name: "tag",
+			in:   "<b>x</b>",
+			want: Message{{Kind: KindTag, Name: "b", Children: Message{{Kind: KindLiteral, Text: "x"}}}},
+		},
+		{
+			name: "tag around argument",
+			in:   "<link>{a}</link>",
+			want: Message{{Kind: KindTag, Name: "link", Children: Message{{Kind: KindArgument, Name: "a"}}}},
+		},
+		{
+			name: "escaped apostrophe and quoted braces",
+			in:   "It''s '{literal}'",
+			want: Message{{Kind: KindLiteral, Text: "It's {literal}"}},
+		},
+		{
+			name: "lone apostrophe is literal",
+			in:   "don't",
+			want: Message{{Kind: KindLiteral, Text: "don't"}},
+		},
+		{
+			name: "unterminated quote runs to end",
+			in:   "'{x",
+			want: Message{{Kind: KindLiteral, Text: "{x"}},
+		},
+		{
+			name: "less-than not followed by letter is literal",
+			in:   "a < b",
+			want: Message{{Kind: KindLiteral, Text: "a < b"}},
+		},
+		{
+			name: "quoted tag-like text",
+			in:   "'<b>'",
+			want: Message{{Kind: KindLiteral, Text: "<b>"}},
+		},
+		{
+			name: "empty message",
+			in:   "",
+			want: nil,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := Parse(tt.in)
+			if err != nil {
+				t.Fatalf("Parse(%q) error: %v", tt.in, err)
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Fatalf("Parse(%q)\n got %#v\nwant %#v", tt.in, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestParseMalformed(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		msg  string
+	}{
+		{name: "lone open brace", in: "{", msg: "expected argument name"},
+		{name: "unterminated argument", in: "{a", msg: "unterminated '{'"},
+		{name: "unmatched close brace", in: "a}", msg: "unmatched '}'"},
+		{name: "plural without other", in: "{a, plural, one {x}}", msg: "missing other branch"},
+		{name: "unknown type", in: "{a, foo}", msg: "unknown argument type"},
+		{name: "unclosed tag", in: "<b>x", msg: "missing closing tag </b>"},
+		{name: "closing tag without open", in: "x</b>", msg: "closing tag has no matching opening tag"},
+		{name: "mismatched closing tag", in: "<b>x</i>", msg: "does not match"},
+		{name: "offset not supported", in: "{a, plural, offset:1 other {x}}", msg: "offset: is not supported"},
+		{name: "tag with attributes", in: `<b class="x">y</b>`, msg: "must not have attributes"},
+		{name: "duplicate key", in: "{a, select, x {1} x {2} other {3}}", msg: "duplicate key"},
+		{name: "unknown plural key", in: "{a, plural, mny {x} other {y}}", msg: "unknown plural key"},
+		{name: "missing option brace", in: "{a, select, x y other {z}}", msg: "expected '{'"},
+		{name: "unterminated style", in: "{d, date, short", msg: "unterminated '{'"},
+		{name: "unterminated option", in: "{a, select, other {x", msg: "unterminated '{'"},
+		{name: "empty equals key", in: "{a, plural, = {x} other {y}}", msg: "expected digits"},
+		{name: "unbalanced brace inside tag", in: "<b>x}</b>", msg: "unmatched '}'"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := Parse(tt.in)
+			if err == nil {
+				t.Fatalf("Parse(%q) succeeded, want error", tt.in)
+			}
+			var se *SyntaxError
+			if !errors.As(err, &se) {
+				t.Fatalf("Parse(%q) error %T is not *SyntaxError", tt.in, err)
+			}
+			if se.Offset < 0 || se.Offset > len(tt.in) {
+				t.Fatalf("Parse(%q) offset %d outside input", tt.in, se.Offset)
+			}
+			if !strings.Contains(se.Msg, tt.msg) {
+				t.Fatalf("Parse(%q) message %q does not contain %q", tt.in, se.Msg, tt.msg)
+			}
+			if got := se.Error(); got != "offset "+strconv.Itoa(se.Offset)+": "+se.Msg {
+				t.Fatalf("Error() = %q", got)
+			}
+		})
+	}
+}
diff --git a/i18n/icu/placeholders.go b/i18n/icu/placeholders.go
new file mode 100644
index 000000000..e9daf7bb2
--- /dev/null
+++ b/i18n/icu/placeholders.go
@@ -0,0 +1,58 @@
+package icu
+
+import "sort"
+
+// Arguments returns every argument name in m, including plural and select
+// names and names used inside options and tag children.
+func Arguments(m Message) map[string]struct{} {
+	set := make(map[string]struct{})
+	collectArguments(m, set)
+	return set
+}
+
+func collectArguments(nodes []Node, set map[string]struct{}) {
+	for _, n := range nodes {
+		switch n.Kind {
+		case KindArgument:
+			set[n.Name] = struct{}{}
+		case KindPlural, KindSelect:
+			set[n.Name] = struct{}{}
+			for _, o := range n.Options {
+				collectArguments(o.Value, set)
+			}
+		case KindTag:
+			collectArguments(n.Children, set)
+		}
+	}
+}
+
+// Tags returns every tag name in m, recursively.
+func Tags(m Message) map[string]struct{} {
+	set := make(map[string]struct{})
+	collectTags(m, set)
+	return set
+}
+
+func collectTags(nodes []Node, set map[string]struct{}) {
+	for _, n := range nodes {
+		switch n.Kind {
+		case KindTag:
+			set[n.Name] = struct{}{}
+			collectTags(n.Children, set)
+		case KindPlural, KindSelect:
+			for _, o := range n.Options {
+				collectTags(o.Value, set)
+			}
+		}
+	}
+}
+
+// SortedKeys returns the members of set in ascending order.
+func SortedKeys(set map[string]struct{}) []string {
+	keys := make([]string, 0, len(set))
+	for k := range set {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys
+}
diff --git a/i18n/icu/placeholders_test.go b/i18n/icu/placeholders_test.go
new file mode 100644
index 000000000..3081363f3
--- /dev/null
+++ b/i18n/icu/placeholders_test.go
@@ -0,0 +1,65 @@
+package icu
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestArguments(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		want []string
+	}{
+		{name: "simple", in: "{a} and {b}", want: []string{"a", "b"}},
+		{name: "plural name and nested option args", in: "{n, plural, one {{x}} other {# {y}}}", want: []string{"n", "x", "y"}},
+		{name: "select name and tag children", in: "{g, select, other {<b>{a}</b>}}", want: []string{"a", "g"}},
+		{name: "deeply nested", in: "{n, plural, other {{g, select, other {{deep}}}}}", want: []string{"deep", "g", "n"}},
+		{name: "none", in: "plain", want: []string{}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m, err := Parse(tt.in)
+			if err != nil {
+				t.Fatalf("Parse: %v", err)
+			}
+			got := SortedKeys(Arguments(m))
+			if !reflect.DeepEqual(got, tt.want) && (len(got) != 0 || len(tt.want) != 0) {
+				t.Fatalf("Arguments() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestTags(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		want []string
+	}{
+		{name: "single", in: "<b>x</b>", want: []string{"b"}},
+		{name: "nested", in: "<b><link>{a}</link></b>", want: []string{"b", "link"}},
+		{name: "inside plural option", in: "{n, plural, other {<b>#</b>}}", want: []string{"b"}},
+		{name: "none", in: "{a}", want: []string{}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m, err := Parse(tt.in)
+			if err != nil {
+				t.Fatalf("Parse: %v", err)
+			}
+			got := SortedKeys(Tags(m))
+			if !reflect.DeepEqual(got, tt.want) && (len(got) != 0 || len(tt.want) != 0) {
+				t.Fatalf("Tags() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestSortedKeys(t *testing.T) {
+	got := SortedKeys(map[string]struct{}{"c": {}, "a": {}, "b": {}})
+	want := []string{"a", "b", "c"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("SortedKeys = %v, want %v", got, want)
+	}
+}
diff --git a/i18n/locales/en/app.json b/i18n/locales/en/app.json
new file mode 100644
index 000000000..908c605fe
--- /dev/null
+++ b/i18n/locales/en/app.json
@@ -0,0 +1,874 @@
+{
+  "condition.addressassignment.addressinuse": {
+    "defaultMessage": "The requested address ''{address}'' is already in use by GameServer ''{server}''.",
+    "description": "AddressAssignment condition when another game server holds the requested address."
+  },
+  "condition.addressassignment.allocationfailed": {
+    "defaultMessage": "The address manager could not allocate an address: {detail}",
+    "description": "AddressAssignment condition when the address manager reports an allocation failure. detail is the address manager's own English message."
+  },
+  "condition.addressassignment.assigned": {
+    "defaultMessage": "{assignedFrom, select, pool {Address {address} assigned from pool ''{pool}''.} other {Address {address} assigned.}}",
+    "description": "AddressAssignment condition once an address is assigned. assignedFrom is pool or default."
+  },
+  "condition.addressassignment.assignmentpending": {
+    "defaultMessage": "Requested {requestKind, select, addressAndPool {address ''{address}'' from pool ''{pool}''} address {address ''{address}''} other {pool ''{pool}''}}: the address manager has not assigned an address yet.",
+    "description": "AddressAssignment condition while the address manager works."
+  },
+  "condition.addressassignment.ignoredforexposuremode": {
+    "defaultMessage": "Requested {requestKind, select, addressAndPool {address ''{address}'' from pool ''{pool}''} address {address ''{address}''} other {pool ''{pool}''}} is ignored: it applies only to the LoadBalancer expose mode, and this server is exposed as ''{expose}''.",
+    "description": "AddressAssignment condition when an address or pool is requested for a server that is not exposed as a LoadBalancer. expose is the current expose mode."
+  },
+  "condition.addressassignment.invalidaddress": {
+    "defaultMessage": "The requested address ''{address}'' is not a valid IP address.",
+    "description": "AddressAssignment condition when the requested address does not parse."
+  },
+  "condition.addressassignment.noaddressmanagerconfigured": {
+    "defaultMessage": "Requested {requestKind, select, addressAndPool {address ''{address}'' from pool ''{pool}''} address {address ''{address}''} other {pool ''{pool}''}} cannot be honored: this cluster has no load-balancer address manager configured, so any address comes from the default assignment policy.",
+    "description": "AddressAssignment condition when no address manager (MetalLB or Cilium) is configured."
+  },
+  "condition.addressassignment.poolnotfound": {
+    "defaultMessage": "The requested address pool ''{pool}'' was not found.",
+    "description": "AddressAssignment condition when the requested address pool does not exist."
+  },
+  "condition.addressassignment.servicenotready": {
+    "defaultMessage": "Requested {requestKind, select, addressAndPool {address ''{address}'' from pool ''{pool}''} address {address ''{address}''} other {pool ''{pool}''}}: waiting for the LoadBalancer Service that carries the request to exist.",
+    "description": "AddressAssignment condition before the load-balancer Service exists."
+  },
+  "condition.completed.failed": {
+    "defaultMessage": "The backup or restore failed.",
+    "description": "Completed condition on a Backup or Restore that failed. The message holds the English detail."
+  },
+  "condition.completed.jobfailed": {
+    "defaultMessage": "The backup job reported a failure.",
+    "description": "Completed condition on a Backup whose job failed."
+  },
+  "condition.completed.pending": {
+    "defaultMessage": "The backup is waiting to start.",
+    "description": "Completed condition on a Backup that has not started (dynamic: reason is the phase)."
+  },
+  "condition.completed.running": {
+    "defaultMessage": "The backup is running.",
+    "description": "Completed condition on a Backup in progress (dynamic: reason is the phase)."
+  },
+  "condition.completed.succeeded": {
+    "defaultMessage": "The backup or restore completed successfully.",
+    "description": "Completed condition on a Backup or Restore that finished."
+  },
+  "condition.datawipe.jobfailed": {
+    "defaultMessage": "The data wipe job did not complete. The volume may not be fully cleared.",
+    "description": "DataWipe condition when the wipe job fails."
+  },
+  "condition.failed.capture_already_in_progress": {
+    "defaultMessage": "Another capture is already running on this server.",
+    "description": "Failed condition when two captures target one server."
+  },
+  "condition.failed.failed": {
+    "defaultMessage": "The capture failed.",
+    "description": "Failed condition on a NetworkCapture; the message holds the English detail."
+  },
+  "condition.failed.podrestarted": {
+    "defaultMessage": "The game pod restarted while the capture was running.",
+    "description": "Failed condition when the pod was replaced during a capture."
+  },
+  "condition.failed.sidecarcrashed": {
+    "defaultMessage": "The capture sidecar exited unexpectedly.",
+    "description": "Failed condition when the capture container died."
+  },
+  "condition.filecleanupfailed.delete_failed": {
+    "defaultMessage": "Deleting the capture file failed. It may stay past its retention.",
+    "description": "Condition when the capture file could not be deleted."
+  },
+  "condition.healthy.agentfresh": {
+    "defaultMessage": "The agent is reporting heartbeats.",
+    "description": "Healthy condition while heartbeats arrive."
+  },
+  "condition.healthy.agentstale": {
+    "defaultMessage": "The agent has not reported a heartbeat recently.",
+    "description": "Healthy condition when heartbeats stopped."
+  },
+  "condition.healthy.badkubeconfig": {
+    "defaultMessage": "The kubeconfig could not be used.",
+    "description": "Healthy condition when the kubeconfig does not parse."
+  },
+  "condition.healthy.discoveryclientfailed": {
+    "defaultMessage": "Connecting to the cluster failed.",
+    "description": "Healthy condition when the discovery client cannot be built."
+  },
+  "condition.healthy.failed": {
+    "defaultMessage": "The server failed.",
+    "description": "Healthy condition when the server has failed."
+  },
+  "condition.healthy.healthcheckfailed": {
+    "defaultMessage": "The cluster health check failed.",
+    "description": "Healthy condition when the cluster does not answer."
+  },
+  "condition.healthy.healthcheckpassed": {
+    "defaultMessage": "The cluster is reachable and healthy.",
+    "description": "Healthy condition on a registered cluster."
+  },
+  "condition.healthy.idleasleep": {
+    "defaultMessage": "The server is asleep because no players are online.",
+    "description": "Healthy condition for an idle-sleeping server."
+  },
+  "condition.healthy.invalidsecret": {
+    "defaultMessage": "The kubeconfig secret is missing the required label.",
+    "description": "Healthy condition when the secret lacks the cluster-kubeconfig label."
+  },
+  "condition.healthy.missingkey": {
+    "defaultMessage": "The kubeconfig secret does not contain the expected key.",
+    "description": "Healthy condition when the kubeconfig key is absent."
+  },
+  "condition.healthy.namereserved": {
+    "defaultMessage": "The cluster name \"local\" is reserved.",
+    "description": "Healthy condition when a cluster is registered with the reserved name."
+  },
+  "condition.healthy.pending": {
+    "defaultMessage": "The server has not started yet.",
+    "description": "Healthy condition before the first start."
+  },
+  "condition.healthy.secretnotfound": {
+    "defaultMessage": "The kubeconfig secret was not found.",
+    "description": "Healthy condition when the kubeconfig secret is missing."
+  },
+  "condition.healthy.stopping": {
+    "defaultMessage": "The server is stopping.",
+    "description": "Healthy condition while stopping."
+  },
+  "condition.healthy.suspended": {
+    "defaultMessage": "The server is stopped.",
+    "description": "Healthy condition for a stopped server."
+  },
+  "condition.healthy.unknown": {
+    "defaultMessage": "The state of the server is not known yet.",
+    "description": "Healthy condition before the operator has observed the server."
+  },
+  "condition.idlescheduleinvalid.wakewindowunparseable": {
+    "defaultMessage": "A wake window in the idle schedule cannot be parsed: {details}",
+    "description": "Condition when spec.idle has an invalid wake window. details is the English parse error."
+  },
+  "condition.localesvalid.invalidentries": {
+    "defaultMessage": "Some module translation entries are invalid and were left out.",
+    "description": "LocalesValid condition on a GameTemplate when translation entries or files were dropped. The message holds the English per-language counts."
+  },
+  "condition.localesvalid.localestoolarge": {
+    "defaultMessage": "Some module translations were left out because they are too large.",
+    "description": "LocalesValid condition on a GameTemplate when a language file is over the size limit or the translations together exceed it. The message names the languages."
+  },
+  "condition.localesvalid.valid": {
+    "defaultMessage": "All module translations are valid.",
+    "description": "LocalesValid condition on a GameTemplate when every translation entry shipped with the module is valid."
+  },
+  "condition.localesvalid.writefailed": {
+    "defaultMessage": "Module translations could not be stored.",
+    "description": "LocalesValid condition on a GameTemplate when the translations ConfigMap could not be written. The message holds the English error."
+  },
+  "condition.progressing.containercreating": {
+    "defaultMessage": "Creating the container.",
+    "description": "Progressing detail while the kubelet creates the container."
+  },
+  "condition.progressing.containerexited": {
+    "defaultMessage": "The game container exited with code {exitCode} during startup. Check the logs.",
+    "description": "Progressing condition when the game container exits during startup. exitCode is the process exit code."
+  },
+  "condition.progressing.crashloopbackoff": {
+    "defaultMessage": "The game container keeps crashing during startup ({restartCount} restarts so far). Check the logs.",
+    "description": "Progressing condition when the game container crash-loops. restartCount is the number of restarts."
+  },
+  "condition.progressing.failed": {
+    "defaultMessage": "The server stopped trying to start.",
+    "description": "Progressing condition when startup has failed."
+  },
+  "condition.progressing.idleasleep": {
+    "defaultMessage": "The server is asleep because no players are online.",
+    "description": "Progressing condition for an idle-sleeping server."
+  },
+  "condition.progressing.imagepullfailed": {
+    "defaultMessage": "The game image cannot be pulled. Check the image reference.",
+    "description": "Progressing condition when the container image pull keeps failing."
+  },
+  "condition.progressing.installingserverfiles": {
+    "defaultMessage": "Downloading game files or waiting for the server to become ready.",
+    "description": "Progressing detail during first-run installation."
+  },
+  "condition.progressing.pending": {
+    "defaultMessage": "The server is waiting to be scheduled.",
+    "description": "Progressing condition while the pod is waiting for a node."
+  },
+  "condition.progressing.pullingimage": {
+    "defaultMessage": "Pulling the game image.",
+    "description": "Progressing detail while the container image downloads."
+  },
+  "condition.progressing.pvcprovisioningfailed": {
+    "defaultMessage": "Storage cannot be provisioned: PVC ''{pvc}'' needs StorageClass ''{storageClass}'', which does not exist on this cluster.",
+    "description": "Progressing condition when the data volume cannot be created. pvc is the volume claim name, storageClass the missing class."
+  },
+  "condition.progressing.stable": {
+    "defaultMessage": "The server is stable and nothing is changing.",
+    "description": "Progressing condition once the server is running."
+  },
+  "condition.progressing.starting": {
+    "defaultMessage": "The server is starting.",
+    "description": "Progressing condition while the pod starts."
+  },
+  "condition.progressing.stopping": {
+    "defaultMessage": "The server is stopping.",
+    "description": "Progressing condition while the pod stops."
+  },
+  "condition.progressing.suspended": {
+    "defaultMessage": "The server is stopped and nothing is in progress.",
+    "description": "Progressing condition for a stopped server."
+  },
+  "condition.progressing.unknown": {
+    "defaultMessage": "The state of the server is not known yet.",
+    "description": "Progressing condition before the operator has observed the server."
+  },
+  "condition.progressing.waitingforagent": {
+    "defaultMessage": "The server is up. Waiting for the first heartbeat from the agent.",
+    "description": "Progressing detail once the game container runs but the agent has not reported yet."
+  },
+  "condition.pulling.applied": {
+    "defaultMessage": "The module pull finished.",
+    "description": "Pulling condition once the template was applied."
+  },
+  "condition.pulling.applytemplate": {
+    "defaultMessage": "Applying the module template failed.",
+    "description": "Module condition when the GameTemplate cannot be written."
+  },
+  "condition.pulling.digestmismatch": {
+    "defaultMessage": "The module content does not match its pinned digest.",
+    "description": "Module condition when the digest differs from the pin."
+  },
+  "condition.pulling.incompatibleoperator": {
+    "defaultMessage": "The module needs a newer Gameplane operator.",
+    "description": "Module condition when gameplaneMinVersion is not met."
+  },
+  "condition.pulling.noversionavailable": {
+    "defaultMessage": "The module source has no available versions.",
+    "description": "Module condition when no version can be chosen."
+  },
+  "condition.pulling.pullfailed": {
+    "defaultMessage": "Pulling the module failed.",
+    "description": "Module condition when the OCI pull fails."
+  },
+  "condition.pulling.pulling": {
+    "defaultMessage": "Pulling the module.",
+    "description": "Pulling condition while a pull runs."
+  },
+  "condition.pulling.signatureinvalid": {
+    "defaultMessage": "The module signature could not be verified.",
+    "description": "Module condition when cosign verification fails."
+  },
+  "condition.pulling.sourceconfig": {
+    "defaultMessage": "The module source configuration is invalid.",
+    "description": "Module condition for a broken source setup."
+  },
+  "condition.pulling.sourcenotfound": {
+    "defaultMessage": "The module source was not found.",
+    "description": "Module condition when the named ModuleSource does not exist."
+  },
+  "condition.pulling.verifyconfig": {
+    "defaultMessage": "The signature verification settings are invalid.",
+    "description": "Module condition for a bad verification setup."
+  },
+  "condition.pulling.versionunavailable": {
+    "defaultMessage": "The requested version is not in the catalog.",
+    "description": "Module condition when the pinned version is missing."
+  },
+  "condition.pulling.waitingforcatalog": {
+    "defaultMessage": "Waiting for the module source to index this module.",
+    "description": "Module condition while the source has no catalog entry yet."
+  },
+  "condition.ready.applied": {
+    "defaultMessage": "The module template was applied.",
+    "description": "Ready condition on a Module after its GameTemplate was written."
+  },
+  "condition.ready.applytemplate": {
+    "defaultMessage": "Applying the module template failed.",
+    "description": "Module condition when the GameTemplate cannot be written."
+  },
+  "condition.ready.catalogpopulated": {
+    "defaultMessage": "The module catalog is populated.",
+    "description": "Ready condition on a source with a catalog."
+  },
+  "condition.ready.containerexited": {
+    "defaultMessage": "The game container exited with code {exitCode} during startup. Check the logs.",
+    "description": "Ready condition when the game container exits during startup. exitCode is the process exit code."
+  },
+  "condition.ready.crashloopbackoff": {
+    "defaultMessage": "The game container keeps crashing during startup ({restartCount} restarts so far). Check the logs.",
+    "description": "Ready condition when the game container crash-loops. restartCount is the number of restarts."
+  },
+  "condition.ready.digestmismatch": {
+    "defaultMessage": "The module content does not match its pinned digest.",
+    "description": "Module condition when the digest differs from the pin."
+  },
+  "condition.ready.failed": {
+    "defaultMessage": "{detail}",
+    "description": "Ready condition when the server cannot start. detail is the English reason from the operator, for example a missing template or an invalid configuration."
+  },
+  "condition.ready.idleasleep": {
+    "defaultMessage": "The server is asleep because no players are online.",
+    "description": "Ready condition for a server put to sleep by idle auto-sleep."
+  },
+  "condition.ready.imagepullfailed": {
+    "defaultMessage": "The game image cannot be pulled. Check the image reference.",
+    "description": "Ready condition when the container image pull keeps failing."
+  },
+  "condition.ready.incompatibleoperator": {
+    "defaultMessage": "The module needs a newer Gameplane operator.",
+    "description": "Module condition when gameplaneMinVersion is not met."
+  },
+  "condition.ready.inuse": {
+    "defaultMessage": "The module cannot be removed while game servers use its template.",
+    "description": "Ready condition when deletion is blocked."
+  },
+  "condition.ready.noversionavailable": {
+    "defaultMessage": "The module source has no available versions.",
+    "description": "Module condition when no version can be chosen."
+  },
+  "condition.ready.pending": {
+    "defaultMessage": "The server is waiting to start.",
+    "description": "Ready condition while the game server is being created."
+  },
+  "condition.ready.pullfailed": {
+    "defaultMessage": "Pulling the module failed.",
+    "description": "Module condition when the OCI pull fails."
+  },
+  "condition.ready.pvcprovisioningfailed": {
+    "defaultMessage": "Storage cannot be provisioned: PVC ''{pvc}'' needs StorageClass ''{storageClass}'', which does not exist on this cluster.",
+    "description": "Ready condition when the data volume cannot be created. pvc is the volume claim name, storageClass the missing class."
+  },
+  "condition.ready.running": {
+    "defaultMessage": "The server is running and the agent is reporting heartbeats.",
+    "description": "Ready condition while the game server is up."
+  },
+  "condition.ready.servingstalecatalog": {
+    "defaultMessage": "Serving the cached catalog. The last index attempt failed.",
+    "description": "Ready condition while an older catalog stays available."
+  },
+  "condition.ready.signatureinvalid": {
+    "defaultMessage": "The module signature could not be verified.",
+    "description": "Module condition when cosign verification fails."
+  },
+  "condition.ready.sourceconfig": {
+    "defaultMessage": "The module source configuration is invalid.",
+    "description": "Module condition for a broken source setup."
+  },
+  "condition.ready.sourcenotfound": {
+    "defaultMessage": "The module source was not found.",
+    "description": "Module condition when the named ModuleSource does not exist."
+  },
+  "condition.ready.sourceunreachable": {
+    "defaultMessage": "The module source has never been indexed successfully.",
+    "description": "Ready condition on a source that cannot be reached."
+  },
+  "condition.ready.starting": {
+    "defaultMessage": "The server is starting.",
+    "description": "Ready condition while the pod is starting up."
+  },
+  "condition.ready.stopping": {
+    "defaultMessage": "The server is stopping.",
+    "description": "Ready condition while the pod is shutting down."
+  },
+  "condition.ready.suspended": {
+    "defaultMessage": "The server is stopped.",
+    "description": "Ready condition for a server that was stopped."
+  },
+  "condition.ready.unknown": {
+    "defaultMessage": "The state of the server is not known yet.",
+    "description": "Ready condition before the operator has observed the server."
+  },
+  "condition.ready.verifyconfig": {
+    "defaultMessage": "The signature verification settings are invalid.",
+    "description": "Module condition for a bad verification setup."
+  },
+  "condition.ready.versionunavailable": {
+    "defaultMessage": "The requested version is not in the catalog.",
+    "description": "Module condition when the pinned version is missing."
+  },
+  "condition.ready.waitingforcatalog": {
+    "defaultMessage": "Waiting for the module source to index this module.",
+    "description": "Module condition while the source has no catalog entry yet."
+  },
+  "condition.retentionstopfailed.sidecar_stop_failed": {
+    "defaultMessage": "Stopping the capture sidecar at the end of retention failed.",
+    "description": "Condition when the retention-expiry stop failed."
+  },
+  "condition.retentiontrimmed.trimfailed": {
+    "defaultMessage": "Applying the retention policy failed.",
+    "description": "RetentionTrimmed condition when old backups could not be removed."
+  },
+  "condition.retentiontrimmed.trimsucceeded": {
+    "defaultMessage": "The retention policy was applied.",
+    "description": "RetentionTrimmed condition after a successful trim."
+  },
+  "condition.schedulevalid.cronparseerror": {
+    "defaultMessage": "The schedule is not a valid cron expression.",
+    "description": "ScheduleValid condition for an unparseable schedule."
+  },
+  "condition.schedulevalid.cronvalid": {
+    "defaultMessage": "The schedule is a valid cron expression.",
+    "description": "ScheduleValid condition for a good schedule."
+  },
+  "condition.sidecarstopfailed.sidecar_stop_failed": {
+    "defaultMessage": "Stopping the capture sidecar failed.",
+    "description": "Condition when the stop request to the sidecar failed."
+  },
+  "condition.sidecarstopped.never_started": {
+    "defaultMessage": "The capture was stopped before it started.",
+    "description": "SidecarStopped condition when a pending capture was cancelled."
+  },
+  "condition.sidecarstopped.stopped": {
+    "defaultMessage": "The capture sidecar was told to stop.",
+    "description": "SidecarStopped condition after a stop request."
+  },
+  "condition.snapshotforgotten.forgetabandoned": {
+    "defaultMessage": "The snapshot was not removed from the backup repository when the backup was deleted.",
+    "description": "SnapshotForgotten condition when the forget step was abandoned."
+  },
+  "condition.snapshotforgotten.forgotten": {
+    "defaultMessage": "The snapshot was removed from the backup repository.",
+    "description": "SnapshotForgotten condition after a deleted Backup's snapshot was forgotten."
+  },
+  "condition.synced.indexed": {
+    "defaultMessage": "The module source was indexed.",
+    "description": "Synced condition after a successful index."
+  },
+  "condition.synced.indexfailed": {
+    "defaultMessage": "Indexing the module source failed.",
+    "description": "Synced condition after a failed index."
+  },
+  "condition.tunneladdressinvalid.validationfailed": {
+    "defaultMessage": "Some tunnel endpoints were rejected: {details}",
+    "description": "Condition when endpoints reported by the playit tunnel pod fail validation. details is the English validation text."
+  },
+  "condition.tunnelhostnameignored.settingignored": {
+    "defaultMessage": "These settings apply to the backing Service, not to tunnel traffic: {settings}.",
+    "description": "Informational condition when hostname, source ranges or node ports are set on a server with a tunnel. settings is a comma-separated list of field names."
+  },
+  "condition.tunnelready.deploymentnotready": {
+    "defaultMessage": "Waiting for the tunnel deployment to become ready.",
+    "description": "TunnelReady condition while the tunnel pod is not ready."
+  },
+  "condition.tunnelready.invalidconfig": {
+    "defaultMessage": "{provider, select, none {The tunnel is enabled but the server has no tunnel configuration.} other {The ''{provider}'' tunnel provider is selected but its configuration is missing.}}",
+    "description": "TunnelReady condition for an incomplete tunnel setup. provider is the selected provider, or none."
+  },
+  "condition.tunnelready.nocredentials": {
+    "defaultMessage": "No credentials secret was provided, so the ''{provider}'' tunnel cannot authenticate.",
+    "description": "TunnelReady condition when a tunnel provider needs credentials that are missing."
+  },
+  "condition.tunnelready.portnotmapped": {
+    "defaultMessage": "No frp remote port is configured for: {ports}.",
+    "description": "TunnelReady condition for frp when advertised ports have no remote port. ports is a comma-separated list of port names."
+  },
+  "condition.tunnelready.ready": {
+    "defaultMessage": "{provider, select, playit {The tunnel deployment is ready. Waiting for the playit endpoint assignment.} tailscale {The tunnel deployment is ready and authenticated.} other {The tunnel deployment is ready and all ports are mapped.}}",
+    "description": "TunnelReady condition when the tunnel works."
+  },
+  "condition.tunnelready.tunnelcredentialrefused": {
+    "defaultMessage": "The tunnel credentials secret ''{secret}'' is not owned by this GameServer. {remedy, select, defaultName {Add an ownerReference to this GameServer to the Secret, or delete the Secret and save the credential again from the dashboard.} other {Save the credential from the dashboard, or add an ownerReference to this GameServer to the Secret.}}",
+    "description": "TunnelReady condition when the operator refuses to mount a credentials secret. secret is the secret name, remedy is defaultName or other."
+  },
+  "condition.tunnelready.unknownprovider": {
+    "defaultMessage": "Unknown tunnel provider ''{provider}''.",
+    "description": "TunnelReady condition when the provider name is not supported."
+  },
+  "condition.unquiesced.failed": {
+    "defaultMessage": "The server could not be resumed after the backup. Its world may still have auto-save turned off.",
+    "description": "Unquiesced condition when the unfreeze failed."
+  },
+  "condition.unquiesced.unquiesced": {
+    "defaultMessage": "The server was resumed after the backup.",
+    "description": "Unquiesced condition when the world was unfrozen."
+  },
+  "notify.detail.reason_message": {
+    "defaultMessage": "{reason} — {message}",
+    "description": "Body line that joins the Kubernetes reason and message of an event. The reason and message are quoted from Kubernetes in English and stay untranslated. The dash is an em dash."
+  },
+  "notify.detail.test": {
+    "defaultMessage": "This is a test notification from Gameplane. Your sink is wired up correctly.",
+    "description": "Body of a test notification sent from Admin Settings."
+  },
+  "notify.event.backup.failed": {
+    "defaultMessage": "backup failed",
+    "description": "Event name used inside a notification headline when a backup fails."
+  },
+  "notify.event.backup.succeeded": {
+    "defaultMessage": "backup succeeded",
+    "description": "Event name used inside a notification headline when a backup succeeds."
+  },
+  "notify.event.restore.failed": {
+    "defaultMessage": "restore failed",
+    "description": "Event name used inside a notification headline when a restore fails."
+  },
+  "notify.event.restore.succeeded": {
+    "defaultMessage": "restore succeeded",
+    "description": "Event name used inside a notification headline when a restore succeeds."
+  },
+  "notify.event.server.recovered": {
+    "defaultMessage": "server recovered",
+    "description": "Event name used inside a notification headline when a game server recovers."
+  },
+  "notify.event.server.unhealthy": {
+    "defaultMessage": "server unhealthy",
+    "description": "Event name used inside a notification headline when a game server becomes unhealthy."
+  },
+  "notify.event.test": {
+    "defaultMessage": "test notification",
+    "description": "Event name used inside the headline of a test notification."
+  },
+  "notify.title.named": {
+    "defaultMessage": "[{instance}] {event}: {namespace}/{name}",
+    "description": "Headline of a notification about a named resource. instance is the Gameplane instance name, event is the event name (for example \"backup failed\"), namespace and name identify the resource."
+  },
+  "notify.title.unnamed": {
+    "defaultMessage": "[{instance}] {event}",
+    "description": "Headline of a notification without a resource, such as a test send. instance is the Gameplane instance name, event is the event name."
+  },
+  "server.already_exists": {
+    "defaultMessage": "already exists",
+    "description": "API error when creating a resource whose name is already taken."
+  },
+  "server.auth.csrf_mismatch": {
+    "defaultMessage": "csrf mismatch",
+    "description": "API error from the session layer (sessions.go:Authenticate)."
+  },
+  "server.auth.invalid_credentials": {
+    "defaultMessage": "invalid credentials",
+    "description": "Login error. It is generic on purpose, so it never reveals whether an account exists."
+  },
+  "server.auth_providers.client_secret_required": {
+    "defaultMessage": "clientSecret is required",
+    "description": "API error from the auth provider credentials API (auth_provider_secret.go:put)."
+  },
+  "server.bad_request": {
+    "defaultMessage": "bad request",
+    "description": "API error for a malformed request that does not fit a more specific message."
+  },
+  "server.cluster_forbidden": {
+    "defaultMessage": "cluster not permitted",
+    "description": "API error when the ?cluster= query value names a cluster the caller may not use or that is unknown."
+  },
+  "server.common.invalid_json": {
+    "defaultMessage": "invalid json",
+    "description": "API error when a request body is not valid JSON."
+  },
+  "server.common.namespace_not_permitted": {
+    "defaultMessage": "namespace not permitted",
+    "description": "API error when the caller's role does not cover the requested namespace (400 form, returned by the permission check and the role-binding API)."
+  },
+  "server.common.too_many_requests": {
+    "defaultMessage": "too many requests",
+    "description": "API error when a signed-in user sends requests faster than the per-user rate limit allows; retry later."
+  },
+  "server.common.unauthenticated": {
+    "defaultMessage": "unauthenticated",
+    "description": "API error when a route that needs a signed-in user is called without a valid session."
+  },
+  "server.common.user_not_found": {
+    "defaultMessage": "user not found",
+    "description": "API error when the user named in the request does not exist."
+  },
+  "server.config.read_body": {
+    "defaultMessage": "read body",
+    "description": "API error from the admin config API (config.go:put)."
+  },
+  "server.config.unknown_section": {
+    "defaultMessage": "unknown section",
+    "description": "API error from the admin config API (config.go:put)."
+  },
+  "server.conflict_retry": {
+    "defaultMessage": "conflict, retry",
+    "description": "API error when a concurrent write changed the resource; the caller should re-read and retry."
+  },
+  "server.empty_body": {
+    "defaultMessage": "empty body",
+    "description": "API error when a route that expects a JSON body receives none."
+  },
+  "server.forbidden": {
+    "defaultMessage": "forbidden",
+    "description": "API error when the caller, or the API's service identity in Kubernetes, is not allowed to perform the operation."
+  },
+  "server.generic.400": {
+    "defaultMessage": "The request was not accepted.",
+    "description": "Generic sentence shown before the detail text for an HTTP 400 response."
+  },
+  "server.generic.401": {
+    "defaultMessage": "You are not signed in.",
+    "description": "Generic sentence shown before the detail text for an HTTP 401 response."
+  },
+  "server.generic.403": {
+    "defaultMessage": "You do not have permission to do this.",
+    "description": "Generic sentence shown before the detail text for an HTTP 403 response."
+  },
+  "server.generic.404": {
+    "defaultMessage": "The requested item was not found.",
+    "description": "Generic sentence shown before the detail text for an HTTP 404 response."
+  },
+  "server.generic.409": {
+    "defaultMessage": "The request conflicts with the current state.",
+    "description": "Generic sentence shown before the detail text for an HTTP 409 response."
+  },
+  "server.generic.413": {
+    "defaultMessage": "The request is too large.",
+    "description": "Generic sentence shown before the detail text for an HTTP 413 response."
+  },
+  "server.generic.415": {
+    "defaultMessage": "The request type is not supported.",
+    "description": "Generic sentence shown before the detail text for an HTTP 415 response."
+  },
+  "server.generic.422": {
+    "defaultMessage": "The request contains invalid values.",
+    "description": "Generic sentence shown before the detail text for an HTTP 422 response."
+  },
+  "server.generic.429": {
+    "defaultMessage": "Too many requests. Please wait and try again.",
+    "description": "Generic sentence shown before the detail text for an HTTP 429 response."
+  },
+  "server.generic.500": {
+    "defaultMessage": "The server hit an internal error.",
+    "description": "Generic sentence shown before the detail text for an HTTP 500 response."
+  },
+  "server.generic.501": {
+    "defaultMessage": "This is not supported here.",
+    "description": "Generic sentence shown before the detail text for an HTTP 501 response."
+  },
+  "server.generic.502": {
+    "defaultMessage": "An upstream service returned an error.",
+    "description": "Generic sentence shown before the detail text for an HTTP 502 response."
+  },
+  "server.generic.503": {
+    "defaultMessage": "The service is temporarily unavailable.",
+    "description": "Generic sentence shown before the detail text for an HTTP 503 response."
+  },
+  "server.i18n.unknown_language": {
+    "defaultMessage": "unknown language: {language}",
+    "description": "Shown when a user picks a language this release does not offer. language = the language tag that was sent."
+  },
+  "server.i18n.unlisted_language": {
+    "defaultMessage": "language is not available: {language}",
+    "description": "Shown when an admin picks an instance default language that is not offered (missing or below the completeness threshold). language = the tag."
+  },
+  "server.internal": {
+    "defaultMessage": "internal error",
+    "description": "API error for an unexpected server failure. The real error is logged on the server only."
+  },
+  "server.invalid": {
+    "defaultMessage": "{detail}",
+    "description": "API validation error. The argument detail is the validation message from Kubernetes, in English, and describes the caller's input."
+  },
+  "server.lifecycle.confirmation_mismatch": {
+    "defaultMessage": "confirmation does not match server name",
+    "description": "API error from the server lifecycle API (lifecycle.go:wipeDataHandler)."
+  },
+  "server.lifecycle.new_name_required": {
+    "defaultMessage": "newName required",
+    "description": "API error from the server lifecycle API (lifecycle.go:cloneHandler)."
+  },
+  "server.namespace_forbidden": {
+    "defaultMessage": "namespace not permitted",
+    "description": "API error when the user's role does not cover the requested namespace."
+  },
+  "server.not_found": {
+    "defaultMessage": "not found",
+    "description": "API error when the requested resource does not exist."
+  },
+  "server.notifications.sink_name_not_dns_label": {
+    "defaultMessage": "sink name must be a DNS label (lowercase, digits, hyphens)",
+    "description": "API error from the notification sinks API (notifications.go:deleteSecret, notifications.go:putSecret)."
+  },
+  "server.ownership.invalid_request": {
+    "defaultMessage": "invalid request",
+    "description": "API error from the server ownership API (ownership.go:setCollaborators)."
+  },
+  "server.ownership.user_id_required": {
+    "defaultMessage": "userId required",
+    "description": "API error from the server ownership API (ownership.go:transfer)."
+  },
+  "server.ownership.user_not_found_400": {
+    "defaultMessage": "user not found",
+    "description": "API error from the server ownership API (ownership.go:setCollaborators)."
+  },
+  "server.registry.api_key_required": {
+    "defaultMessage": "apiKey is required",
+    "description": "API error from the mod-registry credentials API (registry_secret.go:put)."
+  },
+  "server.remote_cluster_not_implemented": {
+    "defaultMessage": "not implemented: no cross-cluster agent yet; this route only serves the home cluster",
+    "description": "API response for a home-cluster-only route called with a ?cluster= value that names another cluster. No cross-cluster agent exists yet."
+  },
+  "server.roles.admin_not_editable": {
+    "defaultMessage": "the admin role cannot be edited",
+    "description": "API error from the roles API (roles.go:update)."
+  },
+  "server.roles.builtin_not_deletable": {
+    "defaultMessage": "built-in roles cannot be deleted",
+    "description": "API error from the roles API (roles.go:del)."
+  },
+  "server.roles.invalid_role_name": {
+    "defaultMessage": "invalid role name",
+    "description": "API error from the roles API (roles.go:create)."
+  },
+  "server.roles.remote_bindings_block_control_plane": {
+    "defaultMessage": "remove remote cluster-wide bindings before adding control-plane permissions",
+    "description": "API error from the roles API (roles.go:update)."
+  },
+  "server.roles.role_already_exists": {
+    "defaultMessage": "role already exists",
+    "description": "API error from the roles API (roles.go:create)."
+  },
+  "server.roles.role_in_use": {
+    "defaultMessage": "role is assigned to one or more users",
+    "description": "API error from the roles API (roles.go:del)."
+  },
+  "server.roles.role_not_found": {
+    "defaultMessage": "role not found",
+    "description": "API error from the roles API (roles.go:del, roles.go:update)."
+  },
+  "server.shares.expires_at_in_past": {
+    "defaultMessage": "expiresAt must be in the future",
+    "description": "API error from the share-links API (shares.go:createShareHandler)."
+  },
+  "server.shares.expiry_mutually_exclusive": {
+    "defaultMessage": "expiresAt and neverExpires are mutually exclusive",
+    "description": "API error from the share-links API (shares.go:createShareHandler)."
+  },
+  "server.shares.expiry_required": {
+    "defaultMessage": "must specify exactly one of expiresAt or neverExpires (or the deprecated expiresIn)",
+    "description": "API error from the share-links API (shares.go:createShareHandler)."
+  },
+  "server.shares.invalid_expires_at": {
+    "defaultMessage": "invalid expiresAt: must be RFC3339",
+    "description": "API error from the share-links API (shares.go:createShareHandler)."
+  },
+  "server.shares.invalid_expires_in": {
+    "defaultMessage": "invalid expiresIn",
+    "description": "API error from the share-links API (shares.go:createShareHandler)."
+  },
+  "server.telemetry.invalid_notice_action": {
+    "defaultMessage": "action must be one of seen|keep|extended-off|all-off",
+    "description": "API error from the telemetry API (telemetry.go:postNotice). Quoted words and tokens in the text are API keywords; keep them as written."
+  },
+  "server.telemetry.notice_not_pending": {
+    "defaultMessage": "telemetry notice is not pending",
+    "description": "API error from the telemetry API (telemetry.go:postNotice)."
+  },
+  "server.tunnel.credentials_in_use": {
+    "defaultMessage": "cannot delete tunnel credentials while tunnel is enabled; disable the tunnel first or use PUT to rotate credentials",
+    "description": "API error from the tunnel credentials API (tunnelcreds.go:delete)."
+  },
+  "server.tunnel.invalid_request_body": {
+    "defaultMessage": "invalid request body",
+    "description": "API error from the tunnel credentials API (tunnelcreds.go:put)."
+  },
+  "server.tunnel.secret_not_owned_conflict": {
+    "defaultMessage": "conflict: existing secret is not owned by this server",
+    "description": "API error from the tunnel credentials API (tunnelcreds.go:put)."
+  },
+  "server.tunnel.secret_not_owned_forbidden": {
+    "defaultMessage": "forbidden: cannot delete secret not owned by this server",
+    "description": "API error from the tunnel credentials API (tunnelcreds.go:delete)."
+  },
+  "server.unauthorized": {
+    "defaultMessage": "unauthorized",
+    "description": "API error when the request carries no valid credentials, or Kubernetes rejects the credentials used for the operation."
+  },
+  "server.users.appearance_mode_invalid": {
+    "defaultMessage": "appearanceMode must be \"light\", \"dark\" or \"system\"",
+    "description": "API error from the users API (users.go:putPreferences, users.go:resetPreferences). Quoted words and tokens in the text are API keywords; keep them as written."
+  },
+  "server.users.appearance_mode_required": {
+    "defaultMessage": "appearanceMode is required",
+    "description": "API error from the users API (users.go:putPreferences)."
+  },
+  "server.users.bad_id": {
+    "defaultMessage": "bad id",
+    "description": "API error from the users API (users.go:addBinding, users.go:del, users.go:deleteBinding, users.go:listBindings, users.go:resetPassword, users.go:update)."
+  },
+  "server.users.binding_already_exists": {
+    "defaultMessage": "binding already exists",
+    "description": "API error from the users API (users.go:addBinding)."
+  },
+  "server.users.binding_not_found": {
+    "defaultMessage": "binding not found",
+    "description": "API error from the users API (users.go:deleteBinding)."
+  },
+  "server.users.cannot_delete_last_manager": {
+    "defaultMessage": "cannot delete the last user who can manage users",
+    "description": "API error from the users API (users.go:del)."
+  },
+  "server.users.cannot_delete_self": {
+    "defaultMessage": "cannot delete self",
+    "description": "API error from the users API (users.go:del)."
+  },
+  "server.users.cannot_demote_last_manager": {
+    "defaultMessage": "cannot demote the last user who can manage users",
+    "description": "API error from the users API (users.go:update)."
+  },
+  "server.users.cannot_remove_own_management": {
+    "defaultMessage": "cannot remove your own user-management access",
+    "description": "API error from the users API (users.go:update)."
+  },
+  "server.users.cluster_role_is_primary": {
+    "defaultMessage": "the cluster-wide role is managed via the primary role",
+    "description": "API error from the users API (users.go:deleteBinding)."
+  },
+  "server.users.custom_accent_invalid": {
+    "defaultMessage": "customColors.accent must be a #RRGGBB hex color",
+    "description": "API error from the users API (users.go:putPreferences). Quoted words and tokens in the text are API keywords; keep them as written."
+  },
+  "server.users.custom_css_enabled_required": {
+    "defaultMessage": "customCssEnabled is required",
+    "description": "API error from the users API (users.go:putPreferences)."
+  },
+  "server.users.custom_surface_invalid": {
+    "defaultMessage": "customColors.surface must be a #RRGGBB hex color",
+    "description": "API error from the users API (users.go:putPreferences). Quoted words and tokens in the text are API keywords; keep them as written."
+  },
+  "server.users.invalid_email": {
+    "defaultMessage": "invalid email",
+    "description": "API error from the users API (users.go:create, users.go:update)."
+  },
+  "server.users.invalid_role": {
+    "defaultMessage": "invalid role",
+    "description": "API error from the users API (users.go:addBinding, users.go:create, users.go:update)."
+  },
+  "server.users.invalid_username": {
+    "defaultMessage": "invalid username",
+    "description": "API error from the users API (users.go:create)."
+  },
+  "server.users.password_too_short": {
+    "defaultMessage": "password too short",
+    "description": "API error from the users API (users.go:create, users.go:resetPassword)."
+  },
+  "server.users.preset_id_invalid": {
+    "defaultMessage": "presetId must be \"pink\" or \"legacy\"",
+    "description": "API error from the users API (users.go:putPreferences, users.go:resetPreferences). Quoted words and tokens in the text are API keywords; keep them as written."
+  },
+  "server.users.preset_id_required": {
+    "defaultMessage": "presetId is required",
+    "description": "API error from the users API (users.go:putPreferences)."
+  },
+  "server.users.remote_binding_not_removable": {
+    "defaultMessage": "remote control-plane bindings cannot be removed through supplemental grants",
+    "description": "API error from the users API (users.go:deleteBinding)."
+  },
+  "server.users.remote_role_scope_limited": {
+    "defaultMessage": "remote cluster-wide roles may grant only cluster:read and namespaced permissions",
+    "description": "API error from the users API (users.go:addBinding)."
+  },
+  "server.users.theme_type_invalid": {
+    "defaultMessage": "themeType must be \"preset\" or \"custom_colors\"",
+    "description": "API error from the users API (users.go:putPreferences). Quoted words and tokens in the text are API keywords; keep them as written."
+  },
+  "server.users.theme_type_required": {
+    "defaultMessage": "themeType is required",
+    "description": "API error from the users API (users.go:putPreferences)."
+  },
+  "server.ws.invalid_server_name": {
+    "defaultMessage": "invalid server name",
+    "description": "API error from the console and log WebSocket routes (attach.go:handle, podlogs.go:handle)."
+  }
+}
diff --git a/i18n/locales/en/meta.json b/i18n/locales/en/meta.json
new file mode 100644
index 000000000..59c7dbbb9
--- /dev/null
+++ b/i18n/locales/en/meta.json
@@ -0,0 +1,6 @@
+{
+  "tag": "en",
+  "nativeName": "English",
+  "englishName": "English",
+  "direction": "ltr"
+}
diff --git a/i18n/modlocale/ids.go b/i18n/modlocale/ids.go
new file mode 100644
index 000000000..6ed75bba4
--- /dev/null
+++ b/i18n/modlocale/ids.go
@@ -0,0 +1,250 @@
+// Package modlocale derives the translatable message ids of a game module from
+// its module.yaml and template.yaml. gp-module and the operator share it so
+// that authoring-time extraction and install-time validation agree on the id
+// set. Inputs are already-decoded documents, which keeps this package free of
+// any YAML dependency.
+package modlocale
+
+import (
+	"fmt"
+	"regexp"
+	"sort"
+	"strings"
+
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+)
+
+// Ref is one translatable string of a module.
+type Ref struct {
+	// ID is the message id, e.g. "config.MAX_PLAYERS.displayName".
+	ID string
+	// English is the source text, already ICU-escaped so it parses as a
+	// message with no placeholders.
+	English string
+	// Description is the translator note.
+	Description string
+}
+
+// Escape makes a user-controlled name safe to use as one dot-separated id
+// segment: "~" becomes "~0" and "." becomes "~1".
+func Escape(seg string) string {
+	return strings.ReplaceAll(strings.ReplaceAll(seg, "~", "~0"), ".", "~1")
+}
+
+// Unescape reverses Escape.
+func Unescape(seg string) string {
+	return strings.ReplaceAll(strings.ReplaceAll(seg, "~1", "."), "~0", "~")
+}
+
+// idRE is the module id rule: a fixed prefix (module, template, versions,
+// config, actions, mods, metrics) followed by dot-separated segments of
+// [A-Za-z0-9_~-]. Unlike dashboard and server ids (lower case only), module ids
+// may use upper case because they embed names from module.yaml and
+// template.yaml (for example MAX_PLAYERS).
+var idRE = regexp.MustCompile(`^(module|template|versions|config|actions|mods|metrics)(\.[A-Za-z0-9_~-]+)+$`)
+
+// ValidID reports whether id follows the module id rule: the prefixes above,
+// dot-separated segments of [A-Za-z0-9_~-], and "~" only as the reversible
+// escapes "~0" (a literal "~") and "~1" (a literal ".") produced by Escape.
+func ValidID(id string) bool {
+	if !idRE.MatchString(id) {
+		return false
+	}
+	for i := 0; i < len(id); i++ {
+		if id[i] != '~' {
+			continue
+		}
+		if i+1 >= len(id) || (id[i+1] != '0' && id[i+1] != '1') {
+			return false
+		}
+		i++
+	}
+	return true
+}
+
+// ICUEscape quotes plain text so that it parses as a literal ICU message:
+// apostrophes are doubled and runs containing "{", "}", "<" or "|" are quoted.
+func ICUEscape(s string) string {
+	isSpecial := func(r byte) bool { return r == '{' || r == '}' || r == '<' || r == '|' }
+	var b strings.Builder
+	for i := 0; i < len(s); {
+		c := s[i]
+		if !isSpecial(c) {
+			if c == '\'' {
+				// A run of apostrophes that leads into a special character is
+				// handled by the quoted-run branch below.
+				j := i
+				for j < len(s) && s[j] == '\'' {
+					j++
+				}
+				if j < len(s) && isSpecial(s[j]) {
+					i = quotedRun(&b, s, i)
+					continue
+				}
+				b.WriteString("''")
+				i++
+				continue
+			}
+			b.WriteByte(c)
+			i++
+			continue
+		}
+		i = quotedRun(&b, s, i)
+	}
+	return b.String()
+}
+
+// quotedRun writes the maximal run of special characters and apostrophes
+// starting at i as one quoted ICU section and returns the index after it.
+func quotedRun(b *strings.Builder, s string, i int) int {
+	j := i
+	for j < len(s) && (s[j] == '\'' || s[j] == '{' || s[j] == '}' || s[j] == '<' || s[j] == '|') {
+		j++
+	}
+	b.WriteByte('\'')
+	for _, c := range []byte(s[i:j]) {
+		if c == '\'' {
+			b.WriteString("''")
+			continue
+		}
+		b.WriteByte(c)
+	}
+	b.WriteByte('\'')
+	return j
+}
+
+// Derive returns every translatable string of a module, sorted by id. module
+// is the decoded module.yaml and template the decoded template.yaml (a full
+// GameTemplate document or just its spec). Empty fields produce no id.
+func Derive(module, template map[string]any) []Ref {
+	var refs []Ref
+	add := func(id, english, desc string) {
+		if english == "" {
+			return
+		}
+		refs = append(refs, Ref{ID: id, English: ICUEscape(english), Description: desc})
+	}
+
+	add("module.displayName", str(module, "displayName"), "Display name of the module (module.yaml displayName)")
+	add("module.summary", str(module, "summary"), "One-line summary of the module (module.yaml summary)")
+
+	spec := template
+	if s, ok := template["spec"].(map[string]any); ok {
+		spec = s
+	}
+	add("template.displayName", str(spec, "displayName"), "Display name of the game template (template.yaml spec.displayName)")
+	add("template.description", str(spec, "description"), "Description of the game template (template.yaml spec.description)")
+
+	for _, v := range list(spec, "versions") {
+		id := str(v, "id")
+		if id == "" {
+			continue
+		}
+		add("versions."+Escape(id)+".displayName", str(v, "displayName"),
+			fmt.Sprintf("Label of game version %s in the version picker (template.yaml spec.versions)", id))
+	}
+
+	for _, f := range list(spec, "configSchema") {
+		name := str(f, "name")
+		if name == "" {
+			continue
+		}
+		base := "config." + Escape(name)
+		add(base+".displayName", str(f, "displayName"),
+			fmt.Sprintf("Label of configuration field %s (template.yaml spec.configSchema)", name))
+		add(base+".description", str(f, "description"),
+			fmt.Sprintf("Help text of configuration field %s (template.yaml spec.configSchema)", name))
+		for _, opt := range strList(f, "enum") {
+			add(base+".options."+Escape(opt), opt,
+				fmt.Sprintf("Choice %q of configuration field %s (template.yaml spec.configSchema)", opt, name))
+		}
+	}
+
+	caps, _ := spec["capabilities"].(map[string]any)
+	for _, a := range list(caps, "actions") {
+		id := str(a, "id")
+		if id == "" {
+			continue
+		}
+		base := "actions." + Escape(id)
+		add(base+".displayName", str(a, "displayName"),
+			fmt.Sprintf("Label of server action %s (template.yaml spec.capabilities.actions)", id))
+		add(base+".description", str(a, "description"),
+			fmt.Sprintf("Help text of server action %s (template.yaml spec.capabilities.actions)", id))
+		add(base+".group", str(a, "group"),
+			fmt.Sprintf("Group heading of server action %s (template.yaml spec.capabilities.actions)", id))
+		for _, p := range list(a, "params") {
+			pname := str(p, "name")
+			if pname == "" {
+				continue
+			}
+			pbase := base + ".params." + Escape(pname)
+			add(pbase+".displayName", str(p, "displayName"),
+				fmt.Sprintf("Label of parameter %s of server action %s (template.yaml spec.capabilities.actions)", pname, id))
+			add(pbase+".description", str(p, "description"),
+				fmt.Sprintf("Help text of parameter %s of server action %s (template.yaml spec.capabilities.actions)", pname, id))
+			for _, opt := range strList(p, "enum") {
+				add(pbase+".options."+Escape(opt), opt,
+					fmt.Sprintf("Choice %q of parameter %s of server action %s (template.yaml spec.capabilities.actions)", opt, pname, id))
+			}
+		}
+	}
+
+	mods, _ := caps["mods"].(map[string]any)
+	if loaders, ok := mods["loaders"].(map[string]any); ok {
+		for key, raw := range loaders {
+			l, _ := raw.(map[string]any)
+			add("mods."+Escape(key)+".displayName", str(l, "displayName"),
+				fmt.Sprintf("Label of the mod volume %s in the Mods tab (template.yaml spec.capabilities.mods.loaders)", key))
+		}
+	}
+
+	status, _ := caps["status"].(map[string]any)
+	for _, m := range list(status, "metrics") {
+		id := str(m, "id")
+		if id == "" {
+			continue
+		}
+		add("metrics."+Escape(id)+".displayName", str(m, "displayName"),
+			fmt.Sprintf("Label of status metric %s (template.yaml spec.capabilities.status.metrics)", id))
+	}
+
+	sort.SliceStable(refs, func(i, j int) bool { return refs[i].ID < refs[j].ID })
+	return refs
+}
+
+// References turns Derive output into the English reference pack.
+func References(refs []Ref) map[string]pack.Entry {
+	out := make(map[string]pack.Entry, len(refs))
+	for _, r := range refs {
+		out[r.ID] = pack.Entry{DefaultMessage: r.English, Description: r.Description}
+	}
+	return out
+}
+
+func str(m map[string]any, key string) string {
+	s, _ := m[key].(string)
+	return s
+}
+
+func list(m map[string]any, key string) []map[string]any {
+	raw, _ := m[key].([]any)
+	out := make([]map[string]any, 0, len(raw))
+	for _, item := range raw {
+		if mm, ok := item.(map[string]any); ok {
+			out = append(out, mm)
+		}
+	}
+	return out
+}
+
+func strList(m map[string]any, key string) []string {
+	raw, _ := m[key].([]any)
+	out := make([]string, 0, len(raw))
+	for _, item := range raw {
+		if s, ok := item.(string); ok {
+			out = append(out, s)
+		}
+	}
+	return out
+}
diff --git a/i18n/modlocale/ids_test.go b/i18n/modlocale/ids_test.go
new file mode 100644
index 000000000..c27dcc356
--- /dev/null
+++ b/i18n/modlocale/ids_test.go
@@ -0,0 +1,305 @@
+package modlocale
+
+import (
+	"reflect"
+	"sort"
+	"strings"
+	"testing"
+
+	"github.com/GameplanePanel/gameplane/i18n/icu"
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+	"golang.org/x/text/language"
+)
+
+func TestEscapeVectors(t *testing.T) {
+	t.Parallel()
+	cases := []struct{ raw, escaped string }{
+		{"a.b", "a~1b"},
+		{"a~b", "a~0b"},
+		{"a~.b", "a~0~1b"},
+		{"~1", "~01"},
+		{"plain", "plain"},
+		{"", ""},
+	}
+	for _, c := range cases {
+		if got := Escape(c.raw); got != c.escaped {
+			t.Errorf("Escape(%q) = %q, want %q", c.raw, got, c.escaped)
+		}
+		if got := Unescape(c.escaped); got != c.raw {
+			t.Errorf("Unescape(%q) = %q, want %q", c.escaped, got, c.raw)
+		}
+	}
+}
+
+func TestEscapeRoundTrip(t *testing.T) {
+	t.Parallel()
+	alphabet := []string{".", "~", "0", "1", "a", "~0", "~1"}
+	var walk func(prefix string, depth int)
+	walk = func(prefix string, depth int) {
+		if got := Unescape(Escape(prefix)); got != prefix {
+			t.Fatalf("round trip of %q gave %q", prefix, got)
+		}
+		if strings.Contains(Escape(prefix), ".") {
+			t.Fatalf("Escape(%q) still contains a dot", prefix)
+		}
+		if depth == 0 {
+			return
+		}
+		for _, a := range alphabet {
+			walk(prefix+a, depth-1)
+		}
+	}
+	walk("", 4)
+}
+
+func TestICUEscapeParsesAsLiteral(t *testing.T) {
+	t.Parallel()
+	inputs := []string{
+		"plain text",
+		"Max players {20}",
+		"a < b | c > d",
+		"it's fine",
+		"''double''",
+		"'{",
+		"{'",
+		"{'{",
+		"{{}}",
+		"<b>bold</b>",
+		"trailing'",
+		"'",
+		"''",
+		"'|'",
+		"100% {x} 'quoted' <tag>",
+	}
+	for _, in := range inputs {
+		m, err := icu.Parse(ICUEscape(in))
+		if err != nil {
+			t.Errorf("ICUEscape(%q) = %q does not parse: %v", in, ICUEscape(in), err)
+			continue
+		}
+		if args := icu.Arguments(m); len(args) != 0 {
+			t.Errorf("ICUEscape(%q) has placeholders %v", in, args)
+		}
+		if tags := icu.Tags(m); len(tags) != 0 {
+			t.Errorf("ICUEscape(%q) has tags %v", in, tags)
+		}
+		if got := icu.Format(m, language.English, nil); got != in {
+			t.Errorf("ICUEscape(%q) formats back as %q", in, got)
+		}
+	}
+}
+
+func fixtureModule() map[string]any {
+	return map[string]any{"displayName": "Minecraft", "summary": "Run {Java} servers"}
+}
+
+func fixtureTemplate() map[string]any {
+	return map[string]any{
+		"apiVersion": "gameplane.io/v1alpha1",
+		"kind":       "GameTemplate",
+		"spec": map[string]any{
+			"displayName": "Minecraft Java",
+			"description": "Blocky game",
+			"versions": []any{
+				map[string]any{"id": "1.21.4", "displayName": "1.21.4 (Paper)", "image": "x"},
+				map[string]any{"id": "", "displayName": "ignored"},
+			},
+			"configSchema": []any{
+				map[string]any{
+					"name": "MAX_PLAYERS", "displayName": "Max players", "description": "How many {n}",
+					"type": "string", "default": "20",
+				},
+				map[string]any{
+					"name": "MODE", "displayName": "Mode",
+					"enum": []any{"survival", "creative", "a.b"},
+				},
+				map[string]any{"name": "NOLABEL"},
+			},
+			"capabilities": map[string]any{
+				"actions": []any{
+					map[string]any{
+						"id": "say", "displayName": "Say", "description": "Broadcast", "group": "Chat",
+						"command": "say {msg}",
+						"params": []any{
+							map[string]any{
+								"name": "msg", "displayName": "Message", "description": "Text",
+								"enum": []any{"hi", "bye"},
+							},
+						},
+					},
+				},
+				"mods": map[string]any{
+					"loaders": map[string]any{
+						"paper": map[string]any{"displayName": "Plugins", "path": "plugins"},
+						"bare":  map[string]any{"path": "mods"},
+					},
+				},
+				"status": map[string]any{
+					"metrics": []any{
+						map[string]any{"id": "tps", "displayName": "TPS", "command": "tps"},
+					},
+				},
+			},
+		},
+	}
+}
+
+func idsOf(refs []Ref) []string {
+	out := make([]string, len(refs))
+	for i, r := range refs {
+		out[i] = r.ID
+	}
+	return out
+}
+
+func TestDeriveCoversEveryRow(t *testing.T) {
+	t.Parallel()
+	refs := Derive(fixtureModule(), fixtureTemplate())
+	want := []string{
+		"actions.say.description",
+		"actions.say.displayName",
+		"actions.say.group",
+		"actions.say.params.msg.description",
+		"actions.say.params.msg.displayName",
+		"actions.say.params.msg.options.bye",
+		"actions.say.params.msg.options.hi",
+		"config.MAX_PLAYERS.description",
+		"config.MAX_PLAYERS.displayName",
+		"config.MODE.displayName",
+		"config.MODE.options.a~1b",
+		"config.MODE.options.creative",
+		"config.MODE.options.survival",
+		"metrics.tps.displayName",
+		"mods.paper.displayName",
+		"module.displayName",
+		"module.summary",
+		"template.description",
+		"template.displayName",
+		"versions.1~11~14.displayName",
+	}
+	// "1.21.4" escapes to "1~121~14"; recompute rather than hand-write it.
+	want[len(want)-1] = "versions." + Escape("1.21.4") + ".displayName"
+	sort.Strings(want)
+	if got := idsOf(refs); !reflect.DeepEqual(got, want) {
+		t.Fatalf("ids mismatch\n got: %v\nwant: %v", got, want)
+	}
+}
+
+func TestDeriveAcceptsBareSpec(t *testing.T) {
+	t.Parallel()
+	spec := fixtureTemplate()["spec"].(map[string]any)
+	a := idsOf(Derive(fixtureModule(), spec))
+	b := idsOf(Derive(fixtureModule(), fixtureTemplate()))
+	if !reflect.DeepEqual(a, b) {
+		t.Fatalf("bare spec and full document differ:\n%v\n%v", a, b)
+	}
+}
+
+func TestDeriveOmitsEmptyAndIsDeterministic(t *testing.T) {
+	t.Parallel()
+	refs := Derive(nil, map[string]any{})
+	if len(refs) != 0 {
+		t.Fatalf("expected no ids, got %v", idsOf(refs))
+	}
+	first := Derive(fixtureModule(), fixtureTemplate())
+	for range 20 {
+		if again := Derive(fixtureModule(), fixtureTemplate()); !reflect.DeepEqual(first, again) {
+			t.Fatal("Derive is not deterministic")
+		}
+	}
+	for _, r := range first {
+		if strings.Contains(r.ID, "NOLABEL") {
+			t.Errorf("field without labels produced id %s", r.ID)
+		}
+		if r.Description == "" {
+			t.Errorf("%s has no description", r.ID)
+		}
+	}
+}
+
+func TestDeriveEscapesEnglish(t *testing.T) {
+	t.Parallel()
+	refs := Derive(fixtureModule(), fixtureTemplate())
+	for _, r := range refs {
+		if r.ID == "module.summary" && r.English != "Run '{'Java'}' servers" {
+			t.Fatalf("summary English = %q", r.English)
+		}
+	}
+}
+
+func TestReferencesValidate(t *testing.T) {
+	t.Parallel()
+	ref := References(Derive(fixtureModule(), fixtureTemplate()))
+	if fs := pack.ValidateReference(ref, "en.json"); len(fs) != 0 {
+		t.Fatalf("derived reference is invalid: %v", fs)
+	}
+	if got := ref["module.displayName"].DefaultMessage; got != "Minecraft" {
+		t.Fatalf("module.displayName = %q", got)
+	}
+}
+
+func TestDeriveIgnoresMalformedShapes(t *testing.T) {
+	t.Parallel()
+	tmpl := map[string]any{
+		"spec": map[string]any{
+			"versions":     "not-a-list",
+			"configSchema": []any{"scalar", map[string]any{"name": 7}},
+			"capabilities": map[string]any{
+				"actions": []any{map[string]any{"displayName": "no id"}},
+				"mods":    map[string]any{"loaders": map[string]any{"x": "scalar"}},
+				"status":  map[string]any{"metrics": []any{map[string]any{"displayName": "no id"}}},
+			},
+		},
+	}
+	if refs := Derive(nil, tmpl); len(refs) != 0 {
+		t.Fatalf("expected no ids, got %v", idsOf(refs))
+	}
+}
+
+func TestValidIDAcceptsDerivedIDs(t *testing.T) {
+	t.Parallel()
+	for _, r := range Derive(fixtureModule(), fixtureTemplate()) {
+		if !ValidID(r.ID) {
+			t.Errorf("derived id %q fails ValidID", r.ID)
+		}
+	}
+}
+
+func TestValidIDVectors(t *testing.T) {
+	t.Parallel()
+	valid := []string{
+		"module.displayName",
+		"config.MAX_PLAYERS.displayName",
+		"config.a~1b.options.x~0y",
+		"versions.1-21~1x.displayName",
+	}
+	invalid := []string{
+		"config.a.b..c",
+		"Config.x",
+		"config.x~2",
+		"config.x~",
+		"config",
+		"unknown.x",
+		"config.has space",
+		"",
+	}
+	for _, id := range valid {
+		if !ValidID(id) {
+			t.Errorf("ValidID(%q) = false, want true", id)
+		}
+	}
+	for _, id := range invalid {
+		if ValidID(id) {
+			t.Errorf("ValidID(%q) = true, want false", id)
+		}
+	}
+}
+
+func TestEscapeRoundTripTildes(t *testing.T) {
+	t.Parallel()
+	for _, raw := range []string{"a~1b", "~~..", "~", ".", "~0.~1", "a.b~c"} {
+		if got := Unescape(Escape(raw)); got != raw {
+			t.Errorf("Unescape(Escape(%q)) = %q", raw, got)
+		}
+	}
+}
diff --git a/i18n/modlocale/ids_yaml_parity_test.go b/i18n/modlocale/ids_yaml_parity_test.go
new file mode 100644
index 000000000..4cba597f6
--- /dev/null
+++ b/i18n/modlocale/ids_yaml_parity_test.go
@@ -0,0 +1,56 @@
+package modlocale
+
+import (
+	"encoding/json"
+	"reflect"
+	"testing"
+
+	"gopkg.in/yaml.v3"
+)
+
+// The operator decodes YAML through a JSON round trip (sigs.k8s.io/yaml) while
+// gp-module and i18n-check use yaml.v3 directly. Derive must see the same ids
+// either way.
+func TestDeriveYAMLDecoderParity(t *testing.T) {
+	t.Parallel()
+	const moduleYAML = "displayName: Minecraft\nsummary: Java edition\n"
+	const templateYAML = `spec:
+  displayName: Minecraft
+  versions:
+    - id: "1.21"
+      displayName: "1.21 latest"
+  configSchema:
+    - name: MAX_PLAYERS
+      displayName: Max players
+      description: How many
+    - name: MODE
+      enum: [survival, creative]
+`
+	decode := func(src string) map[string]any {
+		var m map[string]any
+		if err := yaml.Unmarshal([]byte(src), &m); err != nil {
+			t.Fatal(err)
+		}
+		return m
+	}
+	roundTrip := func(m map[string]any) map[string]any {
+		raw, err := json.Marshal(m)
+		if err != nil {
+			t.Fatal(err)
+		}
+		var out map[string]any
+		if err := json.Unmarshal(raw, &out); err != nil {
+			t.Fatal(err)
+		}
+		return out
+	}
+	mod, tmpl := decode(moduleYAML), decode(templateYAML)
+	direct := Derive(mod, tmpl)
+	viaJSON := Derive(roundTrip(mod), roundTrip(tmpl))
+	if len(direct) == 0 {
+		t.Fatal("fixture derived no ids")
+	}
+	if !reflect.DeepEqual(direct, viaJSON) {
+		t.Fatalf("decoder mismatch:\n%v\n%v", direct, viaJSON)
+	}
+}
diff --git a/i18n/pack/completeness.go b/i18n/pack/completeness.go
new file mode 100644
index 000000000..2016e62b2
--- /dev/null
+++ b/i18n/pack/completeness.go
@@ -0,0 +1,102 @@
+package pack
+
+import "github.com/GameplanePanel/gameplane/i18n/icu"
+
+// Status is the state of one translated message.
+type Status string
+
+// Message statuses.
+const (
+	StatusTranslated  Status = "translated"
+	StatusNeedsReview Status = "needs-review"
+	StatusInvalid     Status = "invalid"
+	StatusMissing     Status = "missing"
+)
+
+// EntryStatus classifies a translation of ref. present reports whether the
+// translation pack has an entry for the id at all.
+func EntryStatus(ref Entry, tr Entry, present bool) Status {
+	if !present || tr.DefaultMessage == "" {
+		return StatusMissing
+	}
+	trM, err := icu.Parse(tr.DefaultMessage)
+	if err != nil {
+		return StatusInvalid
+	}
+	if refM, rerr := icu.Parse(ref.DefaultMessage); rerr == nil {
+		if !sameSet(icu.Arguments(refM), icu.Arguments(trM)) {
+			return StatusInvalid
+		}
+	}
+	if CheckMarkup(tr.DefaultMessage, trM) != "" {
+		return StatusInvalid
+	}
+	if tr.SourceHash != "" && tr.SourceHash != SourceHash(ref.DefaultMessage) {
+		return StatusNeedsReview
+	}
+	return StatusTranslated
+}
+
+// Statuses returns the status of every reference id in tr.
+func Statuses(ref, tr map[string]Entry) map[string]Status {
+	out := make(map[string]Status, len(ref))
+	for id, refE := range ref {
+		e, ok := tr[id]
+		out[id] = EntryStatus(refE, e, ok)
+	}
+	return out
+}
+
+// Completeness returns the percentage of reference ids that have a usable
+// translation (translated or needs-review). An empty reference is 100.
+func Completeness(ref, tr map[string]Entry) float64 {
+	if len(ref) == 0 {
+		return 100
+	}
+	usable := 0
+	for _, st := range Statuses(ref, tr) {
+		if st == StatusTranslated || st == StatusNeedsReview {
+			usable++
+		}
+	}
+	return float64(usable) * 100 / float64(len(ref))
+}
+
+// Listed reports whether a language is offered to users. English is always
+// listed; others need enough completeness, left-to-right text, and must not be
+// the pseudo-locale.
+func Listed(tag string, meta Meta, completeness float64) bool {
+	if tag == "en" {
+		return true
+	}
+	return completeness >= ListingThreshold && meta.Direction == "ltr" && tag != "en-XA"
+}
+
+// Valid returns the entries of tr that may be shown to users: ids the
+// reference still has, with status translated or needs-review.
+func Valid(ref, tr map[string]Entry) map[string]Entry {
+	out := make(map[string]Entry, len(tr))
+	for id, e := range tr {
+		refE, ok := ref[id]
+		if !ok {
+			continue
+		}
+		switch EntryStatus(refE, e, true) {
+		case StatusTranslated, StatusNeedsReview:
+			out[id] = e
+		}
+	}
+	return out
+}
+
+func sameSet(a, b map[string]struct{}) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for k := range a {
+		if _, ok := b[k]; !ok {
+			return false
+		}
+	}
+	return true
+}
diff --git a/i18n/pack/completeness_test.go b/i18n/pack/completeness_test.go
new file mode 100644
index 000000000..36f184183
--- /dev/null
+++ b/i18n/pack/completeness_test.go
@@ -0,0 +1,114 @@
+package pack
+
+import "testing"
+
+func TestEntryStatus(t *testing.T) {
+	ref := Entry{DefaultMessage: "Hi {name}", Description: "greet"}
+	tests := []struct {
+		name    string
+		tr      Entry
+		present bool
+		want    Status
+	}{
+		{name: "absent", present: false, want: StatusMissing},
+		{name: "empty message", tr: Entry{}, present: true, want: StatusMissing},
+		{name: "bad syntax", tr: Entry{DefaultMessage: "Salut {name"}, present: true, want: StatusInvalid},
+		{name: "placeholder mismatch", tr: Entry{DefaultMessage: "Salut"}, present: true, want: StatusInvalid},
+		{name: "markup problem", tr: Entry{DefaultMessage: "<i>Salut {name}</i>"}, present: true, want: StatusInvalid},
+		{name: "stale", tr: Entry{DefaultMessage: "Salut {name}", SourceHash: "000000000000"}, present: true, want: StatusNeedsReview},
+		{name: "current hash", tr: Entry{DefaultMessage: "Salut {name}", SourceHash: SourceHash(ref.DefaultMessage)}, present: true, want: StatusTranslated},
+		{name: "translated", tr: Entry{DefaultMessage: "Salut {name}"}, present: true, want: StatusTranslated},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := EntryStatus(ref, tt.tr, tt.present); got != tt.want {
+				t.Fatalf("EntryStatus = %s, want %s", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestStatusesAndCompleteness(t *testing.T) {
+	ref := map[string]Entry{
+		"a": {DefaultMessage: "A", Description: "d"},
+		"b": {DefaultMessage: "B", Description: "d"},
+	}
+	if got := Completeness(ref, nil); got != 0 {
+		t.Fatalf("Completeness empty translation = %v, want 0", got)
+	}
+	half := map[string]Entry{"a": {DefaultMessage: "AA"}}
+	if got := Completeness(ref, half); got != 50 {
+		t.Fatalf("Completeness half = %v, want 50", got)
+	}
+	stale := map[string]Entry{
+		"a": {DefaultMessage: "AA"},
+		"b": {DefaultMessage: "BB", SourceHash: "000000000000"},
+	}
+	if got := Completeness(ref, stale); got != 100 {
+		t.Fatalf("Completeness with needs-review = %v, want 100", got)
+	}
+	st := Statuses(ref, half)
+	if st["a"] != StatusTranslated || st["b"] != StatusMissing {
+		t.Fatalf("Statuses = %v", st)
+	}
+	if got := Completeness(map[string]Entry{}, nil); got != 100 {
+		t.Fatalf("Completeness empty reference = %v, want 100", got)
+	}
+}
+
+func TestListed(t *testing.T) {
+	ltr := Meta{Direction: "ltr"}
+	rtl := Meta{Direction: "rtl"}
+	tests := []struct {
+		name string
+		tag  string
+		meta Meta
+		pct  float64
+		want bool
+	}{
+		{name: "english always", tag: "en", meta: Meta{}, pct: 0, want: true},
+		{name: "just below", tag: "fr", meta: ltr, pct: 79.9, want: false},
+		{name: "at threshold", tag: "fr", meta: ltr, pct: 80, want: true},
+		{name: "complete", tag: "fr", meta: ltr, pct: 100, want: true},
+		{name: "rtl excluded", tag: "ar", meta: rtl, pct: 100, want: false},
+		{name: "pseudo locale excluded", tag: "en-XA", meta: ltr, pct: 100, want: false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := Listed(tt.tag, tt.meta, tt.pct); got != tt.want {
+				t.Fatalf("Listed = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestValidDropsInvalidEntries(t *testing.T) {
+	ref := map[string]Entry{
+		"ok":      {DefaultMessage: "Hi {n}", Description: "d"},
+		"bad":     {DefaultMessage: "Hi", Description: "d"},
+		"stale":   {DefaultMessage: "Yo", Description: "d"},
+		"missing": {DefaultMessage: "Miss", Description: "d"},
+	}
+	tr := map[string]Entry{
+		"ok":      {DefaultMessage: "Salut {n}"},
+		"bad":     {DefaultMessage: "Salut {n}"},
+		"stale":   {DefaultMessage: "Salut", SourceHash: "000000000000"},
+		"unknown": {DefaultMessage: "Nope"},
+	}
+	got := Valid(ref, tr)
+	if _, ok := got["ok"]; !ok {
+		t.Error("ok dropped")
+	}
+	if _, ok := got["stale"]; !ok {
+		t.Error("needs-review entry dropped")
+	}
+	if _, ok := got["bad"]; ok {
+		t.Error("placeholder-mismatched entry kept")
+	}
+	if _, ok := got["unknown"]; ok {
+		t.Error("id not in reference kept")
+	}
+	if len(got) != 2 {
+		t.Fatalf("Valid returned %d entries, want 2", len(got))
+	}
+}
diff --git a/i18n/pack/pack.go b/i18n/pack/pack.go
new file mode 100644
index 000000000..19a0dd669
--- /dev/null
+++ b/i18n/pack/pack.go
@@ -0,0 +1,119 @@
+// Package pack reads, writes and validates language pack files: the per-language
+// app.json entry maps, their meta.json descriptors, and the English reference
+// that translators work from.
+package pack
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"regexp"
+)
+
+// ListingThreshold is the minimum completeness percentage at which a
+// translation is offered to users.
+const ListingThreshold = 80.0
+
+// Entry is one message in an app.json pack.
+type Entry struct {
+	DefaultMessage string `json:"defaultMessage"`
+	Description    string `json:"description,omitempty"`
+	SourceHash     string `json:"sourceHash,omitempty"`
+}
+
+// Credit names a contributor of a translation.
+type Credit struct {
+	Name string `json:"name"`
+	URL  string `json:"url,omitempty"`
+}
+
+// Meta describes a language pack in meta.json.
+type Meta struct {
+	Tag         string   `json:"tag"`
+	NativeName  string   `json:"nativeName"`
+	EnglishName string   `json:"englishName"`
+	Direction   string   `json:"direction"`
+	Credits     []Credit `json:"credits,omitempty"`
+}
+
+var tagRE = regexp.MustCompile(`^[a-z]{2,3}(-[A-Z][a-z]{3})?(-([A-Z]{2}|[0-9]{3}))?$`)
+
+// ValidTag reports whether tag is a well-formed BCP 47 language tag in the
+// subset Gameplane accepts (language, optional script, optional region).
+func ValidTag(tag string) bool {
+	return tagRE.MatchString(tag)
+}
+
+// ParseEntries decodes an app.json file. The top level must be a JSON object
+// whose values are entry objects; unknown entry keys are rejected.
+func ParseEntries(data []byte) (map[string]Entry, error) {
+	var raw map[string]json.RawMessage
+	if err := json.Unmarshal(data, &raw); err != nil {
+		return nil, fmt.Errorf("pack: parse entries: %w", err)
+	}
+	if raw == nil {
+		return nil, errors.New("pack: parse entries: top level must be a JSON object")
+	}
+	out := make(map[string]Entry, len(raw))
+	for id, msg := range raw {
+		dec := json.NewDecoder(bytes.NewReader(msg))
+		dec.DisallowUnknownFields()
+		var e Entry
+		if err := dec.Decode(&e); err != nil {
+			return nil, fmt.Errorf("pack: entry %q: %w", id, err)
+		}
+		if err := expectEOF(dec); err != nil {
+			return nil, fmt.Errorf("pack: entry %q: %w", id, err)
+		}
+		if e.DefaultMessage == "" {
+			return nil, fmt.Errorf("pack: entry %q has no defaultMessage", id)
+		}
+		out[id] = e
+	}
+	return out, nil
+}
+
+// ParseMeta decodes a meta.json file, rejecting unknown keys and trailing data.
+func ParseMeta(data []byte) (Meta, error) {
+	dec := json.NewDecoder(bytes.NewReader(data))
+	dec.DisallowUnknownFields()
+	var m Meta
+	if err := dec.Decode(&m); err != nil {
+		return Meta{}, fmt.Errorf("pack: parse meta: %w", err)
+	}
+	if err := expectEOF(dec); err != nil {
+		return Meta{}, fmt.Errorf("pack: parse meta: %w", err)
+	}
+	return m, nil
+}
+
+func expectEOF(dec *json.Decoder) error {
+	if _, err := dec.Token(); !errors.Is(err, io.EOF) {
+		return errors.New("unexpected data after JSON value")
+	}
+	return nil
+}
+
+// Marshal encodes entries as app.json: keys sorted, two-space indentation,
+// HTML characters left unescaped, and a trailing newline.
+func Marshal(entries map[string]Entry) ([]byte, error) {
+	var buf bytes.Buffer
+	enc := json.NewEncoder(&buf)
+	enc.SetEscapeHTML(false)
+	enc.SetIndent("", "  ")
+	if err := enc.Encode(entries); err != nil {
+		return nil, fmt.Errorf("pack: marshal entries: %w", err)
+	}
+	return buf.Bytes(), nil
+}
+
+// SourceHash returns the first 12 hex characters of the SHA-256 of the English
+// message. It records which English text a translation was made from.
+func SourceHash(english string) string {
+	sum := sha256.Sum256([]byte(english))
+	return hex.EncodeToString(sum[:])[:12]
+}
diff --git a/i18n/pack/pack_test.go b/i18n/pack/pack_test.go
new file mode 100644
index 000000000..eeb8c6d02
--- /dev/null
+++ b/i18n/pack/pack_test.go
@@ -0,0 +1,137 @@
+package pack
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+
+	"github.com/GameplanePanel/gameplane/i18n/icu"
+)
+
+func TestParseEntries(t *testing.T) {
+	tests := []struct {
+		name    string
+		in      string
+		wantErr bool
+		wantLen int
+	}{
+		{name: "valid", in: `{"a":{"defaultMessage":"Hi","description":"greet"}}`, wantLen: 1},
+		{name: "empty object", in: `{}`, wantLen: 0},
+		{name: "null top level", in: `null`, wantErr: true},
+		{name: "array top level", in: `[]`, wantErr: true},
+		{name: "unknown key", in: `{"a":{"defaultMessage":"x","extra":1}}`, wantErr: true},
+		{name: "missing defaultMessage", in: `{"a":{"description":"x"}}`, wantErr: true},
+		{name: "null entry", in: `{"a":null}`, wantErr: true},
+		{name: "trailing data", in: `{} {}`, wantErr: true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ParseEntries([]byte(tt.in))
+			if (err != nil) != tt.wantErr {
+				t.Fatalf("ParseEntries err = %v, wantErr %v", err, tt.wantErr)
+			}
+			if err == nil && len(got) != tt.wantLen {
+				t.Fatalf("len = %d, want %d", len(got), tt.wantLen)
+			}
+		})
+	}
+}
+
+func TestParseMeta(t *testing.T) {
+	good := `{"tag":"fr","nativeName":"Français","englishName":"French","direction":"ltr","credits":[{"name":"A"}]}`
+	m, err := ParseMeta([]byte(good))
+	if err != nil {
+		t.Fatalf("ParseMeta: %v", err)
+	}
+	if m.Tag != "fr" || len(m.Credits) != 1 {
+		t.Fatalf("unexpected meta %+v", m)
+	}
+	for name, in := range map[string]string{
+		"unknown key":   `{"tag":"fr","bogus":1}`,
+		"trailing data": good + ` {}`,
+		"not an object": `"fr"`,
+	} {
+		if _, err := ParseMeta([]byte(in)); err == nil {
+			t.Errorf("%s: expected error", name)
+		}
+	}
+}
+
+func TestMarshalRoundTripIsByteExact(t *testing.T) {
+	data := []byte("{\n  \"a\": {\n    \"defaultMessage\": \"<b>Hi</b> & more\",\n    \"description\": \"greet\"\n  },\n  \"b\": {\n    \"defaultMessage\": \"Bye\",\n    \"description\": \"farewell\",\n    \"sourceHash\": \"0123456789ab\"\n  }\n}\n")
+	entries, err := ParseEntries(data)
+	if err != nil {
+		t.Fatalf("ParseEntries: %v", err)
+	}
+	out, err := Marshal(entries)
+	if err != nil {
+		t.Fatalf("Marshal: %v", err)
+	}
+	if !bytes.Equal(out, data) {
+		t.Fatalf("round trip differs:\n%s\nwant:\n%s", out, data)
+	}
+}
+
+func TestMarshalSortsKeysAndEmptyMap(t *testing.T) {
+	out, err := Marshal(map[string]Entry{
+		"z": {DefaultMessage: "Z"},
+		"a": {DefaultMessage: "A"},
+	})
+	if err != nil {
+		t.Fatalf("Marshal: %v", err)
+	}
+	if want := "{\n  \"a\": {\n    \"defaultMessage\": \"A\"\n  },\n  \"z\": {\n    \"defaultMessage\": \"Z\"\n  }\n}\n"; string(out) != want {
+		t.Fatalf("got %q, want %q", out, want)
+	}
+	empty, err := Marshal(map[string]Entry{})
+	if err != nil {
+		t.Fatalf("Marshal empty: %v", err)
+	}
+	if string(empty) != "{}\n" {
+		t.Fatalf("empty = %q, want {}\\n", empty)
+	}
+}
+
+func TestSourceHash(t *testing.T) {
+	h := SourceHash("Hello")
+	if len(h) != 12 {
+		t.Fatalf("len = %d, want 12", len(h))
+	}
+	if h != SourceHash("Hello") {
+		t.Fatal("SourceHash is not stable")
+	}
+	if h == SourceHash("Hello!") {
+		t.Fatal("SourceHash does not depend on input")
+	}
+}
+
+func TestValidTag(t *testing.T) {
+	for tag, want := range map[string]bool{
+		"en": true, "fr": true, "fr-CA": true, "zh-Hant": true, "zh-Hant-TW": true,
+		"es-419": true, "en-XA": true,
+		"": false, "FR": false, "fr_CA": false, "english": false, "fr-ca": false,
+	} {
+		if got := ValidTag(tag); got != want {
+			t.Errorf("ValidTag(%q) = %v, want %v", tag, got, want)
+		}
+	}
+}
+
+func TestParseErrorsWrapped(t *testing.T) {
+	_, err := ParseEntries([]byte(`{"a":{"defaultMessage":"x","nope":1}}`))
+	if err == nil {
+		t.Fatal("expected error")
+	}
+	if errors.Unwrap(err) == nil {
+		t.Fatalf("error %v does not wrap a cause", err)
+	}
+}
+
+func mustParse(t *testing.T, s string) icu.Message {
+	t.Helper()
+	m, err := icu.Parse(s)
+	if err != nil {
+		t.Fatalf("icu.Parse(%q): %v", s, err)
+	}
+	return m
+}
diff --git a/i18n/pack/stamp.go b/i18n/pack/stamp.go
new file mode 100644
index 000000000..603f67d4f
--- /dev/null
+++ b/i18n/pack/stamp.go
@@ -0,0 +1,25 @@
+package pack
+
+// Stamp records the English source hash on every translated entry of tr that
+// lacks one, using ref for the English text. It returns the stamped entries
+// (tr itself is not modified) and whether anything changed.
+func Stamp(ref, tr map[string]Entry) (map[string]Entry, bool) {
+	out := make(map[string]Entry, len(tr))
+	for id, entry := range tr {
+		out[id] = entry
+	}
+	changed := false
+	for id, entry := range tr {
+		r, ok := ref[id]
+		if !ok || entry.SourceHash != "" {
+			continue
+		}
+		if EntryStatus(r, entry, true) != StatusTranslated {
+			continue
+		}
+		entry.SourceHash = SourceHash(r.DefaultMessage)
+		out[id] = entry
+		changed = true
+	}
+	return out, changed
+}
diff --git a/i18n/pack/stamp_test.go b/i18n/pack/stamp_test.go
new file mode 100644
index 000000000..c16952c6d
--- /dev/null
+++ b/i18n/pack/stamp_test.go
@@ -0,0 +1,37 @@
+package pack
+
+import "testing"
+
+func TestStampRecordsHashOnTranslatedEntries(t *testing.T) {
+	t.Parallel()
+	ref := map[string]Entry{
+		"a": {DefaultMessage: "Hello"},
+		"b": {DefaultMessage: "World"},
+		"c": {DefaultMessage: "Kept"},
+	}
+	tr := map[string]Entry{
+		"a": {DefaultMessage: "Bonjour"},
+		"b": {DefaultMessage: "{broken"}, // invalid ICU: not translated
+		"c": {DefaultMessage: "Garde", SourceHash: "abc"},
+		"x": {DefaultMessage: "Unknown id"},
+	}
+	out, changed := Stamp(ref, tr)
+	if !changed {
+		t.Fatal("expected a change")
+	}
+	if got := out["a"].SourceHash; got != SourceHash("Hello") {
+		t.Errorf("a hash = %q", got)
+	}
+	if out["b"].SourceHash != "" || out["x"].SourceHash != "" {
+		t.Errorf("invalid or unknown entries must not be stamped: %+v", out)
+	}
+	if out["c"].SourceHash != "abc" {
+		t.Errorf("existing hash replaced: %q", out["c"].SourceHash)
+	}
+	if tr["a"].SourceHash != "" {
+		t.Error("input map was modified")
+	}
+	if _, again := Stamp(ref, out); again {
+		t.Error("second stamp must be a no-op")
+	}
+}
diff --git a/i18n/pack/validate.go b/i18n/pack/validate.go
new file mode 100644
index 000000000..6ebcc75e5
--- /dev/null
+++ b/i18n/pack/validate.go
@@ -0,0 +1,240 @@
+package pack
+
+import (
+	"fmt"
+	"regexp"
+	"sort"
+	"strings"
+	"unicode/utf8"
+
+	"github.com/GameplanePanel/gameplane/i18n/icu"
+)
+
+// Severity classifies a Finding. Error findings fail the check; info findings
+// are advisory.
+type Severity string
+
+// Finding severities.
+const (
+	SeverityError Severity = "error"
+	SeverityInfo  Severity = "info"
+)
+
+// Finding codes reported by the validators.
+const (
+	CodeMalformedPack      = "malformed-pack"
+	CodeInvalidMeta        = "invalid-meta"
+	CodeICUSyntax          = "icu-syntax"
+	CodeMissingPlaceholder = "missing-placeholder"
+	CodeExtraPlaceholder   = "extra-placeholder"
+	CodeMarkup             = "markup"
+	CodeUnknownID          = "unknown-id"
+	CodeMissingDescription = "missing-description"
+	CodeExtractDrift       = "extract-drift"
+	CodeServerDrift        = "server-drift"
+	CodeUnusedID           = "unused-id"
+	CodeNeedsReview        = "needs-review"
+)
+
+// Pseudo-identifiers used in findings that are not about a message id.
+const (
+	IDPack      = "<pack>"
+	IDMeta      = "<meta>"
+	IDReference = "<reference>"
+	IDRegistry  = "<registry>"
+)
+
+// Finding is one problem reported by a validator.
+type Finding struct {
+	Code     string   `json:"code"`
+	Severity Severity `json:"severity"`
+	File     string   `json:"file"`
+	ID       string   `json:"id"`
+	Message  string   `json:"message"`
+}
+
+// String renders the finding as "<file>: <id>: [<code>] <message>".
+func (f Finding) String() string {
+	return fmt.Sprintf("%s: %s: [%s] %s", f.File, f.ID, f.Code, f.Message)
+}
+
+var (
+	entityRE = regexp.MustCompile(`&[A-Za-z#][A-Za-z0-9]*;`)
+)
+
+// CheckMarkup reports the first markup problem in a message, or "" when the
+// message only uses the allowed inline tags and no HTML entities or scripts.
+// raw is the message text as stored; m is its parsed form.
+func CheckMarkup(raw string, m icu.Message) string {
+	tags := icu.SortedKeys(icu.Tags(m))
+	for _, name := range tags {
+		if name != "b" && name != "link" {
+			return fmt.Sprintf("uses tag <%s>; only <b> and <link> are allowed", name)
+		}
+	}
+	if entityRE.MatchString(raw) {
+		return "contains an HTML entity"
+	}
+	lower := strings.ToLower(raw)
+	if strings.Contains(lower, "javascript:") {
+		return "contains a javascript: link"
+	}
+	if strings.Contains(lower, "<script") {
+		return "contains a script tag"
+	}
+	return ""
+}
+
+// ValidateReference checks every entry of the English reference: the message
+// must parse, use only allowed markup, and carry a translator description.
+func ValidateReference(ref map[string]Entry, file string) []Finding {
+	var out []Finding
+	for _, id := range sortedEntryIDs(ref) {
+		e := ref[id]
+		m, err := icu.Parse(e.DefaultMessage)
+		if err != nil {
+			out = append(out, errorFinding(CodeICUSyntax, file, id, fmt.Sprintf("does not parse: %v", err)))
+		} else if msg := CheckMarkup(e.DefaultMessage, m); msg != "" {
+			out = append(out, errorFinding(CodeMarkup, file, id, msg))
+		}
+		if strings.TrimSpace(e.Description) == "" {
+			out = append(out, errorFinding(CodeMissingDescription, file, id, "has no translator note (description)"))
+		}
+	}
+	return out
+}
+
+// ValidateMeta checks a meta.json file. dirTag is the directory name the file
+// lives in; the tag must match it.
+func ValidateMeta(data []byte, dirTag, file string) []Finding {
+	meta, err := ParseMeta(data)
+	if err != nil {
+		return []Finding{errorFinding(CodeInvalidMeta, file, IDMeta, fmt.Sprintf("meta.json is not valid: %v", err))}
+	}
+	var out []Finding
+	bad := func(msg string) {
+		out = append(out, errorFinding(CodeInvalidMeta, file, IDMeta, msg))
+	}
+	if meta.Tag == "" {
+		bad(`missing required field "tag"`)
+	} else {
+		if !ValidTag(meta.Tag) && meta.Tag != "en-XA" {
+			bad(fmt.Sprintf("tag %q is not a valid language tag", meta.Tag))
+		}
+		if dirTag != "" && meta.Tag != dirTag {
+			bad(fmt.Sprintf("tag %q does not match directory %q", meta.Tag, dirTag))
+		}
+	}
+	if meta.NativeName == "" {
+		bad(`missing required field "nativeName"`)
+	} else if utf8.RuneCountInString(meta.NativeName) > 64 {
+		bad("nativeName is longer than 64 characters")
+	}
+	if meta.EnglishName == "" {
+		bad(`missing required field "englishName"`)
+	} else if utf8.RuneCountInString(meta.EnglishName) > 64 {
+		bad("englishName is longer than 64 characters")
+	}
+	switch meta.Direction {
+	case "":
+		bad(`missing required field "direction"`)
+	case "ltr", "rtl":
+	default:
+		bad(fmt.Sprintf("direction %q must be \"ltr\" or \"rtl\"", meta.Direction))
+	}
+	return out
+}
+
+// ValidateTranslation checks a translated pack against the English reference.
+// Placeholder and markup problems are errors; a translation whose English
+// source has changed since it was made is reported as needs-review (info).
+func ValidateTranslation(ref, tr map[string]Entry, file string) []Finding {
+	var out []Finding
+	ids := sortedEntryIDs(tr)
+	for _, id := range ids {
+		e := tr[id]
+		refE, ok := ref[id]
+		if !ok {
+			out = append(out, errorFinding(CodeUnknownID, file, id, "translation for an id the English reference no longer has"))
+			continue
+		}
+		m, err := icu.Parse(e.DefaultMessage)
+		if err != nil {
+			out = append(out, errorFinding(CodeICUSyntax, file, id, fmt.Sprintf("does not parse: %v", err)))
+			continue
+		}
+		hasError := false
+		if refM, rerr := icu.Parse(refE.DefaultMessage); rerr == nil {
+			refArgs := icu.Arguments(refM)
+			trArgs := icu.Arguments(m)
+			if missing := setDifference(refArgs, trArgs); len(missing) > 0 {
+				out = append(out, errorFinding(CodeMissingPlaceholder, file, id, "missing placeholder(s): "+braceList(missing)))
+				hasError = true
+			}
+			if extra := setDifference(trArgs, refArgs); len(extra) > 0 {
+				out = append(out, errorFinding(CodeExtraPlaceholder, file, id, "placeholder(s) not in English: "+braceList(extra)))
+				hasError = true
+			}
+		}
+		if msg := CheckMarkup(e.DefaultMessage, m); msg != "" {
+			out = append(out, errorFinding(CodeMarkup, file, id, msg))
+			hasError = true
+		}
+		if !hasError && e.SourceHash != "" && e.SourceHash != SourceHash(refE.DefaultMessage) {
+			out = append(out, Finding{
+				Code:     CodeNeedsReview,
+				Severity: SeverityInfo,
+				File:     file,
+				ID:       id,
+				Message:  "English text changed since this was translated; please review",
+			})
+		}
+	}
+	return out
+}
+
+// SortFindings orders findings by file, then id, then code.
+func SortFindings(fs []Finding) {
+	sort.SliceStable(fs, func(i, j int) bool {
+		if fs[i].File != fs[j].File {
+			return fs[i].File < fs[j].File
+		}
+		if fs[i].ID != fs[j].ID {
+			return fs[i].ID < fs[j].ID
+		}
+		return fs[i].Code < fs[j].Code
+	})
+}
+
+func errorFinding(code, file, id, msg string) Finding {
+	return Finding{Code: code, Severity: SeverityError, File: file, ID: id, Message: msg}
+}
+
+func sortedEntryIDs(m map[string]Entry) []string {
+	ids := make([]string, 0, len(m))
+	for id := range m {
+		ids = append(ids, id)
+	}
+	sort.Strings(ids)
+	return ids
+}
+
+// setDifference returns the sorted members of a that are not in b.
+func setDifference(a, b map[string]struct{}) []string {
+	var out []string
+	for k := range a {
+		if _, ok := b[k]; !ok {
+			out = append(out, k)
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
+func braceList(names []string) string {
+	parts := make([]string, len(names))
+	for i, n := range names {
+		parts[i] = "{" + n + "}"
+	}
+	return strings.Join(parts, ", ")
+}
diff --git a/i18n/pack/validate_test.go b/i18n/pack/validate_test.go
new file mode 100644
index 000000000..465abfd50
--- /dev/null
+++ b/i18n/pack/validate_test.go
@@ -0,0 +1,186 @@
+package pack
+
+import (
+	"strings"
+	"testing"
+)
+
+func codes(fs []Finding) []string {
+	out := make([]string, 0, len(fs))
+	for _, f := range fs {
+		out = append(out, f.Code)
+	}
+	return out
+}
+
+func hasCode(fs []Finding, code string) bool {
+	for _, f := range fs {
+		if f.Code == code {
+			return true
+		}
+	}
+	return false
+}
+
+func TestFindingString(t *testing.T) {
+	f := Finding{Code: CodeUnusedID, Severity: SeverityError, File: "en/app.json", ID: "a.b", Message: "not used"}
+	want := "en/app.json: a.b: [unused-id] not used"
+	if got := f.String(); got != want {
+		t.Fatalf("String() = %q, want %q", got, want)
+	}
+}
+
+func TestCheckMarkup(t *testing.T) {
+	tests := []struct {
+		name string
+		raw  string
+		want string
+	}{
+		{name: "plain", raw: "Hello", want: ""},
+		{name: "allowed tags", raw: "<b>x</b> <link>y</link>", want: ""},
+		{name: "other tag", raw: "<i>x</i>", want: "uses tag <i>; only <b> and <link> are allowed"},
+		{name: "entity", raw: "a &amp; b", want: "contains an HTML entity"},
+		{name: "numeric entity", raw: "&#39;", want: "contains an HTML entity"},
+		{name: "javascript link", raw: "<link>JavaScript:alert(1)</link>", want: "contains a javascript: link"},
+		{name: "script tag", raw: "x '<script>'", want: "contains a script tag"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m := mustParse(t, tt.raw)
+			if got := CheckMarkup(tt.raw, m); got != tt.want {
+				t.Fatalf("CheckMarkup = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestValidateReferenceCodes(t *testing.T) {
+	ref := map[string]Entry{
+		"ok":         {DefaultMessage: "Hi <b>there</b>", Description: "greeting"},
+		"syntax":     {DefaultMessage: "Broken {", Description: "x"},
+		"markup":     {DefaultMessage: "<i>no</i>", Description: "x"},
+		"nodesc":     {DefaultMessage: "Plain"},
+		"whitespace": {DefaultMessage: "Plain", Description: "   "},
+	}
+	fs := ValidateReference(ref, "en/app.json")
+	for _, want := range []string{CodeICUSyntax, CodeMarkup, CodeMissingDescription} {
+		if !hasCode(fs, want) {
+			t.Errorf("missing code %s in %v", want, codes(fs))
+		}
+	}
+	for _, f := range fs {
+		if f.ID == "ok" {
+			t.Errorf("unexpected finding for ok: %v", f)
+		}
+		if f.Severity != SeverityError || f.File != "en/app.json" {
+			t.Errorf("bad finding shape: %+v", f)
+		}
+	}
+}
+
+func TestValidateMetaCodes(t *testing.T) {
+	good := `{"tag":"fr","nativeName":"Français","englishName":"French","direction":"ltr"}`
+	if fs := ValidateMeta([]byte(good), "fr", "fr/meta.json"); len(fs) != 0 {
+		t.Fatalf("valid meta produced findings: %v", fs)
+	}
+	tests := map[string]string{
+		"unknown key":   `{"tag":"fr","nativeName":"a","englishName":"b","direction":"ltr","x":1}`,
+		"missing tag":   `{"nativeName":"a","englishName":"b","direction":"ltr"}`,
+		"bad tag":       `{"tag":"f","nativeName":"a","englishName":"b","direction":"ltr"}`,
+		"dir mismatch":  `{"tag":"de","nativeName":"a","englishName":"b","direction":"ltr"}`,
+		"bad direction": `{"tag":"fr","nativeName":"a","englishName":"b","direction":"up"}`,
+		"long name":     `{"tag":"fr","nativeName":"` + strings.Repeat("x", 65) + `","englishName":"b","direction":"ltr"}`,
+		"no native":     `{"tag":"fr","englishName":"b","direction":"ltr"}`,
+	}
+	for name, in := range tests {
+		fs := ValidateMeta([]byte(in), "fr", "fr/meta.json")
+		if len(fs) == 0 {
+			t.Errorf("%s: expected findings", name)
+			continue
+		}
+		for _, f := range fs {
+			if f.Code != CodeInvalidMeta || f.ID != IDMeta {
+				t.Errorf("%s: bad finding %+v", name, f)
+			}
+		}
+	}
+}
+
+func TestValidateTranslationCodes(t *testing.T) {
+	ref := map[string]Entry{
+		"hello":   {DefaultMessage: "Hello {name}", Description: "greet"},
+		"files":   {DefaultMessage: "{n, plural, one {# file} other {# files}}", Description: "count"},
+		"link":    {DefaultMessage: "See <link>docs</link>", Description: "x"},
+		"changed": {DefaultMessage: "New text", Description: "x"},
+	}
+	tr := map[string]Entry{
+		"hello":   {DefaultMessage: "Bonjour"},
+		"files":   {DefaultMessage: "{n, plural, one {# fichier} other {# fichiers}}"},
+		"gone":    {DefaultMessage: "Old"},
+		"link":    {DefaultMessage: "Voir <i>docs</i>"},
+		"changed": {DefaultMessage: "Nouveau", SourceHash: "000000000000"},
+	}
+	// Translation with bad syntax.
+	tr["bad"] = Entry{DefaultMessage: "{x"}
+	ref["bad"] = Entry{DefaultMessage: "x", Description: "x"}
+	// Extra placeholder.
+	ref["extra"] = Entry{DefaultMessage: "Plain", Description: "x"}
+	tr["extra"] = Entry{DefaultMessage: "Plain {who}"}
+
+	fs := ValidateTranslation(ref, tr, "fr/app.json")
+	want := map[string]string{
+		"hello":   CodeMissingPlaceholder,
+		"extra":   CodeExtraPlaceholder,
+		"gone":    CodeUnknownID,
+		"bad":     CodeICUSyntax,
+		"link":    CodeMarkup,
+		"changed": CodeNeedsReview,
+	}
+	for id, code := range want {
+		found := false
+		for _, f := range fs {
+			if f.ID == id && f.Code == code {
+				found = true
+			}
+		}
+		if !found {
+			t.Errorf("%s: missing %s in %v", id, code, fs)
+		}
+	}
+	for _, f := range fs {
+		if f.ID == "files" {
+			t.Errorf("unexpected finding for files: %v", f)
+		}
+		if f.Code == CodeNeedsReview && f.Severity != SeverityInfo {
+			t.Errorf("needs-review must be info, got %s", f.Severity)
+		}
+	}
+}
+
+func TestValidateTranslationNeedsReviewOnlyWhenNoErrors(t *testing.T) {
+	ref := map[string]Entry{"a": {DefaultMessage: "A {x}", Description: "d"}}
+	tr := map[string]Entry{"a": {DefaultMessage: "B", SourceHash: "000000000000"}}
+	fs := ValidateTranslation(ref, tr, "fr/app.json")
+	if hasCode(fs, CodeNeedsReview) {
+		t.Fatalf("needs-review reported alongside an error: %v", fs)
+	}
+	if !hasCode(fs, CodeMissingPlaceholder) {
+		t.Fatalf("expected missing-placeholder: %v", fs)
+	}
+}
+
+func TestSortFindings(t *testing.T) {
+	fs := []Finding{
+		{File: "b", ID: "x", Code: "a"},
+		{File: "a", ID: "z", Code: "a"},
+		{File: "a", ID: "y", Code: "b"},
+		{File: "a", ID: "y", Code: "a"},
+	}
+	SortFindings(fs)
+	want := []string{"a/y/a", "a/y/b", "a/z/a", "b/x/a"}
+	for i, f := range fs {
+		if got := f.File + "/" + f.ID + "/" + f.Code; got != want[i] {
+			t.Fatalf("pos %d = %s, want %s", i, got, want[i])
+		}
+	}
+}
diff --git a/i18n/specs.md b/i18n/specs.md
new file mode 100644
index 000000000..fd21aa03e
--- /dev/null
+++ b/i18n/specs.md
@@ -0,0 +1,67 @@
+# i18n — Specification
+
+**Status:** pre-v1 (spec 019)
+**Module / package:** `github.com/GameplanePanel/gameplane/i18n`
+**Dependencies:** stdlib, `golang.org/x/text` and `gopkg.in/yaml.v3` (the `i18n-check --module` mode reads module manifests; Go 1.26+)
+
+## Purpose
+
+Shared language packs for the dashboard, the API, the operator and the module tooling. One module owns the English reference catalog, the translated packs, the ICU message formatter, the pack validator and the `i18n-check` CI command, so every consumer reads the same messages and the same rules decide which translations ship.
+
+The feature's design is in [`../specs/019-localization-language-packs/spec.md`](../specs/019-localization-language-packs/spec.md).
+
+## Responsibilities
+
+1. Hold the English reference catalog `locales/en/app.json` and the translated packs `locales/<tag>/app.json` with their `meta.json`, embedded at build time.
+2. Parse and format the ICU MessageFormat subset (`icu`): arguments, number, date and time, plural, select, tags and apostrophe quoting.
+3. Parse, marshal and hash pack files, and define the pack metadata (`pack`).
+4. Validate the reference, metadata and translations, and compute completeness and listing status (`pack`).
+5. Load the embedded packs and look messages up with a regional, base-language and reference fallback (`catalog`).
+6. Run the CI checks, sync the server-side registry, stamp source hashes and write the language manifest and the summary (`cmd/i18n-check`).
+
+## Non-goals / boundaries
+
+- Does **not** translate text. Translations are produced and reviewed outside the code.
+- Does **not** render a page, a notification or a console line. Consumers call `catalog.Lookup` and decide where the text goes.
+- Does **not** talk to the network. The server registry arrives as a file passed to `i18n-check`.
+- Does **not** store per-user language choices. The API and the dashboard own those.
+- Does **not** accept HTML. Translations may use only the `<b>` and `<link>` tags, and no HTML entities or script links.
+
+## Directory & package layout
+
+```
+i18n/
+├── doc.go              # package comment
+├── embed.go            # go:embed locales/*/*.json → Locales (root package: embed paths cannot use "..")
+├── locales/
+│   ├── en/app.json     # reference catalog; GENERATED by i18n-check tooling, never hand-edited
+│   ├── en/meta.json    # reference metadata (tag, nativeName, englishName, direction)
+│   └── <tag>/…         # translated packs
+├── icu/                # parse.go, placeholders.go, format.go: ICU subset
+├── pack/               # pack.go (types, parse, marshal, hash, tags), validate.go, completeness.go, stamp.go
+├── modlocale/          # ids.go: module id derivation (Derive, ValidID) shared by gp-module, i18n-check --module and the operator
+├── catalog/            # catalog.go: Load, Default, lookup chain, listing
+├── cmd/i18n-check/     # main.go: CLI, app mode and module mode (--module: en.json must equal the ids derived from template.yaml + module.yaml; --stamp is app-mode only)
+├── testdata/defective/ # one fixture per finding code (SC-007)
+├── .testcoverage.yml   # 90% coverage gate
+└── go.mod
+```
+
+## Consumers
+
+- **web** — build-time import of `locales/` (through the pack files) so the dashboard ships only the messages it uses.
+- **api** — notification text and language validation (`catalog.IsListed`, `catalog.Tags`).
+- **operator** — module locales and the language a module reports.
+- **gp-module** — validates module locales with the same pack rules.
+- **module-repo CI** — runs `i18n-check` in module mode against each module's flat `en.json` and `<tag>.json` files.
+
+## Invariants
+
+1. The reference `locales/en/app.json` is generated and never hand-edited. Changes come from the extraction or server-sync step of `i18n-check`.
+2. `ListingThreshold` is 80: a language is listed only at 80% completeness or more, is left-to-right, and is not the `en-XA` pseudo-locale. The reference is always listed.
+3. Invalid translations are never shown. A translation that fails to parse, changes placeholders or uses disallowed markup is dropped before `catalog` sees it, and lookup falls back to the next pack or to English.
+4. A translation whose English source changed since it was translated is still shown, but reported as `needs-review`.
+
+## Pack format and check tool
+
+The pack format and the `i18n-check` behaviour are defined by the binding contracts [`pack-format.md`](../specs/019-localization-language-packs/contracts/pack-format.md) and [`check-tool.md`](../specs/019-localization-language-packs/contracts/check-tool.md). One addition to `check-tool.md`: `--sync-server` and `--check-server` read the API message registry from `--registry <file>` (the JSON array written by `api/cmd/messages-export`).
diff --git a/i18n/testdata/defective/extra-placeholder/en/app.json b/i18n/testdata/defective/extra-placeholder/en/app.json
new file mode 100644
index 000000000..5d688cbe7
--- /dev/null
+++ b/i18n/testdata/defective/extra-placeholder/en/app.json
@@ -0,0 +1,14 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {
+    "defaultMessage": "Hello",
+    "description": "Greeting on the home page"
+  },
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/extra-placeholder/xx/app.json b/i18n/testdata/defective/extra-placeholder/xx/app.json
new file mode 100644
index 000000000..59c6ee891
--- /dev/null
+++ b/i18n/testdata/defective/extra-placeholder/xx/app.json
@@ -0,0 +1,5 @@
+{
+  "files.count": {"defaultMessage": "{n, plural, one {# fichier} other {# fichiers}}"},
+  "greeting": {"defaultMessage": "Bonjour {name}"},
+  "welcome": {"defaultMessage": "Bienvenue sur <b>Gameplane</b>"}
+}
diff --git a/i18n/testdata/defective/extra-placeholder/xx/meta.json b/i18n/testdata/defective/extra-placeholder/xx/meta.json
new file mode 100644
index 000000000..f4c1eb2c1
--- /dev/null
+++ b/i18n/testdata/defective/extra-placeholder/xx/meta.json
@@ -0,0 +1 @@
+{"tag": "xx", "nativeName": "Test", "englishName": "Test", "direction": "ltr"}
diff --git a/i18n/testdata/defective/extract-drift/args b/i18n/testdata/defective/extract-drift/args
new file mode 100644
index 000000000..0f4a58806
--- /dev/null
+++ b/i18n/testdata/defective/extract-drift/args
@@ -0,0 +1 @@
+--extracted {dir}/extracted.json
diff --git a/i18n/testdata/defective/extract-drift/en/app.json b/i18n/testdata/defective/extract-drift/en/app.json
new file mode 100644
index 000000000..5d688cbe7
--- /dev/null
+++ b/i18n/testdata/defective/extract-drift/en/app.json
@@ -0,0 +1,14 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {
+    "defaultMessage": "Hello",
+    "description": "Greeting on the home page"
+  },
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/extract-drift/extracted.json b/i18n/testdata/defective/extract-drift/extracted.json
new file mode 100644
index 000000000..730d93ab3
--- /dev/null
+++ b/i18n/testdata/defective/extract-drift/extracted.json
@@ -0,0 +1,14 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {
+    "defaultMessage": "Hi",
+    "description": "Greeting on the home page"
+  },
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/extract-drift/xx/app.json b/i18n/testdata/defective/extract-drift/xx/app.json
new file mode 100644
index 000000000..f91f3064b
--- /dev/null
+++ b/i18n/testdata/defective/extract-drift/xx/app.json
@@ -0,0 +1,11 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# fichier} other {# fichiers}}"
+  },
+  "greeting": {
+    "defaultMessage": "Bonjour"
+  },
+  "welcome": {
+    "defaultMessage": "Bienvenue sur <b>Gameplane</b>"
+  }
+}
diff --git a/i18n/testdata/defective/extract-drift/xx/meta.json b/i18n/testdata/defective/extract-drift/xx/meta.json
new file mode 100644
index 000000000..f4c1eb2c1
--- /dev/null
+++ b/i18n/testdata/defective/extract-drift/xx/meta.json
@@ -0,0 +1 @@
+{"tag": "xx", "nativeName": "Test", "englishName": "Test", "direction": "ltr"}
diff --git a/i18n/testdata/defective/icu-syntax/en/app.json b/i18n/testdata/defective/icu-syntax/en/app.json
new file mode 100644
index 000000000..5d688cbe7
--- /dev/null
+++ b/i18n/testdata/defective/icu-syntax/en/app.json
@@ -0,0 +1,14 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {
+    "defaultMessage": "Hello",
+    "description": "Greeting on the home page"
+  },
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/icu-syntax/xx/app.json b/i18n/testdata/defective/icu-syntax/xx/app.json
new file mode 100644
index 000000000..d4a4055a7
--- /dev/null
+++ b/i18n/testdata/defective/icu-syntax/xx/app.json
@@ -0,0 +1,5 @@
+{
+  "files.count": {"defaultMessage": "{n, plural, one {# fichier} other {# fichiers}}"},
+  "greeting": {"defaultMessage": "Bonjour {name"},
+  "welcome": {"defaultMessage": "Bienvenue sur <b>Gameplane</b>"}
+}
diff --git a/i18n/testdata/defective/icu-syntax/xx/meta.json b/i18n/testdata/defective/icu-syntax/xx/meta.json
new file mode 100644
index 000000000..f4c1eb2c1
--- /dev/null
+++ b/i18n/testdata/defective/icu-syntax/xx/meta.json
@@ -0,0 +1 @@
+{"tag": "xx", "nativeName": "Test", "englishName": "Test", "direction": "ltr"}
diff --git a/i18n/testdata/defective/invalid-meta/en/app.json b/i18n/testdata/defective/invalid-meta/en/app.json
new file mode 100644
index 000000000..5d688cbe7
--- /dev/null
+++ b/i18n/testdata/defective/invalid-meta/en/app.json
@@ -0,0 +1,14 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {
+    "defaultMessage": "Hello",
+    "description": "Greeting on the home page"
+  },
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/invalid-meta/xx/app.json b/i18n/testdata/defective/invalid-meta/xx/app.json
new file mode 100644
index 000000000..f91f3064b
--- /dev/null
+++ b/i18n/testdata/defective/invalid-meta/xx/app.json
@@ -0,0 +1,11 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# fichier} other {# fichiers}}"
+  },
+  "greeting": {
+    "defaultMessage": "Bonjour"
+  },
+  "welcome": {
+    "defaultMessage": "Bienvenue sur <b>Gameplane</b>"
+  }
+}
diff --git a/i18n/testdata/defective/invalid-meta/xx/meta.json b/i18n/testdata/defective/invalid-meta/xx/meta.json
new file mode 100644
index 000000000..051325108
--- /dev/null
+++ b/i18n/testdata/defective/invalid-meta/xx/meta.json
@@ -0,0 +1 @@
+{"tag": "xx", "nativeName": "Test", "englishName": "Test"}
diff --git a/i18n/testdata/defective/malformed-pack/en/app.json b/i18n/testdata/defective/malformed-pack/en/app.json
new file mode 100644
index 000000000..5d688cbe7
--- /dev/null
+++ b/i18n/testdata/defective/malformed-pack/en/app.json
@@ -0,0 +1,14 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {
+    "defaultMessage": "Hello",
+    "description": "Greeting on the home page"
+  },
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/malformed-pack/xx/app.json b/i18n/testdata/defective/malformed-pack/xx/app.json
new file mode 100644
index 000000000..5e63c340e
--- /dev/null
+++ b/i18n/testdata/defective/malformed-pack/xx/app.json
@@ -0,0 +1 @@
+{"greeting": {"defaultMessage": "Bonjour"
diff --git a/i18n/testdata/defective/malformed-pack/xx/meta.json b/i18n/testdata/defective/malformed-pack/xx/meta.json
new file mode 100644
index 000000000..f4c1eb2c1
--- /dev/null
+++ b/i18n/testdata/defective/malformed-pack/xx/meta.json
@@ -0,0 +1 @@
+{"tag": "xx", "nativeName": "Test", "englishName": "Test", "direction": "ltr"}
diff --git a/i18n/testdata/defective/markup/en/app.json b/i18n/testdata/defective/markup/en/app.json
new file mode 100644
index 000000000..5d688cbe7
--- /dev/null
+++ b/i18n/testdata/defective/markup/en/app.json
@@ -0,0 +1,14 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {
+    "defaultMessage": "Hello",
+    "description": "Greeting on the home page"
+  },
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/markup/xx/app.json b/i18n/testdata/defective/markup/xx/app.json
new file mode 100644
index 000000000..7ce6f0225
--- /dev/null
+++ b/i18n/testdata/defective/markup/xx/app.json
@@ -0,0 +1,5 @@
+{
+  "files.count": {"defaultMessage": "{n, plural, one {# fichier} other {# fichiers}}"},
+  "greeting": {"defaultMessage": "Bonjour"},
+  "welcome": {"defaultMessage": "Bienvenue sur <i>Gameplane</i>"}
+}
diff --git a/i18n/testdata/defective/markup/xx/meta.json b/i18n/testdata/defective/markup/xx/meta.json
new file mode 100644
index 000000000..f4c1eb2c1
--- /dev/null
+++ b/i18n/testdata/defective/markup/xx/meta.json
@@ -0,0 +1 @@
+{"tag": "xx", "nativeName": "Test", "englishName": "Test", "direction": "ltr"}
diff --git a/i18n/testdata/defective/missing-description/en/app.json b/i18n/testdata/defective/missing-description/en/app.json
new file mode 100644
index 000000000..881d7bf15
--- /dev/null
+++ b/i18n/testdata/defective/missing-description/en/app.json
@@ -0,0 +1,11 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {"defaultMessage": "Hello"},
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/missing-description/xx/app.json b/i18n/testdata/defective/missing-description/xx/app.json
new file mode 100644
index 000000000..f91f3064b
--- /dev/null
+++ b/i18n/testdata/defective/missing-description/xx/app.json
@@ -0,0 +1,11 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# fichier} other {# fichiers}}"
+  },
+  "greeting": {
+    "defaultMessage": "Bonjour"
+  },
+  "welcome": {
+    "defaultMessage": "Bienvenue sur <b>Gameplane</b>"
+  }
+}
diff --git a/i18n/testdata/defective/missing-description/xx/meta.json b/i18n/testdata/defective/missing-description/xx/meta.json
new file mode 100644
index 000000000..f4c1eb2c1
--- /dev/null
+++ b/i18n/testdata/defective/missing-description/xx/meta.json
@@ -0,0 +1 @@
+{"tag": "xx", "nativeName": "Test", "englishName": "Test", "direction": "ltr"}
diff --git a/i18n/testdata/defective/missing-placeholder/en/app.json b/i18n/testdata/defective/missing-placeholder/en/app.json
new file mode 100644
index 000000000..5d688cbe7
--- /dev/null
+++ b/i18n/testdata/defective/missing-placeholder/en/app.json
@@ -0,0 +1,14 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {
+    "defaultMessage": "Hello",
+    "description": "Greeting on the home page"
+  },
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/missing-placeholder/xx/app.json b/i18n/testdata/defective/missing-placeholder/xx/app.json
new file mode 100644
index 000000000..0cbde8999
--- /dev/null
+++ b/i18n/testdata/defective/missing-placeholder/xx/app.json
@@ -0,0 +1,5 @@
+{
+  "files.count": {"defaultMessage": "Plusieurs fichiers"},
+  "greeting": {"defaultMessage": "Bonjour"},
+  "welcome": {"defaultMessage": "Bienvenue sur <b>Gameplane</b>"}
+}
diff --git a/i18n/testdata/defective/missing-placeholder/xx/meta.json b/i18n/testdata/defective/missing-placeholder/xx/meta.json
new file mode 100644
index 000000000..f4c1eb2c1
--- /dev/null
+++ b/i18n/testdata/defective/missing-placeholder/xx/meta.json
@@ -0,0 +1 @@
+{"tag": "xx", "nativeName": "Test", "englishName": "Test", "direction": "ltr"}
diff --git a/i18n/testdata/defective/needs-review/en/app.json b/i18n/testdata/defective/needs-review/en/app.json
new file mode 100644
index 000000000..5d688cbe7
--- /dev/null
+++ b/i18n/testdata/defective/needs-review/en/app.json
@@ -0,0 +1,14 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {
+    "defaultMessage": "Hello",
+    "description": "Greeting on the home page"
+  },
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/needs-review/xx/app.json b/i18n/testdata/defective/needs-review/xx/app.json
new file mode 100644
index 000000000..e2d2dde9d
--- /dev/null
+++ b/i18n/testdata/defective/needs-review/xx/app.json
@@ -0,0 +1,5 @@
+{
+  "files.count": {"defaultMessage": "{n, plural, one {# fichier} other {# fichiers}}"},
+  "greeting": {"defaultMessage": "Bonjour", "sourceHash": "000000000000"},
+  "welcome": {"defaultMessage": "Bienvenue sur <b>Gameplane</b>"}
+}
diff --git a/i18n/testdata/defective/needs-review/xx/meta.json b/i18n/testdata/defective/needs-review/xx/meta.json
new file mode 100644
index 000000000..f4c1eb2c1
--- /dev/null
+++ b/i18n/testdata/defective/needs-review/xx/meta.json
@@ -0,0 +1 @@
+{"tag": "xx", "nativeName": "Test", "englishName": "Test", "direction": "ltr"}
diff --git a/i18n/testdata/defective/server-drift/args b/i18n/testdata/defective/server-drift/args
new file mode 100644
index 000000000..89262ac69
--- /dev/null
+++ b/i18n/testdata/defective/server-drift/args
@@ -0,0 +1 @@
+--registry {dir}/registry.json --check-server
diff --git a/i18n/testdata/defective/server-drift/en/app.json b/i18n/testdata/defective/server-drift/en/app.json
new file mode 100644
index 000000000..8202689d2
--- /dev/null
+++ b/i18n/testdata/defective/server-drift/en/app.json
@@ -0,0 +1,18 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {
+    "defaultMessage": "Hello",
+    "description": "Greeting on the home page"
+  },
+  "server.motd": {
+    "defaultMessage": "Message of the day",
+    "description": "Shown on the server page"
+  },
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/server-drift/registry.json b/i18n/testdata/defective/server-drift/registry.json
new file mode 100644
index 000000000..684a1c27b
--- /dev/null
+++ b/i18n/testdata/defective/server-drift/registry.json
@@ -0,0 +1 @@
+[{"id": "server.motd", "english": "Daily message", "description": "Shown on the server page"}]
diff --git a/i18n/testdata/defective/server-drift/xx/app.json b/i18n/testdata/defective/server-drift/xx/app.json
new file mode 100644
index 000000000..f91f3064b
--- /dev/null
+++ b/i18n/testdata/defective/server-drift/xx/app.json
@@ -0,0 +1,11 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# fichier} other {# fichiers}}"
+  },
+  "greeting": {
+    "defaultMessage": "Bonjour"
+  },
+  "welcome": {
+    "defaultMessage": "Bienvenue sur <b>Gameplane</b>"
+  }
+}
diff --git a/i18n/testdata/defective/server-drift/xx/meta.json b/i18n/testdata/defective/server-drift/xx/meta.json
new file mode 100644
index 000000000..f4c1eb2c1
--- /dev/null
+++ b/i18n/testdata/defective/server-drift/xx/meta.json
@@ -0,0 +1 @@
+{"tag": "xx", "nativeName": "Test", "englishName": "Test", "direction": "ltr"}
diff --git a/i18n/testdata/defective/unknown-id/en/app.json b/i18n/testdata/defective/unknown-id/en/app.json
new file mode 100644
index 000000000..5d688cbe7
--- /dev/null
+++ b/i18n/testdata/defective/unknown-id/en/app.json
@@ -0,0 +1,14 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {
+    "defaultMessage": "Hello",
+    "description": "Greeting on the home page"
+  },
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/unknown-id/xx/app.json b/i18n/testdata/defective/unknown-id/xx/app.json
new file mode 100644
index 000000000..adb021986
--- /dev/null
+++ b/i18n/testdata/defective/unknown-id/xx/app.json
@@ -0,0 +1,6 @@
+{
+  "files.count": {"defaultMessage": "{n, plural, one {# fichier} other {# fichiers}}"},
+  "farewell": {"defaultMessage": "Au revoir"},
+  "greeting": {"defaultMessage": "Bonjour"},
+  "welcome": {"defaultMessage": "Bienvenue sur <b>Gameplane</b>"}
+}
diff --git a/i18n/testdata/defective/unknown-id/xx/meta.json b/i18n/testdata/defective/unknown-id/xx/meta.json
new file mode 100644
index 000000000..f4c1eb2c1
--- /dev/null
+++ b/i18n/testdata/defective/unknown-id/xx/meta.json
@@ -0,0 +1 @@
+{"tag": "xx", "nativeName": "Test", "englishName": "Test", "direction": "ltr"}
diff --git a/i18n/testdata/defective/unused-id/args b/i18n/testdata/defective/unused-id/args
new file mode 100644
index 000000000..5e68f282a
--- /dev/null
+++ b/i18n/testdata/defective/unused-id/args
@@ -0,0 +1 @@
+--used-ids {dir}/used-ids.txt
diff --git a/i18n/testdata/defective/unused-id/en/app.json b/i18n/testdata/defective/unused-id/en/app.json
new file mode 100644
index 000000000..5d688cbe7
--- /dev/null
+++ b/i18n/testdata/defective/unused-id/en/app.json
@@ -0,0 +1,14 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# file} other {# files}}",
+    "description": "Number of files in a folder"
+  },
+  "greeting": {
+    "defaultMessage": "Hello",
+    "description": "Greeting on the home page"
+  },
+  "welcome": {
+    "defaultMessage": "Welcome to <b>Gameplane</b>",
+    "description": "Welcome line under the logo"
+  }
+}
diff --git a/i18n/testdata/defective/unused-id/used-ids.txt b/i18n/testdata/defective/unused-id/used-ids.txt
new file mode 100644
index 000000000..c7c8841e4
--- /dev/null
+++ b/i18n/testdata/defective/unused-id/used-ids.txt
@@ -0,0 +1,2 @@
+greeting
+welcome
diff --git a/i18n/testdata/defective/unused-id/xx/app.json b/i18n/testdata/defective/unused-id/xx/app.json
new file mode 100644
index 000000000..f91f3064b
--- /dev/null
+++ b/i18n/testdata/defective/unused-id/xx/app.json
@@ -0,0 +1,11 @@
+{
+  "files.count": {
+    "defaultMessage": "{n, plural, one {# fichier} other {# fichiers}}"
+  },
+  "greeting": {
+    "defaultMessage": "Bonjour"
+  },
+  "welcome": {
+    "defaultMessage": "Bienvenue sur <b>Gameplane</b>"
+  }
+}
diff --git a/i18n/testdata/defective/unused-id/xx/meta.json b/i18n/testdata/defective/unused-id/xx/meta.json
new file mode 100644
index 000000000..f4c1eb2c1
--- /dev/null
+++ b/i18n/testdata/defective/unused-id/xx/meta.json
@@ -0,0 +1 @@
+{"tag": "xx", "nativeName": "Test", "englishName": "Test", "direction": "ltr"}
diff --git a/operator/Dockerfile b/operator/Dockerfile
index 00c7f66b9..46e6b9a90 100644
--- a/operator/Dockerfile
+++ b/operator/Dockerfile
@@ -3,7 +3,9 @@ WORKDIR /src
 
 # netguard is an in-repo module the operator depends on via a local replace
 # (../netguard); copy it first so `go mod download` and the build resolve it.
+# i18n (module locales, spec 019) is copied ahead of the operator importing it.
 COPY netguard/ ./netguard/
+COPY i18n/ ./i18n/
 COPY operator/go.mod operator/go.sum* ./operator/
 WORKDIR /src/operator
 RUN go mod download
diff --git a/operator/api/v1alpha1/gameserver_types.go b/operator/api/v1alpha1/gameserver_types.go
index 447d0ce4d..654cba6ed 100644
--- a/operator/api/v1alpha1/gameserver_types.go
+++ b/operator/api/v1alpha1/gameserver_types.go
@@ -523,6 +523,16 @@ type GameServerStatus struct {
 	// +patchStrategy=merge
 	Conditions []metav1.Condition `json:"conditions,omitempty" patchStrategy:"merge" patchMergeKey:"type"`
 
+	// ConditionArgs carries, per condition Type, the values interpolated into
+	// that condition's English message, so clients can render the localized
+	// message for the condition's current Reason (translation id
+	// condition.<type>.<reason>, lower-cased). The English Message is
+	// unchanged and stays the fallback. An entry exists only while the
+	// condition's current Reason has arguments; it is removed when the Reason
+	// changes to one without.
+	// +optional
+	ConditionArgs map[string]map[string]string `json:"conditionArgs,omitempty"`
+
 	// Endpoints lists the externally reachable addresses advertised for
 	// this server (populated once the Service is reconciled).
 	// +optional
diff --git a/operator/api/v1alpha1/gametemplate_types.go b/operator/api/v1alpha1/gametemplate_types.go
index 481162654..bea234aea 100644
--- a/operator/api/v1alpha1/gametemplate_types.go
+++ b/operator/api/v1alpha1/gametemplate_types.go
@@ -1213,8 +1213,19 @@ type GameTemplateStatus struct {
 	// this template.
 	// +optional
 	InUseCount int32 `json:"inUseCount,omitempty"`
+
+	// Conditions carry detailed state. LocalesValid reports whether the
+	// translations shipped with the module bundle were all valid.
+	// +optional
+	// +patchMergeKey=type
+	// +patchStrategy=merge
+	Conditions []metav1.Condition `json:"conditions,omitempty" patchStrategy:"merge" patchMergeKey:"type"`
 }
 
+// GameTemplateConditionLocalesValid is the GameTemplate condition that reports
+// the validity of the module's translations.
+const GameTemplateConditionLocalesValid = "LocalesValid"
+
 // +kubebuilder:object:root=true
 // +kubebuilder:resource:scope=Cluster,shortName=gtmpl;gametmpl
 // +kubebuilder:printcolumn:name="Game",type=string,JSONPath=`.spec.game`
diff --git a/operator/api/v1alpha1/zz_generated.deepcopy.go b/operator/api/v1alpha1/zz_generated.deepcopy.go
index 891ebdd56..05926fd58 100644
--- a/operator/api/v1alpha1/zz_generated.deepcopy.go
+++ b/operator/api/v1alpha1/zz_generated.deepcopy.go
@@ -1049,6 +1049,24 @@ func (in *GameServerStatus) DeepCopyInto(out *GameServerStatus) {
 			(*in)[i].DeepCopyInto(&(*out)[i])
 		}
 	}
+	if in.ConditionArgs != nil {
+		in, out := &in.ConditionArgs, &out.ConditionArgs
+		*out = make(map[string]map[string]string, len(*in))
+		for key, val := range *in {
+			var outVal map[string]string
+			if val == nil {
+				(*out)[key] = nil
+			} else {
+				inVal := (*in)[key]
+				in, out := &inVal, &outVal
+				*out = make(map[string]string, len(*in))
+				for key, val := range *in {
+					(*out)[key] = val
+				}
+			}
+			(*out)[key] = outVal
+		}
+	}
 	if in.Endpoints != nil {
 		in, out := &in.Endpoints, &out.Endpoints
 		*out = make([]GameServerEndpoint, len(*in))
@@ -1168,7 +1186,7 @@ func (in *GameTemplate) DeepCopyInto(out *GameTemplate) {
 	out.TypeMeta = in.TypeMeta
 	in.ObjectMeta.DeepCopyInto(&out.ObjectMeta)
 	in.Spec.DeepCopyInto(&out.Spec)
-	out.Status = in.Status
+	in.Status.DeepCopyInto(&out.Status)
 }
 
 // DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new GameTemplate.
@@ -1327,6 +1345,13 @@ func (in *GameTemplateSpec) DeepCopy() *GameTemplateSpec {
 // DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
 func (in *GameTemplateStatus) DeepCopyInto(out *GameTemplateStatus) {
 	*out = *in
+	if in.Conditions != nil {
+		in, out := &in.Conditions, &out.Conditions
+		*out = make([]v1.Condition, len(*in))
+		for i := range *in {
+			(*in)[i].DeepCopyInto(&(*out)[i])
+		}
+	}
 }
 
 // DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new GameTemplateStatus.
diff --git a/operator/cmd/main.go b/operator/cmd/main.go
index 4d2432087..85263e901 100644
--- a/operator/cmd/main.go
+++ b/operator/cmd/main.go
@@ -209,7 +209,7 @@ func main() {
 		"Log level (debug, info, warn, or error) injected into agent sidecars as GAMEPLANE_LOG_LEVEL. "+
 			"Empty injects nothing (the agent defaults to info) and avoids rolling existing pods.")
 	flag.StringVar(&moduleNamespace, "module-namespace", "gameplane-system",
-		"Namespace where ModuleSource credential Secrets live.")
+		"Namespace where ModuleSource credential Secrets, uploaded module bundles and module translation ConfigMaps live.")
 	flag.StringVar(&moduleLocalRoot, "module-local-root", "",
 		"Base directory that local-type ModuleSources resolve their paths under. Empty disables local sources.")
 	flag.StringVar(&agentCABundle, "agent-ca-bundle", "",
@@ -478,6 +478,7 @@ func main() {
 		Namespace:       moduleNamespace,
 		OperatorVersion: Version,
 		FetchOptions:    fetchOptions,
+		EventRecorder:   mgr.GetEventRecorder("module-controller"),
 	}).SetupWithManager(mgr); err != nil {
 		setupLog.Error(err, "unable to set up controller", "controller", "Module")
 		os.Exit(1)
diff --git a/operator/config/crd/gameplane.local_gameservers.yaml b/operator/config/crd/gameplane.local_gameservers.yaml
index ea998dc82..4be670ebc 100644
--- a/operator/config/crd/gameplane.local_gameservers.yaml
+++ b/operator/config/crd/gameplane.local_gameservers.yaml
@@ -2441,6 +2441,20 @@ spec:
                     format: int32
                     type: integer
                 type: object
+              conditionArgs:
+                additionalProperties:
+                  additionalProperties:
+                    type: string
+                  type: object
+                description: |-
+                  ConditionArgs carries, per condition Type, the values interpolated into
+                  that condition's English message, so clients can render the localized
+                  message for the condition's current Reason (translation id
+                  condition.<type>.<reason>, lower-cased). The English Message is
+                  unchanged and stays the fallback. An entry exists only while the
+                  condition's current Reason has arguments; it is removed when the Reason
+                  changes to one without.
+                type: object
               conditions:
                 description: |-
                   Conditions carry detailed state transitions. Standard Ready,
diff --git a/operator/config/crd/gameplane.local_gametemplates.yaml b/operator/config/crd/gameplane.local_gametemplates.yaml
index b1f163b37..13d8a1fa5 100644
--- a/operator/config/crd/gameplane.local_gametemplates.yaml
+++ b/operator/config/crd/gameplane.local_gametemplates.yaml
@@ -2476,6 +2476,65 @@ spec:
               static configuration. The operator populates ObservedGeneration so
               controllers reading templates can detect spec updates.
             properties:
+              conditions:
+                description: |-
+                  Conditions carry detailed state. LocalesValid reports whether the
+                  translations shipped with the module bundle were all valid.
+                items:
+                  description: Condition contains details for one aspect of the current
+                    state of this API Resource.
+                  properties:
+                    lastTransitionTime:
+                      description: |-
+                        lastTransitionTime is the last time the condition transitioned from one status to another.
+                        This should be when the underlying condition changed.  If that is not known, then using the time when the API field changed is acceptable.
+                      format: date-time
+                      type: string
+                    message:
+                      description: |-
+                        message is a human readable message indicating details about the transition.
+                        This may be an empty string.
+                      maxLength: 32768
+                      type: string
+                    observedGeneration:
+                      description: |-
+                        observedGeneration represents the .metadata.generation that the condition was set based upon.
+                        For instance, if .metadata.generation is currently 12, but the .status.conditions[x].observedGeneration is 9, the condition is out of date
+                        with respect to the current state of the instance.
+                      format: int64
+                      minimum: 0
+                      type: integer
+                    reason:
+                      description: |-
+                        reason contains a programmatic identifier indicating the reason for the condition's last transition.
+                        Producers of specific condition types may define expected values and meanings for this field,
+                        and whether the values are considered a guaranteed API.
+                        The value should be a CamelCase string.
+                        This field may not be empty.
+                      maxLength: 1024
+                      minLength: 1
+                      pattern: ^[A-Za-z]([A-Za-z0-9_,:]*[A-Za-z0-9_])?$
+                      type: string
+                    status:
+                      description: status of the condition, one of True, False, Unknown.
+                      enum:
+                      - "True"
+                      - "False"
+                      - Unknown
+                      type: string
+                    type:
+                      description: type of condition in CamelCase or in foo.example.com/CamelCase.
+                      maxLength: 316
+                      pattern: ^([a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*/)?(([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9])$
+                      type: string
+                  required:
+                  - lastTransitionTime
+                  - message
+                  - reason
+                  - status
+                  - type
+                  type: object
+                type: array
               inUseCount:
                 description: |-
                   InUseCount is the number of GameServers currently referencing
diff --git a/operator/config/rbac/role.yaml b/operator/config/rbac/role.yaml
index 56a8d282d..e9d3d9337 100644
--- a/operator/config/rbac/role.yaml
+++ b/operator/config/rbac/role.yaml
@@ -8,16 +8,13 @@ rules:
   - ""
   resources:
   - configmaps
-  - persistentvolumeclaims
-  - pods
-  - pods/ephemeralcontainers
-  - pods/log
-  - secrets
-  - serviceaccounts
-  - services
   verbs:
+  - create
+  - delete
   - get
   - list
+  - patch
+  - update
   - watch
 - apiGroups:
   - ""
@@ -29,6 +26,20 @@ rules:
   - list
   - patch
   - watch
+- apiGroups:
+  - ""
+  resources:
+  - persistentvolumeclaims
+  - pods
+  - pods/ephemeralcontainers
+  - pods/log
+  - secrets
+  - serviceaccounts
+  - services
+  verbs:
+  - get
+  - list
+  - watch
 - apiGroups:
   - apps
   resources:
diff --git a/operator/go.mod b/operator/go.mod
index 4f1ed6b0a..2087fe0e1 100644
--- a/operator/go.mod
+++ b/operator/go.mod
@@ -13,7 +13,12 @@ require (
 // both inside the workspace (go.work) and in standalone module/Docker builds.
 replace github.com/GameplanePanel/gameplane/netguard => ../netguard
 
+// i18n is an in-repo module (no published version); resolve it locally
+// both inside the go.work workspace and in standalone/Docker builds.
+replace github.com/GameplanePanel/gameplane/i18n => ../i18n
+
 require (
+	github.com/GameplanePanel/gameplane/i18n v0.0.0
 	github.com/go-git/go-billy/v5 v5.9.2
 	github.com/go-git/go-git/v5 v5.19.3
 	github.com/go-logr/logr v1.4.4
diff --git a/operator/hack/condition-ids/main.go b/operator/hack/condition-ids/main.go
new file mode 100644
index 000000000..bbc45ec36
--- /dev/null
+++ b/operator/hack/condition-ids/main.go
@@ -0,0 +1,483 @@
+// Command condition-ids writes the English language-pack entries for operator
+// condition messages (ids condition.<type>.<reason>, lower-cased) into the
+// shared English reference, and guards that every reason the controllers can
+// write has an entry.
+//
+// The table below is the source of truth for the English text. The guard
+// scans the controllers' Go source for the reason literals they set and fails
+// when a reason is missing from the table, or when a table reason is no longer
+// set anywhere. It reports the mismatch instead of editing the table.
+package main
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"os"
+	"path/filepath"
+	"sort"
+	"strconv"
+	"strings"
+
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+)
+
+// reqExpr is the ICU select that names an AddressAssignment request. The table
+// writes it as $REQ.
+const reqExpr = "{requestKind, select, addressAndPool {address ''{address}'' from pool ''{pool}''} address {address ''{address}''} other {pool ''{pool}''}}"
+
+// row is one table entry. types lists the condition types that share the
+// text (for example Ready|Pulling). dynamic rows take their reason from a
+// runtime phase string, so the guard does not require them in the source.
+type row struct {
+	types       []string
+	reason      string
+	english     string
+	description string
+	dynamic     bool
+}
+
+// guardCalls maps a helper that takes a condition reason as a string literal
+// to the index of that argument.
+var guardCalls = map[string]int{
+	"markUnhealthy":                 2,
+	"markFailed":                    2,
+	"markPending":                   2,
+	"failWithReason":                2,
+	"setSnapshotForgottenCondition": 3,
+}
+
+// guardReturnFuncs are the functions whose first string result is a reason.
+var guardReturnFuncs = map[string]bool{
+	"waitingReason":      true,
+	"provisioningReason": true,
+	"containerFailure":   true,
+}
+
+// guardSkipFiles are controller files whose Reason is free text.
+var guardSkipFiles = map[string]bool{
+	"gameserver_idle.go": true,
+}
+
+// rows is the English reference for every condition reason.
+var rows = []row{
+	// GameServer: Ready
+	{types: []string{"Ready"}, reason: "Running", english: "The server is running and the agent is reporting heartbeats.", description: "Ready condition while the game server is up."},
+	{types: []string{"Ready"}, reason: "Pending", english: "The server is waiting to start.", description: "Ready condition while the game server is being created."},
+	{types: []string{"Ready"}, reason: "Starting", english: "The server is starting.", description: "Ready condition while the pod is starting up."},
+	{types: []string{"Ready"}, reason: "Stopping", english: "The server is stopping.", description: "Ready condition while the pod is shutting down."},
+	{types: []string{"Ready"}, reason: "Suspended", english: "The server is stopped.", description: "Ready condition for a server that was stopped."},
+	{types: []string{"Ready"}, reason: "IdleAsleep", english: "The server is asleep because no players are online.", description: "Ready condition for a server put to sleep by idle auto-sleep."},
+	{types: []string{"Ready"}, reason: "Failed", english: "{detail}", description: "Ready condition when the server cannot start. detail is the English reason from the operator, for example a missing template or an invalid configuration."},
+	{types: []string{"Ready"}, reason: "Unknown", english: "The state of the server is not known yet.", description: "Ready condition before the operator has observed the server."},
+	{types: []string{"Ready"}, reason: "PVCProvisioningFailed", english: "Storage cannot be provisioned: PVC ''{pvc}'' needs StorageClass ''{storageClass}'', which does not exist on this cluster.", description: "Ready condition when the data volume cannot be created. pvc is the volume claim name, storageClass the missing class."},
+	{types: []string{"Ready"}, reason: "ImagePullFailed", english: "The game image cannot be pulled. Check the image reference.", description: "Ready condition when the container image pull keeps failing."},
+	{types: []string{"Ready"}, reason: "CrashLoopBackOff", english: "The game container keeps crashing during startup ({restartCount} restarts so far). Check the logs.", description: "Ready condition when the game container crash-loops. restartCount is the number of restarts."},
+	{types: []string{"Ready"}, reason: "ContainerExited", english: "The game container exited with code {exitCode} during startup. Check the logs.", description: "Ready condition when the game container exits during startup. exitCode is the process exit code."},
+
+	// GameServer: Progressing
+	{types: []string{"Progressing"}, reason: "Stable", english: "The server is stable and nothing is changing.", description: "Progressing condition once the server is running."},
+	{types: []string{"Progressing"}, reason: "Pending", english: "The server is waiting to be scheduled.", description: "Progressing condition while the pod is waiting for a node."},
+	{types: []string{"Progressing"}, reason: "Starting", english: "The server is starting.", description: "Progressing condition while the pod starts."},
+	{types: []string{"Progressing"}, reason: "Stopping", english: "The server is stopping.", description: "Progressing condition while the pod stops."},
+	{types: []string{"Progressing"}, reason: "Suspended", english: "The server is stopped and nothing is in progress.", description: "Progressing condition for a stopped server."},
+	{types: []string{"Progressing"}, reason: "IdleAsleep", english: "The server is asleep because no players are online.", description: "Progressing condition for an idle-sleeping server."},
+	{types: []string{"Progressing"}, reason: "Failed", english: "The server stopped trying to start.", description: "Progressing condition when startup has failed."},
+	{types: []string{"Progressing"}, reason: "Unknown", english: "The state of the server is not known yet.", description: "Progressing condition before the operator has observed the server."},
+	{types: []string{"Progressing"}, reason: "PVCProvisioningFailed", english: "Storage cannot be provisioned: PVC ''{pvc}'' needs StorageClass ''{storageClass}'', which does not exist on this cluster.", description: "Progressing condition when the data volume cannot be created. pvc is the volume claim name, storageClass the missing class."},
+	{types: []string{"Progressing"}, reason: "ImagePullFailed", english: "The game image cannot be pulled. Check the image reference.", description: "Progressing condition when the container image pull keeps failing."},
+	{types: []string{"Progressing"}, reason: "CrashLoopBackOff", english: "The game container keeps crashing during startup ({restartCount} restarts so far). Check the logs.", description: "Progressing condition when the game container crash-loops. restartCount is the number of restarts."},
+	{types: []string{"Progressing"}, reason: "ContainerExited", english: "The game container exited with code {exitCode} during startup. Check the logs.", description: "Progressing condition when the game container exits during startup. exitCode is the process exit code."},
+	{types: []string{"Progressing"}, reason: "PullingImage", english: "Pulling the game image.", description: "Progressing detail while the container image downloads."},
+	{types: []string{"Progressing"}, reason: "ContainerCreating", english: "Creating the container.", description: "Progressing detail while the kubelet creates the container."},
+	{types: []string{"Progressing"}, reason: "WaitingForAgent", english: "The server is up. Waiting for the first heartbeat from the agent.", description: "Progressing detail once the game container runs but the agent has not reported yet."},
+	{types: []string{"Progressing"}, reason: "InstallingServerFiles", english: "Downloading game files or waiting for the server to become ready.", description: "Progressing detail during first-run installation."},
+
+	// GameServer: Healthy
+	{types: []string{"Healthy"}, reason: "AgentFresh", english: "The agent is reporting heartbeats.", description: "Healthy condition while heartbeats arrive."},
+	{types: []string{"Healthy"}, reason: "AgentStale", english: "The agent has not reported a heartbeat recently.", description: "Healthy condition when heartbeats stopped."},
+	{types: []string{"Healthy"}, reason: "Pending", english: "The server has not started yet.", description: "Healthy condition before the first start."},
+	{types: []string{"Healthy"}, reason: "Stopping", english: "The server is stopping.", description: "Healthy condition while stopping."},
+	{types: []string{"Healthy"}, reason: "Suspended", english: "The server is stopped.", description: "Healthy condition for a stopped server."},
+	{types: []string{"Healthy"}, reason: "IdleAsleep", english: "The server is asleep because no players are online.", description: "Healthy condition for an idle-sleeping server."},
+	{types: []string{"Healthy"}, reason: "Failed", english: "The server failed.", description: "Healthy condition when the server has failed."},
+	{types: []string{"Healthy"}, reason: "Unknown", english: "The state of the server is not known yet.", description: "Healthy condition before the operator has observed the server."},
+
+	// GameServer: AddressAssignment ($REQ is the request phrase, see reqExpr)
+	{types: []string{"AddressAssignment"}, reason: "IgnoredForExposureMode", english: "Requested $REQ is ignored: it applies only to the LoadBalancer expose mode, and this server is exposed as ''{expose}''.", description: "AddressAssignment condition when an address or pool is requested for a server that is not exposed as a LoadBalancer. expose is the current expose mode."},
+	{types: []string{"AddressAssignment"}, reason: "InvalidAddress", english: "The requested address ''{address}'' is not a valid IP address.", description: "AddressAssignment condition when the requested address does not parse."},
+	{types: []string{"AddressAssignment"}, reason: "NoAddressManagerConfigured", english: "Requested $REQ cannot be honored: this cluster has no load-balancer address manager configured, so any address comes from the default assignment policy.", description: "AddressAssignment condition when no address manager (MetalLB or Cilium) is configured."},
+	{types: []string{"AddressAssignment"}, reason: "AddressInUse", english: "The requested address ''{address}'' is already in use by GameServer ''{server}''.", description: "AddressAssignment condition when another game server holds the requested address."},
+	{types: []string{"AddressAssignment"}, reason: "PoolNotFound", english: "The requested address pool ''{pool}'' was not found.", description: "AddressAssignment condition when the requested address pool does not exist."},
+	{types: []string{"AddressAssignment"}, reason: "AllocationFailed", english: "The address manager could not allocate an address: {detail}", description: "AddressAssignment condition when the address manager reports an allocation failure. detail is the address manager's own English message."},
+	{types: []string{"AddressAssignment"}, reason: "ServiceNotReady", english: "Requested $REQ: waiting for the LoadBalancer Service that carries the request to exist.", description: "AddressAssignment condition before the load-balancer Service exists."},
+	{types: []string{"AddressAssignment"}, reason: "AssignmentPending", english: "Requested $REQ: the address manager has not assigned an address yet.", description: "AddressAssignment condition while the address manager works."},
+	{types: []string{"AddressAssignment"}, reason: "Assigned", english: "{assignedFrom, select, pool {Address {address} assigned from pool ''{pool}''.} other {Address {address} assigned.}}", description: "AddressAssignment condition once an address is assigned. assignedFrom is pool or default."},
+
+	// GameServer: tunnel and other
+	{types: []string{"TunnelReady"}, reason: "InvalidConfig", english: "{provider, select, none {The tunnel is enabled but the server has no tunnel configuration.} other {The ''{provider}'' tunnel provider is selected but its configuration is missing.}}", description: "TunnelReady condition for an incomplete tunnel setup. provider is the selected provider, or none."},
+	{types: []string{"TunnelReady"}, reason: "DeploymentNotReady", english: "Waiting for the tunnel deployment to become ready.", description: "TunnelReady condition while the tunnel pod is not ready."},
+	{types: []string{"TunnelReady"}, reason: "PortNotMapped", english: "No frp remote port is configured for: {ports}.", description: "TunnelReady condition for frp when advertised ports have no remote port. ports is a comma-separated list of port names."},
+	{types: []string{"TunnelReady"}, reason: "NoCredentials", english: "No credentials secret was provided, so the ''{provider}'' tunnel cannot authenticate.", description: "TunnelReady condition when a tunnel provider needs credentials that are missing."},
+	{types: []string{"TunnelReady"}, reason: "Ready", english: "{provider, select, playit {The tunnel deployment is ready. Waiting for the playit endpoint assignment.} tailscale {The tunnel deployment is ready and authenticated.} other {The tunnel deployment is ready and all ports are mapped.}}", description: "TunnelReady condition when the tunnel works."},
+	{types: []string{"TunnelReady"}, reason: "UnknownProvider", english: "Unknown tunnel provider ''{provider}''.", description: "TunnelReady condition when the provider name is not supported."},
+	{types: []string{"TunnelReady"}, reason: "TunnelCredentialRefused", english: "The tunnel credentials secret ''{secret}'' is not owned by this GameServer. {remedy, select, defaultName {Add an ownerReference to this GameServer to the Secret, or delete the Secret and save the credential again from the dashboard.} other {Save the credential from the dashboard, or add an ownerReference to this GameServer to the Secret.}}", description: "TunnelReady condition when the operator refuses to mount a credentials secret. secret is the secret name, remedy is defaultName or other."},
+	{types: []string{"TunnelHostnameIgnored"}, reason: "SettingIgnored", english: "These settings apply to the backing Service, not to tunnel traffic: {settings}.", description: "Informational condition when hostname, source ranges or node ports are set on a server with a tunnel. settings is a comma-separated list of field names."},
+	{types: []string{"TunnelAddressInvalid"}, reason: "ValidationFailed", english: "Some tunnel endpoints were rejected: {details}", description: "Condition when endpoints reported by the playit tunnel pod fail validation. details is the English validation text."},
+	{types: []string{"IdleScheduleInvalid"}, reason: "WakeWindowUnparseable", english: "A wake window in the idle schedule cannot be parsed: {details}", description: "Condition when spec.idle has an invalid wake window. details is the English parse error."},
+	{types: []string{"DataWipe"}, reason: "JobFailed", english: "The data wipe job did not complete. The volume may not be fully cleared.", description: "DataWipe condition when the wipe job fails."},
+
+	// Backup, Restore, Unquiesced, SnapshotForgotten (Type Completed is shared)
+	{types: []string{"Completed"}, reason: "Succeeded", english: "The backup or restore completed successfully.", description: "Completed condition on a Backup or Restore that finished."},
+	{types: []string{"Completed"}, reason: "Failed", english: "The backup or restore failed.", description: "Completed condition on a Backup or Restore that failed. The message holds the English detail."},
+	{types: []string{"Completed"}, reason: "JobFailed", english: "The backup job reported a failure.", description: "Completed condition on a Backup whose job failed."},
+	{types: []string{"Completed"}, reason: "Pending", english: "The backup is waiting to start.", description: "Completed condition on a Backup that has not started (dynamic: reason is the phase).", dynamic: true},
+	{types: []string{"Completed"}, reason: "Running", english: "The backup is running.", description: "Completed condition on a Backup in progress (dynamic: reason is the phase).", dynamic: true},
+	{types: []string{"Unquiesced"}, reason: "Unquiesced", english: "The server was resumed after the backup.", description: "Unquiesced condition when the world was unfrozen."},
+	{types: []string{"Unquiesced"}, reason: "Failed", english: "The server could not be resumed after the backup. Its world may still have auto-save turned off.", description: "Unquiesced condition when the unfreeze failed."},
+	{types: []string{"SnapshotForgotten"}, reason: "Forgotten", english: "The snapshot was removed from the backup repository.", description: "SnapshotForgotten condition after a deleted Backup's snapshot was forgotten."},
+	{types: []string{"SnapshotForgotten"}, reason: "ForgetAbandoned", english: "The snapshot was not removed from the backup repository when the backup was deleted.", description: "SnapshotForgotten condition when the forget step was abandoned."},
+
+	// BackupSchedule
+	{types: []string{"ScheduleValid"}, reason: "CronParseError", english: "The schedule is not a valid cron expression.", description: "ScheduleValid condition for an unparseable schedule."},
+	{types: []string{"ScheduleValid"}, reason: "CronValid", english: "The schedule is a valid cron expression.", description: "ScheduleValid condition for a good schedule."},
+	{types: []string{"RetentionTrimmed"}, reason: "TrimFailed", english: "Applying the retention policy failed.", description: "RetentionTrimmed condition when old backups could not be removed."},
+	{types: []string{"RetentionTrimmed"}, reason: "TrimSucceeded", english: "The retention policy was applied.", description: "RetentionTrimmed condition after a successful trim."},
+
+	// Cluster (Type Healthy; no overlap with the GameServer Healthy reasons)
+	{types: []string{"Healthy"}, reason: "HealthCheckPassed", english: "The cluster is reachable and healthy.", description: "Healthy condition on a registered cluster."},
+	{types: []string{"Healthy"}, reason: "NameReserved", english: "The cluster name \"local\" is reserved.", description: "Healthy condition when a cluster is registered with the reserved name."},
+	{types: []string{"Healthy"}, reason: "SecretNotFound", english: "The kubeconfig secret was not found.", description: "Healthy condition when the kubeconfig secret is missing."},
+	{types: []string{"Healthy"}, reason: "InvalidSecret", english: "The kubeconfig secret is missing the required label.", description: "Healthy condition when the secret lacks the cluster-kubeconfig label."},
+	{types: []string{"Healthy"}, reason: "MissingKey", english: "The kubeconfig secret does not contain the expected key.", description: "Healthy condition when the kubeconfig key is absent."},
+	{types: []string{"Healthy"}, reason: "BadKubeconfig", english: "The kubeconfig could not be used.", description: "Healthy condition when the kubeconfig does not parse."},
+	{types: []string{"Healthy"}, reason: "DiscoveryClientFailed", english: "Connecting to the cluster failed.", description: "Healthy condition when the discovery client cannot be built."},
+	{types: []string{"Healthy"}, reason: "HealthCheckFailed", english: "The cluster health check failed.", description: "Healthy condition when the cluster does not answer."},
+
+	// Module (failure reasons are also written on Type Pulling)
+	{types: []string{"Ready"}, reason: "Applied", english: "The module template was applied.", description: "Ready condition on a Module after its GameTemplate was written."},
+	{types: []string{"Ready"}, reason: "InUse", english: "The module cannot be removed while game servers use its template.", description: "Ready condition when deletion is blocked."},
+	{types: []string{"Ready", "Pulling"}, reason: "SourceNotFound", english: "The module source was not found.", description: "Module condition when the named ModuleSource does not exist."},
+	{types: []string{"Ready", "Pulling"}, reason: "WaitingForCatalog", english: "Waiting for the module source to index this module.", description: "Module condition while the source has no catalog entry yet."},
+	{types: []string{"Ready", "Pulling"}, reason: "NoVersionAvailable", english: "The module source has no available versions.", description: "Module condition when no version can be chosen."},
+	{types: []string{"Ready", "Pulling"}, reason: "VersionUnavailable", english: "The requested version is not in the catalog.", description: "Module condition when the pinned version is missing."},
+	{types: []string{"Ready", "Pulling"}, reason: "SourceConfig", english: "The module source configuration is invalid.", description: "Module condition for a broken source setup."},
+	{types: []string{"Ready", "Pulling"}, reason: "PullFailed", english: "Pulling the module failed.", description: "Module condition when the OCI pull fails."},
+	{types: []string{"Ready", "Pulling"}, reason: "VerifyConfig", english: "The signature verification settings are invalid.", description: "Module condition for a bad verification setup."},
+	{types: []string{"Ready", "Pulling"}, reason: "SignatureInvalid", english: "The module signature could not be verified.", description: "Module condition when cosign verification fails."},
+	{types: []string{"Ready", "Pulling"}, reason: "DigestMismatch", english: "The module content does not match its pinned digest.", description: "Module condition when the digest differs from the pin."},
+	{types: []string{"Ready", "Pulling"}, reason: "IncompatibleOperator", english: "The module needs a newer Gameplane operator.", description: "Module condition when gameplaneMinVersion is not met."},
+	{types: []string{"Ready", "Pulling"}, reason: "ApplyTemplate", english: "Applying the module template failed.", description: "Module condition when the GameTemplate cannot be written."},
+	{types: []string{"Pulling"}, reason: "Pulling", english: "Pulling the module.", description: "Pulling condition while a pull runs."},
+	{types: []string{"Pulling"}, reason: "Applied", english: "The module pull finished.", description: "Pulling condition once the template was applied."},
+	{types: []string{"LocalesValid"}, reason: "Valid", english: "All module translations are valid.", description: "LocalesValid condition on a GameTemplate when every translation entry shipped with the module is valid."},
+	{types: []string{"LocalesValid"}, reason: "InvalidEntries", english: "Some module translation entries are invalid and were left out.", description: "LocalesValid condition on a GameTemplate when translation entries or files were dropped. The message holds the English per-language counts."},
+	{types: []string{"LocalesValid"}, reason: "LocalesTooLarge", english: "Some module translations were left out because they are too large.", description: "LocalesValid condition on a GameTemplate when a language file is over the size limit or the translations together exceed it. The message names the languages."},
+	{types: []string{"LocalesValid"}, reason: "WriteFailed", english: "Module translations could not be stored.", description: "LocalesValid condition on a GameTemplate when the translations ConfigMap could not be written. The message holds the English error."},
+
+	// ModuleSource
+	{types: []string{"Synced"}, reason: "Indexed", english: "The module source was indexed.", description: "Synced condition after a successful index."},
+	{types: []string{"Synced"}, reason: "IndexFailed", english: "Indexing the module source failed.", description: "Synced condition after a failed index."},
+	{types: []string{"Ready"}, reason: "CatalogPopulated", english: "The module catalog is populated.", description: "Ready condition on a source with a catalog."},
+	{types: []string{"Ready"}, reason: "SourceUnreachable", english: "The module source has never been indexed successfully.", description: "Ready condition on a source that cannot be reached."},
+	{types: []string{"Ready"}, reason: "ServingStaleCatalog", english: "Serving the cached catalog. The last index attempt failed.", description: "Ready condition while an older catalog stays available."},
+
+	// NetworkCapture
+	{types: []string{"Failed"}, reason: "failed", english: "The capture failed.", description: "Failed condition on a NetworkCapture; the message holds the English detail."},
+	{types: []string{"Failed"}, reason: "capture_already_in_progress", english: "Another capture is already running on this server.", description: "Failed condition when two captures target one server."},
+	{types: []string{"Failed"}, reason: "PodRestarted", english: "The game pod restarted while the capture was running.", description: "Failed condition when the pod was replaced during a capture."},
+	{types: []string{"Failed"}, reason: "SidecarCrashed", english: "The capture sidecar exited unexpectedly.", description: "Failed condition when the capture container died."},
+	{types: []string{"SidecarStopFailed"}, reason: "sidecar_stop_failed", english: "Stopping the capture sidecar failed.", description: "Condition when the stop request to the sidecar failed."},
+	{types: []string{"RetentionStopFailed"}, reason: "sidecar_stop_failed", english: "Stopping the capture sidecar at the end of retention failed.", description: "Condition when the retention-expiry stop failed."},
+	{types: []string{"FileCleanupFailed"}, reason: "delete_failed", english: "Deleting the capture file failed. It may stay past its retention.", description: "Condition when the capture file could not be deleted."},
+	{types: []string{"SidecarStopped"}, reason: "stopped", english: "The capture sidecar was told to stop.", description: "SidecarStopped condition after a stop request."},
+	{types: []string{"SidecarStopped"}, reason: "never_started", english: "The capture was stopped before it started.", description: "SidecarStopped condition when a pending capture was cancelled."},
+}
+
+// entry is one generated pack entry with its condition id.
+type entry struct {
+	id    string
+	value pack.Entry
+}
+
+func main() {
+	app := flag.String("app", "../i18n/locales/en/app.json", "English reference app.json to update")
+	controllers := flag.String("controllers", "internal/controller", "controller package directory scanned by the coverage guard")
+	check := flag.Bool("check", false, "report drift against the table and exit 1 instead of writing")
+	flag.Parse()
+
+	if err := run(*app, *controllers, *check); err != nil {
+		fmt.Fprintln(os.Stderr, "condition-ids:", err)
+		os.Exit(1)
+	}
+}
+
+func run(appPath, controllersDir string, check bool) error {
+	entries, err := generate()
+	if err != nil {
+		return err
+	}
+	if err := guardReasons(controllersDir); err != nil {
+		return err
+	}
+
+	appPath = filepath.Clean(appPath)
+	data, err := os.ReadFile(appPath)
+	if err != nil {
+		return fmt.Errorf("read %s: %w", appPath, err)
+	}
+	existing, err := pack.ParseEntries(data)
+	if err != nil {
+		return fmt.Errorf("parse %s: %w", appPath, err)
+	}
+
+	if check {
+		return checkDrift(existing, entries)
+	}
+
+	for id := range existing {
+		if strings.HasPrefix(id, "condition.") {
+			delete(existing, id)
+		}
+	}
+	for _, e := range entries {
+		existing[e.id] = e.value
+	}
+	out, err := pack.Marshal(existing)
+	if err != nil {
+		return err
+	}
+	if err := writeInDir(filepath.Dir(appPath), filepath.Base(appPath), out); err != nil {
+		return fmt.Errorf("write %s: %w", appPath, err)
+	}
+	fmt.Printf("condition-ids: wrote %d condition.* ids to %s\n", len(entries), appPath)
+	return nil
+}
+
+// generate expands the table into one entry per (type, reason) pair.
+func generate() ([]entry, error) {
+	var out []entry
+	seen := map[string]bool{}
+	for _, r := range rows {
+		text := strings.ReplaceAll(r.english, "$REQ", reqExpr)
+		for _, t := range r.types {
+			id := "condition." + strings.ToLower(t) + "." + strings.ToLower(r.reason)
+			if seen[id] {
+				return nil, fmt.Errorf("duplicate id %s in table", id)
+			}
+			seen[id] = true
+			out = append(out, entry{id: id, value: pack.Entry{DefaultMessage: text, Description: r.description}})
+		}
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].id < out[j].id })
+	return out, nil
+}
+
+// checkDrift compares the condition.* ids in the English reference with the
+// table. Any missing, extra or changed id is reported and returned as an error.
+func checkDrift(existing map[string]pack.Entry, entries []entry) error {
+	var problems []string
+	want := map[string]bool{}
+	for _, e := range entries {
+		want[e.id] = true
+		got, ok := existing[e.id]
+		switch {
+		case !ok:
+			problems = append(problems, "missing "+e.id)
+		case got.DefaultMessage != e.value.DefaultMessage || got.Description != e.value.Description:
+			problems = append(problems, "changed "+e.id)
+		}
+	}
+	for id := range existing {
+		if strings.HasPrefix(id, "condition.") && !want[id] {
+			problems = append(problems, "extra "+id)
+		}
+	}
+	if len(problems) == 0 {
+		return nil
+	}
+	sort.Strings(problems)
+	return fmt.Errorf("condition ids drift from the table (run make i18n-sync):\n  %s", strings.Join(problems, "\n  "))
+}
+
+// guardReasons parses the non-test controller sources and checks that the
+// reason literals they set match the table's reason set in both directions.
+func guardReasons(dir string) error {
+	found, err := collectReasons(dir)
+	if err != nil {
+		return err
+	}
+	tableReasons := map[string]bool{}
+	for _, r := range rows {
+		tableReasons[r.reason] = true
+	}
+
+	var errs []error
+	var unknown []string
+	for reason, pos := range found {
+		if !tableReasons[reason] {
+			unknown = append(unknown, fmt.Sprintf("%s: reason %q has no condition table entry", pos, reason))
+		}
+	}
+	sort.Strings(unknown)
+	for _, u := range unknown {
+		errs = append(errs, errors.New(u))
+	}
+	for _, r := range rows {
+		if r.dynamic {
+			continue
+		}
+		if _, ok := found[r.reason]; !ok {
+			errs = append(errs, fmt.Errorf("table reason %q (%s) is not set by any controller file", r.reason, strings.Join(r.types, "|")))
+		}
+	}
+	if len(errs) == 0 {
+		return nil
+	}
+	msgs := make([]string, 0, len(errs))
+	for _, e := range errs {
+		msgs = append(msgs, e.Error())
+	}
+	return fmt.Errorf("coverage guard mismatch (report the diff, do not edit the table silently):\n  %s", strings.Join(msgs, "\n  "))
+}
+
+// collectReasons returns the first position of every non-empty reason literal
+// the controllers can write.
+func collectReasons(dir string) (map[string]string, error) {
+	dir = filepath.Clean(dir)
+	dirEntries, err := os.ReadDir(dir)
+	if err != nil {
+		return nil, fmt.Errorf("read controllers dir %s: %w", dir, err)
+	}
+	fset := token.NewFileSet()
+	found := map[string]string{}
+	record := func(lit *ast.BasicLit, path string) {
+		if lit == nil || lit.Kind != token.STRING {
+			return
+		}
+		v, err := strconv.Unquote(lit.Value)
+		if err != nil || v == "" {
+			return
+		}
+		if _, ok := found[v]; !ok {
+			found[v] = fmt.Sprintf("%s:%d", path, fset.Position(lit.Pos()).Line)
+		}
+	}
+	for _, de := range dirEntries {
+		name := de.Name()
+		if de.IsDir() || !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") || guardSkipFiles[name] {
+			continue
+		}
+		path := filepath.Join(dir, name)
+		file, err := parser.ParseFile(fset, path, nil, 0)
+		if err != nil {
+			return nil, fmt.Errorf("parse %s: %w", path, err)
+		}
+		collectFile(file, path, record)
+	}
+	return found, nil
+}
+
+// collectFile applies the guard's collection rules to one parsed file.
+func collectFile(file *ast.File, path string, record func(*ast.BasicLit, string)) {
+	for _, decl := range file.Decls {
+		switch d := decl.(type) {
+		case *ast.GenDecl:
+			// Rule 4: the PVC provisioning reason constant.
+			for _, spec := range d.Specs {
+				vs, ok := spec.(*ast.ValueSpec)
+				if !ok {
+					continue
+				}
+				for i, name := range vs.Names {
+					if name.Name == "GameServerConditionReasonPVCProvisioningFailed" && i < len(vs.Values) {
+						if lit, ok := vs.Values[i].(*ast.BasicLit); ok {
+							record(lit, path)
+						}
+					}
+				}
+			}
+		case *ast.FuncDecl:
+			// Rule 5: first string result of the pod-reason helpers.
+			if d.Body != nil && guardReturnFuncs[d.Name.Name] {
+				ast.Inspect(d.Body, func(n ast.Node) bool {
+					ret, ok := n.(*ast.ReturnStmt)
+					if !ok || len(ret.Results) == 0 {
+						return true
+					}
+					if lit, ok := ret.Results[0].(*ast.BasicLit); ok {
+						record(lit, path)
+					}
+					return true
+				})
+			}
+		}
+	}
+
+	ast.Inspect(file, func(n ast.Node) bool {
+		switch x := n.(type) {
+		case *ast.KeyValueExpr:
+			// Rule 1: composite-literal keys named Reason or reason.
+			if key, ok := x.Key.(*ast.Ident); ok && (key.Name == "Reason" || key.Name == "reason") {
+				if lit, ok := x.Value.(*ast.BasicLit); ok {
+					record(lit, path)
+				}
+			}
+		case *ast.AssignStmt:
+			// Rule 2: .Reason / .reason / readyReason assigned a literal.
+			if len(x.Lhs) != len(x.Rhs) {
+				return true
+			}
+			for i, lhs := range x.Lhs {
+				lit, ok := x.Rhs[i].(*ast.BasicLit)
+				if !ok {
+					continue
+				}
+				switch l := lhs.(type) {
+				case *ast.SelectorExpr:
+					if l.Sel.Name == "Reason" || l.Sel.Name == "reason" {
+						record(lit, path)
+					}
+				case *ast.Ident:
+					if l.Name == "readyReason" {
+						record(lit, path)
+					}
+				}
+			}
+		case *ast.CallExpr:
+			// Rule 3: the reason argument of the status helpers.
+			name := ""
+			switch f := x.Fun.(type) {
+			case *ast.Ident:
+				name = f.Name
+			case *ast.SelectorExpr:
+				name = f.Sel.Name
+			}
+			idx, ok := guardCalls[name]
+			if !ok || len(x.Args) <= idx {
+				return true
+			}
+			if lit, ok := x.Args[idx].(*ast.BasicLit); ok {
+				record(lit, path)
+			}
+		}
+		return true
+	})
+}
+
+// writeInDir writes name inside dir through an os.Root, so the write cannot
+// escape dir.
+func writeInDir(dir, name string, data []byte) error {
+	root, err := os.OpenRoot(dir)
+	if err != nil {
+		return fmt.Errorf("open %s: %w", dir, err)
+	}
+	defer func() { _ = root.Close() }()
+	if err := root.WriteFile(name, data, 0o600); err != nil {
+		return fmt.Errorf("write %s: %w", name, err)
+	}
+	return nil
+}
diff --git a/operator/internal/controller/gameserver_condition_args.go b/operator/internal/controller/gameserver_condition_args.go
new file mode 100644
index 000000000..f650c057f
--- /dev/null
+++ b/operator/internal/controller/gameserver_condition_args.go
@@ -0,0 +1,218 @@
+package controller
+
+import (
+	"strconv"
+	"strings"
+
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+
+	gameplanev1alpha1 "github.com/GameplanePanel/gameplane/operator/api/v1alpha1"
+)
+
+// setConditionArgs replaces the args of one condition type. Empty args delete
+// the entry; an empty map becomes nil so omitempty drops the field.
+func setConditionArgs(st *gameplanev1alpha1.GameServerStatus, condType string, args map[string]string) {
+	if len(args) == 0 {
+		delete(st.ConditionArgs, condType)
+		if len(st.ConditionArgs) == 0 {
+			st.ConditionArgs = nil
+		}
+		return
+	}
+	if st.ConditionArgs == nil {
+		st.ConditionArgs = map[string]map[string]string{}
+	}
+	st.ConditionArgs[condType] = args
+}
+
+// conditionArgsInput is what reconcileStatus knows when it derives the map.
+type conditionArgsInput struct {
+	prov         *provisioningInfo // may be nil
+	plan         addressPlan
+	assigned     string // loadBalancerAddress(svcPtr)
+	conflicting  string // conflictingServer
+	tunnelPlan   tunnelPlan
+	playitErr    string // errMsg from validatePlayitEndpoints ("" when none)
+	idleSchedErr error
+}
+
+// deriveConditionArgs walks gs.Status.Conditions and returns the new map (nil when empty).
+func deriveConditionArgs(gs *gameplanev1alpha1.GameServer, in conditionArgsInput) map[string]map[string]string {
+	var out map[string]map[string]string
+	for i := range gs.Status.Conditions {
+		cond := &gs.Status.Conditions[i]
+		args := conditionArgsFor(gs, cond, in)
+		if len(args) == 0 {
+			continue
+		}
+		if out == nil {
+			out = map[string]map[string]string{}
+		}
+		out[cond.Type] = args
+	}
+	return out
+}
+
+// conditionArgsFor returns the args of one condition's current reason, or nil
+// when that (type, reason) pair has no localized arguments.
+func conditionArgsFor(gs *gameplanev1alpha1.GameServer, cond *metav1.Condition, in conditionArgsInput) map[string]string {
+	if (cond.Type == "Ready" || cond.Type == "Progressing") && in.prov != nil &&
+		cond.Reason == in.prov.reason && len(in.prov.args) > 0 {
+		return in.prov.args
+	}
+	switch cond.Type {
+	case "Ready":
+		if cond.Reason == "Failed" {
+			return map[string]string{"detail": cond.Message}
+		}
+	case gameplanev1alpha1.GameServerConditionAddressAssignment:
+		return addressConditionArgs(gs, cond, in)
+	case "TunnelReady":
+		switch cond.Reason {
+		case "InvalidConfig", "NoCredentials", "Ready", "UnknownProvider":
+			return map[string]string{"provider": tunnelProviderArg(gs)}
+		case "PortNotMapped":
+			return map[string]string{"ports": strings.Join(in.tunnelPlan.noMapping, ", ")}
+		}
+	case "TunnelHostnameIgnored":
+		if cond.Reason == "SettingIgnored" {
+			return map[string]string{"settings": strings.Join(ignoredTunnelSettings(gs), ", ")}
+		}
+	case "TunnelAddressInvalid":
+		if cond.Reason == "ValidationFailed" {
+			return map[string]string{"details": in.playitErr}
+		}
+	case "IdleScheduleInvalid":
+		if cond.Reason == "WakeWindowUnparseable" && in.idleSchedErr != nil {
+			return map[string]string{"details": in.idleSchedErr.Error()}
+		}
+	}
+	return nil
+}
+
+// addressConditionArgs returns the args of an AddressAssignment reason.
+func addressConditionArgs(gs *gameplanev1alpha1.GameServer, cond *metav1.Condition, in conditionArgsInput) map[string]string {
+	plan := in.plan
+	switch cond.Reason {
+	case "IgnoredForExposureMode":
+		expose := gs.Spec.Networking.Expose
+		if expose == "" {
+			expose = "ClusterIP"
+		}
+		return map[string]string{
+			"requestKind": addressRequestKind(plan),
+			"address":     plan.Address,
+			"pool":        plan.Pool,
+			"expose":      expose,
+		}
+	case "InvalidAddress":
+		return map[string]string{"address": gs.Spec.Networking.Address}
+	case "NoAddressManagerConfigured", "ServiceNotReady", "AssignmentPending":
+		return map[string]string{
+			"requestKind": addressRequestKind(plan),
+			"address":     plan.Address,
+			"pool":        plan.Pool,
+		}
+	case "AddressInUse":
+		return map[string]string{"address": gs.Spec.Networking.Address, "server": in.conflicting}
+	case "PoolNotFound":
+		return map[string]string{"pool": plan.Pool}
+	case "AllocationFailed":
+		return map[string]string{"detail": cond.Message}
+	case "Assigned":
+		assignedFrom := "default"
+		if plan.Pool != "" {
+			assignedFrom = "pool"
+		}
+		return map[string]string{"address": in.assigned, "pool": plan.Pool, "assignedFrom": assignedFrom}
+	}
+	return nil
+}
+
+// addressRequestKind names the shape of a pool/address request for the
+// localized REQ phrase; it mirrors addressRequestSummary.
+func addressRequestKind(plan addressPlan) string {
+	switch {
+	case plan.Pool != "" && plan.Address != "":
+		return "addressAndPool"
+	case plan.Address != "":
+		return "address"
+	default:
+		return "pool"
+	}
+}
+
+// tunnelProviderArg is the provider name the TunnelReady text names, or "none"
+// when the server has no tunnel spec.
+func tunnelProviderArg(gs *gameplanev1alpha1.GameServer) string {
+	if gs.Spec.Networking.Tunnel == nil {
+		return "none"
+	}
+	return gs.Spec.Networking.Tunnel.Provider
+}
+
+// ignoredTunnelSettings lists the networking settings that are set but do not
+// apply to tunnel traffic (they configure the backing Service instead).
+func ignoredTunnelSettings(gs *gameplanev1alpha1.GameServer) []string {
+	var ignoredSettings []string
+	if gs.Spec.Networking.Hostname != "" {
+		ignoredSettings = append(ignoredSettings, "hostname")
+	}
+	if len(gs.Spec.Networking.SourceRanges) > 0 {
+		ignoredSettings = append(ignoredSettings, "sourceRanges")
+	}
+	for _, po := range gs.Spec.Networking.PortOverrides {
+		if po.NodePort != 0 {
+			ignoredSettings = append(ignoredSettings, "nodePort")
+			break
+		}
+	}
+	return ignoredSettings
+}
+
+// provisioningArgs returns the values the localized text of a pod-derived
+// reason needs. CrashLoopBackOff: restartCount of the first init-or-game container
+// whose State.Waiting.Reason is "CrashLoopBackOff" (init containers first, then the
+// container named gameContainerName). ContainerExited: exitCode of the first
+// init-or-game container that exited non-zero, falling back to the game
+// container's terminated state. Other reasons: nil.
+func provisioningArgs(pod *corev1.Pod, reason string) map[string]string {
+	switch reason {
+	case "CrashLoopBackOff":
+		if cs := findContainerStatus(pod, func(cs *corev1.ContainerStatus) bool {
+			return cs.State.Waiting != nil && cs.State.Waiting.Reason == "CrashLoopBackOff"
+		}); cs != nil {
+			return map[string]string{"restartCount": strconv.FormatInt(int64(cs.RestartCount), 10)}
+		}
+	case "ContainerExited":
+		if cs := findContainerStatus(pod, func(cs *corev1.ContainerStatus) bool {
+			return cs.State.Terminated != nil && cs.State.Terminated.ExitCode != 0
+		}); cs != nil {
+			return map[string]string{"exitCode": strconv.FormatInt(int64(cs.State.Terminated.ExitCode), 10)}
+		}
+		for i := range pod.Status.ContainerStatuses {
+			cs := &pod.Status.ContainerStatuses[i]
+			if cs.Name == gameContainerName && cs.State.Terminated != nil {
+				return map[string]string{"exitCode": strconv.FormatInt(int64(cs.State.Terminated.ExitCode), 10)}
+			}
+		}
+	}
+	return nil
+}
+
+// findContainerStatus returns the first init container status matching match,
+// then the first game container status matching match, or nil.
+func findContainerStatus(pod *corev1.Pod, match func(*corev1.ContainerStatus) bool) *corev1.ContainerStatus {
+	for i := range pod.Status.InitContainerStatuses {
+		if cs := &pod.Status.InitContainerStatuses[i]; match(cs) {
+			return cs
+		}
+	}
+	for i := range pod.Status.ContainerStatuses {
+		if cs := &pod.Status.ContainerStatuses[i]; cs.Name == gameContainerName && match(cs) {
+			return cs
+		}
+	}
+	return nil
+}
diff --git a/operator/internal/controller/gameserver_condition_args_envtest_test.go b/operator/internal/controller/gameserver_condition_args_envtest_test.go
new file mode 100644
index 000000000..d5c602d9e
--- /dev/null
+++ b/operator/internal/controller/gameserver_condition_args_envtest_test.go
@@ -0,0 +1,176 @@
+//go:build envtest
+
+package controller
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+
+	corev1 "k8s.io/api/core/v1"
+	"k8s.io/apimachinery/pkg/api/meta"
+	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/client-go/util/retry"
+
+	gameplanev1alpha1 "github.com/GameplanePanel/gameplane/operator/api/v1alpha1"
+)
+
+// TestGameServer_ConditionArgsSetAndCleared: a missing template puts the
+// Ready condition on Failed with its English detail in conditionArgs; once the
+// template exists the reason no longer carries arguments, so the entry goes.
+func TestGameServer_ConditionArgsSetAndCleared(t *testing.T) {
+	ns := newNamespace(t)
+	startMgr(t, ns, withGameServerReconciler(t, ns))
+	tmpl := buildGameTemplate(uniqueName("late-template"))
+	gs := buildGameServer(ns, "args-waiting", tmpl.Name)
+	if err := k8sClient.Create(t.Context(), gs); err != nil {
+		t.Fatal(err)
+	}
+	key := types.NamespacedName{Namespace: ns, Name: gs.Name}
+	wantDetail := fmt.Sprintf("GameTemplate %q not found", tmpl.Name)
+	eventually(t, func() (bool, string) {
+		if err := k8sClient.Get(t.Context(), key, gs); err != nil {
+			return false, err.Error()
+		}
+		ready := meta.FindStatusCondition(gs.Status.Conditions, "Ready")
+		if ready == nil || ready.Reason != "Failed" {
+			return false, "waiting for Ready reason Failed"
+		}
+		got := gs.Status.ConditionArgs["Ready"]["detail"]
+		return got == wantDetail, fmt.Sprintf("conditionArgs[Ready][detail] = %q, want %q", got, wantDetail)
+	})
+
+	if err := k8sClient.Create(t.Context(), tmpl); err != nil {
+		t.Fatal(err)
+	}
+	deleteCleanup(t, tmpl)
+	eventually(t, func() (bool, string) {
+		if err := k8sClient.Get(t.Context(), key, gs); err != nil {
+			return false, err.Error()
+		}
+		ready := meta.FindStatusCondition(gs.Status.Conditions, "Ready")
+		if ready == nil || ready.Reason == "Failed" {
+			return false, "waiting for Ready reason to leave Failed"
+		}
+		_, present := gs.Status.ConditionArgs["Ready"]
+		return !present, "conditionArgs[Ready] still present after recovery"
+	})
+}
+
+// TestGameServer_ConditionArgsAddressInUse: the second server requesting an
+// address held by the first reports AddressInUse with the address and the
+// holder's name as arguments.
+func TestGameServer_ConditionArgsAddressInUse(t *testing.T) {
+	ns := newNamespace(t)
+	startMgr(t, ns, withGameServerReconcilerAddressManager(t, ns, "metallb"))
+
+	tmpl := buildGameTemplate(uniqueName("minecraft"))
+	if err := k8sClient.Create(t.Context(), tmpl); err != nil {
+		t.Fatalf("create template: %v", err)
+	}
+	deleteCleanup(t, tmpl)
+
+	const addr = "203.0.113.20"
+	gs1 := buildGameServer(ns, "args-holder", tmpl.Name)
+	gs1.Spec.Networking.Expose = "LoadBalancer"
+	gs1.Spec.Networking.Address = addr
+	if err := k8sClient.Create(t.Context(), gs1); err != nil {
+		t.Fatalf("create server1: %v", err)
+	}
+	eventually(t, func() (bool, string) {
+		var svc corev1.Service
+		if err := k8sClient.Get(t.Context(),
+			types.NamespacedName{Namespace: ns, Name: "args-holder"}, &svc); err != nil {
+			return false, "service: " + err.Error()
+		}
+		return true, ""
+	})
+
+	// As in TestGameServer_AddressConflictDetection, no address manager runs in
+	// envtest, so the LoadBalancer ingress is written as a real address manager
+	// would write it.
+	if err := retry.RetryOnConflict(retry.DefaultBackoff, func() error {
+		var svc corev1.Service
+		if err := k8sClient.Get(t.Context(),
+			types.NamespacedName{Namespace: ns, Name: "args-holder"}, &svc); err != nil {
+			return err
+		}
+		svc.Status.LoadBalancer.Ingress = []corev1.LoadBalancerIngress{{IP: addr}}
+		return k8sClient.Status().Update(t.Context(), &svc)
+	}); err != nil {
+		t.Fatalf("update server1 service status: %v", err)
+	}
+	eventually(t, func() (bool, string) {
+		var gs gameplanev1alpha1.GameServer
+		if err := k8sClient.Get(t.Context(),
+			types.NamespacedName{Namespace: ns, Name: "args-holder"}, &gs); err != nil {
+			return false, "get server1: " + err.Error()
+		}
+		for _, ep := range gs.Status.Endpoints {
+			if ep.Host == addr {
+				return true, ""
+			}
+		}
+		return false, "server1 endpoints do not yet reflect " + addr
+	})
+
+	gs2 := buildGameServer(ns, "args-contender", tmpl.Name)
+	gs2.Spec.Networking.Expose = "LoadBalancer"
+	gs2.Spec.Networking.Address = addr
+	if err := k8sClient.Create(t.Context(), gs2); err != nil {
+		t.Fatalf("create server2: %v", err)
+	}
+	eventually(t, func() (bool, string) {
+		var gs gameplanev1alpha1.GameServer
+		if err := k8sClient.Get(t.Context(),
+			types.NamespacedName{Namespace: ns, Name: "args-contender"}, &gs); err != nil {
+			return false, "get server2: " + err.Error()
+		}
+		cond := meta.FindStatusCondition(gs.Status.Conditions, gameplanev1alpha1.GameServerConditionAddressAssignment)
+		if cond == nil {
+			return false, "AddressAssignment condition not found"
+		}
+		if cond.Reason != "AddressInUse" {
+			return false, "AddressAssignment reason = " + cond.Reason + ", want AddressInUse"
+		}
+		want := map[string]string{"address": addr, "server": "args-holder"}
+		got := gs.Status.ConditionArgs[gameplanev1alpha1.GameServerConditionAddressAssignment]
+		return reflect.DeepEqual(got, want), fmt.Sprintf("conditionArgs[AddressAssignment] = %v, want %v", got, want)
+	})
+}
+
+// TestGameServer_ConditionArgsInvalidAddress: a requested address that does
+// not parse reports InvalidAddress with the raw address as its argument.
+func TestGameServer_ConditionArgsInvalidAddress(t *testing.T) {
+	ns := newNamespace(t)
+	startMgr(t, ns, withGameServerReconcilerAddressManager(t, ns, "metallb"))
+
+	tmpl := buildGameTemplate(uniqueName("minecraft"))
+	if err := k8sClient.Create(t.Context(), tmpl); err != nil {
+		t.Fatalf("create template: %v", err)
+	}
+	deleteCleanup(t, tmpl)
+
+	gs := buildGameServer(ns, "args-bad-address", tmpl.Name)
+	gs.Spec.Networking.Expose = "LoadBalancer"
+	gs.Spec.Networking.Address = "not-an-ip"
+	if err := k8sClient.Create(t.Context(), gs); err != nil {
+		t.Fatalf("create server: %v", err)
+	}
+	eventually(t, func() (bool, string) {
+		var got gameplanev1alpha1.GameServer
+		if err := k8sClient.Get(t.Context(),
+			types.NamespacedName{Namespace: ns, Name: gs.Name}, &got); err != nil {
+			return false, "get server: " + err.Error()
+		}
+		cond := meta.FindStatusCondition(got.Status.Conditions, gameplanev1alpha1.GameServerConditionAddressAssignment)
+		if cond == nil {
+			return false, "AddressAssignment condition not found"
+		}
+		if cond.Reason != "InvalidAddress" {
+			return false, "AddressAssignment reason = " + cond.Reason + ", want InvalidAddress"
+		}
+		addr := got.Status.ConditionArgs[gameplanev1alpha1.GameServerConditionAddressAssignment]["address"]
+		return addr == "not-an-ip", fmt.Sprintf("conditionArgs address = %q, want not-an-ip", addr)
+	})
+}
diff --git a/operator/internal/controller/gameserver_controller.go b/operator/internal/controller/gameserver_controller.go
index 9025a1d31..f3c0ffaa5 100644
--- a/operator/internal/controller/gameserver_controller.go
+++ b/operator/internal/controller/gameserver_controller.go
@@ -2344,6 +2344,7 @@ func (r *GameServerReconciler) setPhase(
 		Message:            msg,
 		ObservedGeneration: gs.Generation,
 	})
+	setConditionArgs(&gs.Status, "Ready", map[string]string{"detail": msg})
 	return r.Status().Patch(ctx, gs, client.MergeFrom(base))
 }
 
diff --git a/operator/internal/controller/gameserver_status.go b/operator/internal/controller/gameserver_status.go
index f2a00b36f..54393de0b 100644
--- a/operator/internal/controller/gameserver_status.go
+++ b/operator/internal/controller/gameserver_status.go
@@ -88,7 +88,7 @@ func (r *GameServerReconciler) reconcileStatus(
 	var prov *provisioningInfo
 	if phase == gameplanev1alpha1.GameServerPhasePending || phase == gameplanev1alpha1.GameServerPhaseStarting {
 		pvcName := gs.Name + "-data"
-		if _, pvcMsg, provisioning, err := checkPVCProvisioningFailure(ctx, r.Client, gs.Namespace, pvcName); err != nil {
+		if scName, pvcMsg, provisioning, err := checkPVCProvisioningFailure(ctx, r.Client, gs.Namespace, pvcName); err != nil {
 			// Non-NotFound error checking the PVC or StorageClass; surface it.
 			return 0, fmt.Errorf("check PVC provisioning: %w", err)
 		} else if provisioning {
@@ -98,6 +98,7 @@ func (r *GameServerReconciler) reconcileStatus(
 			prov = &provisioningInfo{
 				reason:  GameServerConditionReasonPVCProvisioningFailed,
 				message: fmt.Sprintf("PVC %q: %s", pvcName, pvcMsg),
+				args:    map[string]string{"pvc": pvcName, "storageClass": scName},
 			}
 		}
 	}
@@ -123,10 +124,10 @@ func (r *GameServerReconciler) reconcileStatus(
 				// derivePhase re-evaluates every reconcile, so a later
 				// recovery returns the phase to Running.
 				phase = gameplanev1alpha1.GameServerPhaseFailed
-				prov = &provisioningInfo{reason: fr, message: fm}
+				prov = &provisioningInfo{reason: fr, message: fm, args: provisioningArgs(&pod, fr)}
 			} else {
 				reason, message := provisioningReason(&pod, heartbeatFresh(gs))
-				prov = &provisioningInfo{reason: reason, message: message}
+				prov = &provisioningInfo{reason: reason, message: message, args: provisioningArgs(&pod, reason)}
 			}
 		}
 	}
@@ -195,10 +196,12 @@ func (r *GameServerReconciler) reconcileStatus(
 	gs.Status.Conditions = computeTunnelConditions(gs, tunnelPlan, tunnelDep)
 
 	// Validate and merge playit tunnel endpoints if present.
+	var playitErr string
 	if gs.Spec.Networking.Tunnel != nil && gs.Spec.Networking.Tunnel.Provider == "playit" &&
 		len(gs.Status.TunnelEndpoints) > 0 {
 		advertisedPorts := getAdvertisedPortNames(tmpl)
 		validEndpoints, errMsg := validatePlayitEndpoints(gs.Status.TunnelEndpoints, advertisedPorts)
+		playitErr = errMsg
 		if errMsg != "" {
 			// Set condition on validation failure; invalid entries are discarded
 			invalidCond := metav1.Condition{
@@ -278,6 +281,20 @@ func (r *GameServerReconciler) reconcileStatus(
 		gs.Status.StartedAt = nil
 	}
 
+	// Recomputed from the final conditions so the args follow each condition
+	// and are dropped when its reason has none. Out-of-band writers
+	// (setPhase, setTunnelCredentialRefused, clearTunnelCredentialRefused)
+	// maintain their own entries; see gameserver_condition_args.go.
+	gs.Status.ConditionArgs = deriveConditionArgs(gs, conditionArgsInput{
+		prov:         prov,
+		plan:         addrPlan,
+		assigned:     loadBalancerAddress(svcPtr),
+		conflicting:  conflictingServer,
+		tunnelPlan:   tunnelPlan,
+		playitErr:    playitErr,
+		idleSchedErr: idleScheduleErr,
+	})
+
 	if !reflect.DeepEqual(orig, &gs.Status) {
 		if err := r.Status().Patch(ctx, gs, client.MergeFrom(base)); err != nil {
 			return 0, err
@@ -851,6 +868,9 @@ const gameContainerName = "game"
 type provisioningInfo struct {
 	reason  string
 	message string
+	// args are the values the localized text of reason needs; see
+	// provisioningArgs. nil when the reason has none.
+	args map[string]string
 }
 
 // provisioningReason inspects a Starting pod's container states to explain
@@ -1052,19 +1072,7 @@ func computeTunnelConditions(
 	// TunnelHostnameIgnored always reflects the current spec rather than going
 	// stale behind an early return (e.g. a hostname cleared while the tunnel
 	// Deployment isn't ready yet, or the provider config is invalid) — F-055.
-	var ignoredSettings []string
-	if gs.Spec.Networking.Hostname != "" {
-		ignoredSettings = append(ignoredSettings, "hostname")
-	}
-	if len(gs.Spec.Networking.SourceRanges) > 0 {
-		ignoredSettings = append(ignoredSettings, "sourceRanges")
-	}
-	for _, po := range gs.Spec.Networking.PortOverrides {
-		if po.NodePort != 0 {
-			ignoredSettings = append(ignoredSettings, "nodePort")
-			break
-		}
-	}
+	ignoredSettings := ignoredTunnelSettings(gs)
 	if len(ignoredSettings) > 0 {
 		conds = upsertCondition(conds, metav1.Condition{
 			Type:               "TunnelHostnameIgnored",
diff --git a/operator/internal/controller/gameserver_tunnel.go b/operator/internal/controller/gameserver_tunnel.go
index db8f3af3e..a950292b2 100644
--- a/operator/internal/controller/gameserver_tunnel.go
+++ b/operator/internal/controller/gameserver_tunnel.go
@@ -452,6 +452,11 @@ func (r *GameServerReconciler) setTunnelCredentialRefused(ctx context.Context, g
 		Message:            fmt.Sprintf("tunnel credentials secret %q is not owned by this GameServer (no ownerReference matching its name and UID); %s", secretName, remedy),
 		ObservedGeneration: gs.Generation,
 	})
+	remedyKind := "other"
+	if secretName == gs.Name+"-tunnel-auth" {
+		remedyKind = "defaultName"
+	}
+	setConditionArgs(&gs.Status, "TunnelReady", map[string]string{"secret": secretName, "remedy": remedyKind})
 	if err := r.Status().Patch(ctx, gs, client.MergeFrom(base)); err != nil {
 		return fmt.Errorf("patch TunnelReady condition for %s/%s: %w", gs.Namespace, gs.Name, err)
 	}
@@ -469,6 +474,7 @@ func (r *GameServerReconciler) clearTunnelCredentialRefused(ctx context.Context,
 	}
 	base := gs.DeepCopy()
 	gs.Status.Conditions = removeCondition(gs.Status.Conditions, "TunnelReady")
+	setConditionArgs(&gs.Status, "TunnelReady", nil)
 	// A GameServer that no longer exists has no status left to clear.
 	if err := r.Status().Patch(ctx, gs, client.MergeFrom(base)); err != nil && !apierrors.IsNotFound(err) {
 		return fmt.Errorf("clear TunnelCredentialRefused condition for %s/%s: %w", gs.Namespace, gs.Name, err)
diff --git a/operator/internal/controller/module_controller.go b/operator/internal/controller/module_controller.go
index f5aeaa38d..c3c54b48a 100644
--- a/operator/internal/controller/module_controller.go
+++ b/operator/internal/controller/module_controller.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"slices"
 	"strings"
+	"time"
 
 	"golang.org/x/mod/semver"
 	"k8s.io/apimachinery/pkg/api/equality"
@@ -18,6 +19,7 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/handler"
 	"sigs.k8s.io/controller-runtime/pkg/log"
 	"sigs.k8s.io/controller-runtime/pkg/reconcile"
+	"sigs.k8s.io/controller-runtime/pkg/recorder"
 	"sigs.k8s.io/yaml"
 
 	gameplanev1alpha1 "github.com/GameplanePanel/gameplane/operator/api/v1alpha1"
@@ -58,6 +60,10 @@ type ModuleReconciler struct {
 	// NewVerifier is overridden in tests with an in-process fake. nil →
 	// the real cosign verifier from verify.Build.
 	NewVerifier func(ctx context.Context, src *gameplanev1alpha1.ModuleSource) (verify.Verifier, error)
+
+	// EventRecorder surfaces module translation problems as Warning events
+	// on the GameTemplate. nil disables events (unit tests).
+	EventRecorder recorder.EventRecorder
 }
 
 // +kubebuilder:rbac:groups=gameplane.local,resources=modules,verbs=get;list;watch;update;patch
@@ -65,6 +71,7 @@ type ModuleReconciler struct {
 // +kubebuilder:rbac:groups=gameplane.local,resources=modules/finalizers,verbs=update
 // +kubebuilder:rbac:groups=gameplane.local,resources=gametemplates,verbs=get;list;watch;create;update;patch;delete
 // +kubebuilder:rbac:groups=gameplane.local,resources=gameservers,verbs=get;list;watch
+// +kubebuilder:rbac:groups="",resources=configmaps,verbs=get;list;watch;create;update;patch;delete
 
 func (r *ModuleReconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
 	return requeueOnConflict(r.reconcile(ctx, req))
@@ -191,9 +198,17 @@ func (r *ModuleReconciler) reconcile(ctx context.Context, req ctrl.Request) (ctr
 	}
 
 	// Materialize a GameTemplate.
-	if err := r.applyTemplate(ctx, &mod, bundle, desiredVersion, src.Name); err != nil {
+	tmpl, err := r.applyTemplate(ctx, &mod, bundle, desiredVersion, src.Name)
+	if err != nil {
 		return r.markFailed(ctx, &mod, "ApplyTemplate", err)
 	}
+	// Translation problems never fail the install (FR-034). A failed
+	// ConfigMap write is retried a minute later.
+	var localesRetry time.Duration
+	if err := r.applyLocales(ctx, tmpl, bundle); err != nil {
+		log.FromContext(ctx).Error(err, "module translations not stored; will retry", "module", mod.Name)
+		localesRetry = retryLocalesAfter
+	}
 
 	// Update Status to Ready. Record the version being replaced as the
 	// rollback target before overwriting it (only when it actually changes).
@@ -236,13 +251,13 @@ func (r *ModuleReconciler) reconcile(ctx context.Context, req ctrl.Request) (ctr
 	if err := r.Status().Update(ctx, &mod); err != nil {
 		return ctrl.Result{}, err
 	}
-	return ctrl.Result{}, nil
+	return ctrl.Result{RequeueAfter: localesRetry}, nil
 }
 
-func (r *ModuleReconciler) applyTemplate(ctx context.Context, mod *gameplanev1alpha1.Module, bundle *modsrc.Bundle, version, sourceName string) error {
+func (r *ModuleReconciler) applyTemplate(ctx context.Context, mod *gameplanev1alpha1.Module, bundle *modsrc.Bundle, version, sourceName string) (*gameplanev1alpha1.GameTemplate, error) {
 	parsed := &gameplanev1alpha1.GameTemplate{}
 	if err := yaml.Unmarshal(bundle.TemplateYAML, parsed); err != nil {
-		return fmt.Errorf("parse template.yaml: %w", err)
+		return nil, fmt.Errorf("parse template.yaml: %w", err)
 	}
 
 	// Legacy bundles declare a singular spec.category; the typed GameTemplate
@@ -279,7 +294,7 @@ func (r *ModuleReconciler) applyTemplate(ctx context.Context, mod *gameplanev1al
 
 	// Set the OwnerReference so deleting the Module GCs the template.
 	if err := controllerutil.SetControllerReference(mod, desired, r.Scheme); err != nil {
-		return fmt.Errorf("set owner ref: %w", err)
+		return nil, fmt.Errorf("set owner ref: %w", err)
 	}
 
 	// Server-side apply or create-or-update via SSA-like pattern. We do
@@ -288,24 +303,30 @@ func (r *ModuleReconciler) applyTemplate(ctx context.Context, mod *gameplanev1al
 	var existing gameplanev1alpha1.GameTemplate
 	err := r.Get(ctx, types.NamespacedName{Name: desired.Name}, &existing)
 	if apierrors.IsNotFound(err) {
-		return r.Create(ctx, desired)
+		if err := r.Create(ctx, desired); err != nil {
+			return nil, err
+		}
+		return desired, nil
 	}
 	if err != nil {
-		return err
+		return nil, err
 	}
 	// Verify ownership before clobbering — refuse to mutate a template
 	// that wasn't created by this Module (e.g. pre-existing manual
 	// install with the same name).
 	if existing.Labels[gameplanev1alpha1.LabelManagedBy] != gameplanev1alpha1.ManagedByModule {
-		return fmt.Errorf("template %q exists and is not module-managed", desired.Name)
+		return nil, fmt.Errorf("template %q exists and is not module-managed", desired.Name)
 	}
 	if !ownedBy(&existing, mod) {
-		return fmt.Errorf("template %q is owned by a different Module", desired.Name)
+		return nil, fmt.Errorf("template %q is owned by a different Module", desired.Name)
 	}
 	existing.Spec = desired.Spec
 	existing.Labels = desired.Labels
 	existing.Annotations = mergeAnnotations(existing.Annotations, desired.Annotations)
-	return r.Update(ctx, &existing)
+	if err := r.Update(ctx, &existing); err != nil {
+		return nil, err
+	}
+	return &existing, nil
 }
 
 // finalize handles the deletion path. We refuse to release the
diff --git a/operator/internal/controller/module_locales.go b/operator/internal/controller/module_locales.go
new file mode 100644
index 000000000..5c2f39eaf
--- /dev/null
+++ b/operator/internal/controller/module_locales.go
@@ -0,0 +1,502 @@
+package controller
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"sort"
+	"strings"
+	"time"
+	"unicode/utf8"
+
+	corev1 "k8s.io/api/core/v1"
+	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/api/meta"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/types"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/controller/controllerutil"
+	"sigs.k8s.io/controller-runtime/pkg/log"
+	"sigs.k8s.io/yaml"
+
+	"github.com/GameplanePanel/gameplane/i18n/modlocale"
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+	gameplanev1alpha1 "github.com/GameplanePanel/gameplane/operator/api/v1alpha1"
+	"github.com/GameplanePanel/gameplane/operator/internal/modsrc"
+	"github.com/GameplanePanel/gameplane/operator/internal/oci"
+)
+
+const (
+	// localesConfigMapSuffix names the ConfigMap that holds a module's
+	// validated translations: <GameTemplate name> + this suffix.
+	localesConfigMapSuffix = "-locales"
+	// localesMaxBytes bounds the ConfigMap data (a ConfigMap is capped at
+	// 1 MiB; this leaves headroom for metadata).
+	localesMaxBytes = 900 * 1024
+	// maxLocaleProblems caps the per-entry lines in one Warning event.
+	maxLocaleProblems = 20
+	// defaultLocalesNamespace is used when the reconciler has no namespace.
+	defaultLocalesNamespace = "gameplane-system"
+
+	// localesProblemsAnnotation records a fingerprint of the problem list last
+	// reported on a GameTemplate, so a re-pull of the same bundle does not
+	// repeat the Warning events. It is removed when the list is empty.
+	localesProblemsAnnotation = "gameplane.local/locales-problems"
+
+	eventReasonInvalidLocaleEntries = "InvalidLocaleEntries"
+	eventReasonLocalesTooLarge      = "LocalesTooLarge"
+	eventReasonLocalesWriteFailed   = "LocalesWriteFailed"
+
+	// retryLocalesAfter is the requeue delay after a failed ConfigMap write.
+	retryLocalesAfter = time.Minute
+)
+
+// localeOutcome is the result of validating a module's translations.
+type localeOutcome struct {
+	// Data maps "<tag>.json" to the marshalled valid entries.
+	Data map[string]string
+	// Problems lists "tag:id: problem" lines, sorted by tag then id.
+	Problems []string
+	// PerLang counts the dropped entries of each tag.
+	PerLang map[string]int
+	// Rejected lists the tags whose whole file was rejected (bad tag or a
+	// malformed file).
+	Rejected []string
+	// Dropped lists the tags left out by the size bound.
+	Dropped []string
+	// Oversized lists the tags whose file was larger than
+	// oci.MaxLocaleLayerSize, or did not fit oci.MaxLocaleTotalSize, and was
+	// not read. They are never stored.
+	Oversized []string
+	// WriteErr is set when the translations ConfigMap could not be written
+	// or deleted, so nothing new is being served.
+	WriteErr error
+}
+
+// buildLocales validates every translation layer against the reference pack
+// derived from the module's template. Invalid entries are dropped, never
+// repaired; a file that does not parse is dropped whole. Languages are added
+// in tag order until the next one would exceed localesMaxBytes; that one and
+// every later one are left out.
+func buildLocales(ref map[string]pack.Entry, layers map[string][]byte) localeOutcome {
+	return buildLocalesWithOversized(ref, layers, nil)
+}
+
+// buildLocalesWithOversized is buildLocales plus the tags whose file was too
+// large to read; they are recorded on the outcome, never stored.
+func buildLocalesWithOversized(ref map[string]pack.Entry, layers map[string][]byte, oversized []string) localeOutcome {
+	out := localeOutcome{Data: map[string]string{}, PerLang: map[string]int{}}
+	// An oversized file was never read, but its name still comes from the
+	// bundle: a name that is not a language tag is rejected like any other.
+	for _, tag := range oversized {
+		if !pack.ValidTag(tag) {
+			out.Problems = append(out.Problems, fmt.Sprintf("%s:%s: invalid language tag", tag, pack.IDPack))
+			out.Rejected = append(out.Rejected, tag)
+			continue
+		}
+		out.Oversized = append(out.Oversized, tag)
+	}
+	sort.Strings(out.Oversized)
+	tags := make([]string, 0, len(layers))
+	for tag := range layers {
+		tags = append(tags, tag)
+	}
+	sort.Strings(tags)
+
+	used := 0
+	full := false
+	for _, tag := range tags {
+		file := tag + ".json"
+		if !pack.ValidTag(tag) {
+			out.Problems = append(out.Problems, fmt.Sprintf("%s:%s: invalid language tag", tag, pack.IDPack))
+			out.Rejected = append(out.Rejected, tag)
+			continue
+		}
+		tr, err := pack.ParseEntries(layers[tag])
+		if err != nil {
+			out.Problems = append(out.Problems, fmt.Sprintf("%s:%s: %v", tag, pack.IDPack, err))
+			out.Rejected = append(out.Rejected, tag)
+			continue
+		}
+		bad := map[string]struct{}{}
+		for _, f := range pack.ValidateTranslation(ref, tr, file) {
+			if f.Severity != pack.SeverityError {
+				continue
+			}
+			out.Problems = append(out.Problems, fmt.Sprintf("%s:%s: %s", tag, f.ID, f.Message))
+			bad[f.ID] = struct{}{}
+		}
+		if len(bad) > 0 {
+			out.PerLang[tag] = len(bad)
+		}
+		kept := pack.Valid(ref, tr)
+		for id := range bad {
+			delete(kept, id)
+		}
+		if len(kept) == 0 {
+			continue
+		}
+		if full {
+			out.Dropped = append(out.Dropped, tag)
+			continue
+		}
+		data, err := pack.Marshal(kept)
+		if err != nil {
+			out.Problems = append(out.Problems, fmt.Sprintf("%s:%s: %v", tag, pack.IDPack, err))
+			out.Rejected = append(out.Rejected, tag)
+			continue
+		}
+		if used+len(file)+len(data) > localesMaxBytes {
+			full = true
+			out.Dropped = append(out.Dropped, tag)
+			continue
+		}
+		used += len(file) + len(data)
+		out.Data[file] = string(data)
+	}
+	return out
+}
+
+// localesCondition turns an outcome into the LocalesValid condition. The
+// reason priority is WriteFailed (nothing new is served), LocalesTooLarge (whole
+// languages are missing), InvalidEntries, then Valid.
+func localesCondition(out localeOutcome) metav1.Condition {
+	cond := localesConditionUnclipped(out)
+	// Tags come from the bundle, so a hostile one could push the message past
+	// the API limit and make every status patch fail.
+	cond.Message = clipBytes(cond.Message, maxConditionMessageBytes)
+	return cond
+}
+
+// maxConditionMessageBytes is the metav1.Condition message length limit.
+const maxConditionMessageBytes = 32768
+
+func localesConditionUnclipped(out localeOutcome) metav1.Condition {
+	var parts []string
+	if len(out.Oversized) > 0 {
+		parts = append(parts, fmt.Sprintf("too large to read (over %d KiB per file or %d KiB for all languages together): %s", oci.MaxLocaleLayerSize/1024, oci.MaxLocaleTotalSize/1024, strings.Join(out.Oversized, ", ")))
+	}
+	if len(out.Dropped) > 0 {
+		parts = append(parts, "left out because of the size limit: "+strings.Join(out.Dropped, ", "))
+	}
+	langs := make([]string, 0, len(out.PerLang))
+	for tag := range out.PerLang {
+		langs = append(langs, tag)
+	}
+	sort.Strings(langs)
+	rejected := map[string]bool{}
+	for _, tag := range out.Rejected {
+		rejected[tag] = true
+	}
+	for _, tag := range langs {
+		if rejected[tag] {
+			continue
+		}
+		n := out.PerLang[tag]
+		noun := "entries"
+		if n == 1 {
+			noun = "entry"
+		}
+		parts = append(parts, fmt.Sprintf("%s: %d %s dropped", tag, n, noun))
+	}
+	for _, tag := range out.Rejected {
+		parts = append(parts, fmt.Sprintf("%s: file rejected", tag))
+	}
+	// The reasons are string literals: the condition-ids guard reads them from
+	// the composite literals below.
+	switch {
+	case out.WriteErr != nil:
+		parts = append([]string{"translations could not be stored: " + out.WriteErr.Error()}, parts...)
+		return metav1.Condition{
+			Type:    gameplanev1alpha1.GameTemplateConditionLocalesValid,
+			Status:  metav1.ConditionFalse,
+			Reason:  "WriteFailed",
+			Message: strings.Join(parts, "; "),
+		}
+	case len(out.Dropped) > 0 || len(out.Oversized) > 0:
+		return metav1.Condition{
+			Type:    gameplanev1alpha1.GameTemplateConditionLocalesValid,
+			Status:  metav1.ConditionFalse,
+			Reason:  "LocalesTooLarge",
+			Message: strings.Join(parts, "; "),
+		}
+	case len(parts) > 0:
+		return metav1.Condition{
+			Type:    gameplanev1alpha1.GameTemplateConditionLocalesValid,
+			Status:  metav1.ConditionFalse,
+			Reason:  "InvalidEntries",
+			Message: strings.Join(parts, "; "),
+		}
+	default:
+		return metav1.Condition{
+			Type:    gameplanev1alpha1.GameTemplateConditionLocalesValid,
+			Status:  metav1.ConditionTrue,
+			Reason:  "Valid",
+			Message: "All module translations are valid.",
+		}
+	}
+}
+
+// problemsFingerprint identifies the problem list of an outcome: the first 12
+// hex characters of a SHA-256 over its sorted lines. It is empty when there is
+// nothing to report.
+func problemsFingerprint(out localeOutcome) string {
+	var lines []string
+	lines = append(lines, out.Problems...)
+	for _, tag := range out.Dropped {
+		lines = append(lines, "dropped:"+tag)
+	}
+	for _, tag := range out.Oversized {
+		lines = append(lines, "oversized:"+tag)
+	}
+	if out.WriteErr != nil {
+		// The error text can vary between retries (timeouts, conflicts); a
+		// failed write counts as one problem so retries do not repeat events.
+		lines = append(lines, "write:failed")
+	}
+	if len(lines) == 0 {
+		return ""
+	}
+	sort.Strings(lines)
+	sum := sha256.Sum256([]byte(strings.Join(lines, "\n")))
+	return hex.EncodeToString(sum[:])[:12]
+}
+
+// tooLargeLanguages merges the oversized and dropped tags, sorted and unique.
+func tooLargeLanguages(out localeOutcome) []string {
+	seen := map[string]struct{}{}
+	var tags []string
+	for _, list := range [][]string{out.Oversized, out.Dropped} {
+		for _, tag := range list {
+			if _, dup := seen[tag]; dup {
+				continue
+			}
+			seen[tag] = struct{}{}
+			tags = append(tags, tag)
+		}
+	}
+	sort.Strings(tags)
+	return tags
+}
+
+// problemEventNote joins up to maxLocaleProblems problem lines for an event.
+func problemEventNote(problems []string) string {
+	// events.k8s.io/v1 rejects a note over 1024 bytes, so lines are also
+	// bounded by bytes: each line is clipped and the note stops early,
+	// keeping room for the "... and N more" trailer.
+	const maxLineBytes = 160
+	const trailerReserve = 32
+	var b strings.Builder
+	shown := 0
+	for _, line := range problems {
+		if shown == maxLocaleProblems {
+			break
+		}
+		line = clipBytes(line, maxLineBytes)
+		if b.Len()+len(line)+1 > maxEventNoteBytes-trailerReserve {
+			break
+		}
+		if shown > 0 {
+			b.WriteByte('\n')
+		}
+		b.WriteString(line)
+		shown++
+	}
+	if rest := len(problems) - shown; rest > 0 {
+		if shown > 0 {
+			b.WriteByte('\n')
+		}
+		fmt.Fprintf(&b, "... and %d more", rest)
+	}
+	return b.String()
+}
+
+// maxEventNoteBytes is the events.k8s.io/v1 note length limit.
+const maxEventNoteBytes = 1024
+
+// clipBytes shortens s to at most n bytes without splitting a UTF-8 rune.
+func clipBytes(s string, n int) string {
+	if len(s) <= n {
+		return s
+	}
+	cut := n - len("...")
+	for cut > 0 && !utf8.RuneStart(s[cut]) {
+		cut--
+	}
+	return s[:cut] + "..."
+}
+
+// localesReference derives the English reference pack of a bundle.
+func localesReference(b *modsrc.Bundle) (map[string]pack.Entry, error) {
+	var tmpl map[string]any
+	if err := yaml.Unmarshal(b.TemplateYAML, &tmpl); err != nil {
+		return nil, fmt.Errorf("parse template.yaml: %w", err)
+	}
+	module := map[string]any{
+		"displayName": b.Metadata.DisplayName,
+		"summary":     b.Metadata.Summary,
+	}
+	return modlocale.References(modlocale.Derive(module, tmpl)), nil
+}
+
+func (r *ModuleReconciler) localesNamespace() string {
+	if r.Namespace != "" {
+		return r.Namespace
+	}
+	return defaultLocalesNamespace
+}
+
+// applyLocales validates the bundle's translation layers and publishes the
+// valid entries in the "<template>-locales" ConfigMap, owned by the
+// GameTemplate, in the operator namespace. It reports problems through the
+// template's LocalesValid condition and Warning events, which fire only when
+// the problem list changes. A translation problem never fails a module
+// install; the only error returned is a failed ConfigMap write or delete, so
+// the caller can retry later.
+func (r *ModuleReconciler) applyLocales(ctx context.Context, tmpl *gameplanev1alpha1.GameTemplate, b *modsrc.Bundle) error {
+	if tmpl == nil || b == nil {
+		return nil
+	}
+	logger := log.FromContext(ctx).WithValues("template", tmpl.Name)
+	key := types.NamespacedName{Namespace: r.localesNamespace(), Name: tmpl.Name + localesConfigMapSuffix}
+
+	if len(b.Locales) == 0 && len(b.OversizedLocales) == 0 {
+		if err := r.deleteLocalesConfigMap(ctx, key); err != nil {
+			// Stale translations are still served: report WriteFailed
+			// instead of clearing the condition.
+			logger.Error(err, "unable to remove stale module translations")
+			return r.reportLocales(ctx, tmpl, localeOutcome{WriteErr: err})
+		}
+		if err := r.setLocalesCondition(ctx, tmpl, nil); err != nil {
+			logger.Error(err, "unable to clear the LocalesValid condition")
+		}
+		if _, err := r.setLocalesFingerprint(ctx, tmpl, ""); err != nil {
+			logger.Error(err, "unable to clear the locales problems fingerprint")
+		}
+		return nil
+	}
+
+	ref, err := localesReference(b)
+	if err != nil {
+		logger.Error(err, "unable to derive module translation ids")
+		return nil
+	}
+	out := buildLocalesWithOversized(ref, b.Locales, b.OversizedLocales)
+
+	if len(out.Data) == 0 {
+		err = r.deleteLocalesConfigMap(ctx, key)
+	} else {
+		err = r.writeLocalesConfigMap(ctx, tmpl, key, out.Data)
+	}
+	if err != nil {
+		logger.Error(err, "unable to publish module translations")
+		out.WriteErr = err
+	}
+	return r.reportLocales(ctx, tmpl, out)
+}
+
+// reportLocales records out on the template's LocalesValid condition and, when
+// the problem list changed, emits the Warning events. It returns out.WriteErr.
+func (r *ModuleReconciler) reportLocales(ctx context.Context, tmpl *gameplanev1alpha1.GameTemplate, out localeOutcome) error {
+	logger := log.FromContext(ctx).WithValues("template", tmpl.Name)
+	cond := localesCondition(out)
+	cond.ObservedGeneration = tmpl.Generation
+	if err := r.setLocalesCondition(ctx, tmpl, &cond); err != nil {
+		logger.Error(err, "unable to record the LocalesValid condition")
+	}
+	changed, err := r.setLocalesFingerprint(ctx, tmpl, problemsFingerprint(out))
+	if err != nil {
+		// Without a stored fingerprint every re-pull would look new, so stay quiet.
+		logger.Error(err, "unable to record the locales problems fingerprint")
+		return out.WriteErr
+	}
+	if !changed {
+		return out.WriteErr
+	}
+	if len(out.Problems) > 0 {
+		r.recordLocaleEvent(tmpl, corev1.EventTypeWarning, eventReasonInvalidLocaleEntries, problemEventNote(out.Problems))
+	}
+	if tags := tooLargeLanguages(out); len(tags) > 0 {
+		r.recordLocaleEvent(tmpl, corev1.EventTypeWarning, eventReasonLocalesTooLarge,
+			clipBytes("translations too large or left out because of the size limit: "+strings.Join(tags, ", "), maxEventNoteBytes))
+	}
+	if out.WriteErr != nil {
+		r.recordLocaleEvent(tmpl, corev1.EventTypeWarning, eventReasonLocalesWriteFailed,
+			clipBytes("translations could not be stored: "+out.WriteErr.Error(), maxEventNoteBytes))
+	}
+	return out.WriteErr
+}
+
+// setLocalesFingerprint stores fp in the template's problems annotation (or
+// removes the annotation when fp is empty). It reports whether the stored
+// value changed, which is when the problem list changed and events are due.
+func (r *ModuleReconciler) setLocalesFingerprint(ctx context.Context, tmpl *gameplanev1alpha1.GameTemplate, fp string) (bool, error) {
+	prev := tmpl.Annotations[localesProblemsAnnotation]
+	if prev == fp {
+		return false, nil
+	}
+	base := tmpl.DeepCopy()
+	if fp == "" {
+		delete(tmpl.Annotations, localesProblemsAnnotation)
+	} else {
+		if tmpl.Annotations == nil {
+			tmpl.Annotations = map[string]string{}
+		}
+		tmpl.Annotations[localesProblemsAnnotation] = fp
+	}
+	if err := r.Patch(ctx, tmpl, client.MergeFrom(base)); err != nil {
+		return false, fmt.Errorf("patch GameTemplate %s annotations: %w", tmpl.Name, err)
+	}
+	return fp != "", nil
+}
+
+func (r *ModuleReconciler) writeLocalesConfigMap(ctx context.Context, tmpl *gameplanev1alpha1.GameTemplate, key types.NamespacedName, data map[string]string) error {
+	cm := &corev1.ConfigMap{ObjectMeta: metav1.ObjectMeta{Name: key.Name, Namespace: key.Namespace}}
+	_, err := controllerutil.CreateOrUpdate(ctx, r.Client, cm, func() error {
+		cm.Data = data
+		return controllerutil.SetControllerReference(tmpl, cm, r.Scheme)
+	})
+	if err != nil {
+		return fmt.Errorf("write ConfigMap %s: %w", key, err)
+	}
+	return nil
+}
+
+func (r *ModuleReconciler) deleteLocalesConfigMap(ctx context.Context, key types.NamespacedName) error {
+	cm := &corev1.ConfigMap{ObjectMeta: metav1.ObjectMeta{Name: key.Name, Namespace: key.Namespace}}
+	if err := r.Delete(ctx, cm); err != nil && !apierrors.IsNotFound(err) {
+		return fmt.Errorf("delete ConfigMap %s: %w", key, err)
+	}
+	return nil
+}
+
+// setLocalesCondition records cond on the template's status, or removes the
+// condition when cond is nil. It patches only when something changes.
+func (r *ModuleReconciler) setLocalesCondition(ctx context.Context, tmpl *gameplanev1alpha1.GameTemplate, cond *metav1.Condition) error {
+	base := tmpl.DeepCopy()
+	if cond == nil {
+		if meta.FindStatusCondition(tmpl.Status.Conditions, gameplanev1alpha1.GameTemplateConditionLocalesValid) == nil {
+			return nil
+		}
+		meta.RemoveStatusCondition(&tmpl.Status.Conditions, gameplanev1alpha1.GameTemplateConditionLocalesValid)
+	} else {
+		tmpl.Status.Conditions = upsertCondition(tmpl.Status.Conditions, *cond)
+		if sameConditions(base.Status.Conditions, tmpl.Status.Conditions) {
+			return nil
+		}
+	}
+	if err := r.Status().Patch(ctx, tmpl, client.MergeFrom(base)); err != nil {
+		return fmt.Errorf("patch GameTemplate %s status: %w", tmpl.Name, err)
+	}
+	return nil
+}
+
+// recordLocaleEvent emits an event on the template when an EventRecorder is
+// configured; it is a no-op otherwise.
+func (r *ModuleReconciler) recordLocaleEvent(tmpl *gameplanev1alpha1.GameTemplate, eventType, reason, note string) {
+	if r.EventRecorder == nil {
+		return
+	}
+	r.EventRecorder.Eventf(tmpl, nil, eventType, reason, reason, "%s", note)
+}
diff --git a/operator/internal/controller/module_locales_envtest_test.go b/operator/internal/controller/module_locales_envtest_test.go
new file mode 100644
index 000000000..54a6146c6
--- /dev/null
+++ b/operator/internal/controller/module_locales_envtest_test.go
@@ -0,0 +1,213 @@
+//go:build envtest
+
+package controller
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"testing"
+	"time"
+
+	corev1 "k8s.io/api/core/v1"
+	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/api/meta"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/client-go/tools/events"
+	"sigs.k8s.io/controller-runtime/pkg/manager"
+
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+	gameplanev1alpha1 "github.com/GameplanePanel/gameplane/operator/api/v1alpha1"
+	"github.com/GameplanePanel/gameplane/operator/internal/oci"
+)
+
+// withModuleReconcilerRecorder is withModuleReconciler with an event recorder
+// and an explicit namespace for the translation ConfigMap.
+func withModuleReconcilerRecorder(fake *fakeOCI, ns string, rec *events.FakeRecorder) setupReconciler {
+	return func(mgr manager.Manager) error {
+		return (&ModuleReconciler{
+			Client:        mgr.GetClient(),
+			Scheme:        mgr.GetScheme(),
+			Namespace:     ns,
+			NewFetcher:    fakeOCIFetcher(fake),
+			EventRecorder: rec,
+		}).SetupWithManager(mgr)
+	}
+}
+
+// installLocaleModule publishes a bundle with the given extra files, creates
+// the source and the Module, and returns the Module name.
+func installLocaleModule(t *testing.T, fake *fakeOCI, extra map[string][]byte) string {
+	t.Helper()
+	const ref = "local/test/minecraft-java"
+	bundle := fixtureBundle("minecraft-java", "1.0.0", "Minecraft (Java)")
+	for name, data := range extra {
+		bundle.files[name] = data
+	}
+	fake.putBundle(ref, "1.0.0", bundle)
+
+	srcName := uniqueName("modsrc")
+	createIndexedSource(t, srcName, "local/test", fake, []gameplanev1alpha1.ModuleEntry{{
+		Name:          "minecraft-java",
+		Reference:     ref,
+		Versions:      []string{"1.0.0"},
+		LatestVersion: "1.0.0",
+	}})
+	modName := uniqueName("mod")
+	mod := &gameplanev1alpha1.Module{
+		ObjectMeta: metav1.ObjectMeta{Name: modName},
+		Spec: gameplanev1alpha1.ModuleSpec{
+			Source: corev1.LocalObjectReference{Name: srcName},
+			Name:   "minecraft-java",
+		},
+	}
+	if err := k8sClient.Create(context.Background(), mod); err != nil {
+		t.Fatalf("create module: %v", err)
+	}
+	deleteCleanup(t, mod)
+	eventually(t, func() (bool, string) {
+		got := getModule(t, modName)
+		return got.Status.Phase == gameplanev1alpha1.ModulePhaseReady, "phase=" + got.Status.Phase + " err=" + got.Status.LastError
+	})
+	return modName
+}
+
+func localesConfigMap(ns, modName string) (*corev1.ConfigMap, error) {
+	cm := &corev1.ConfigMap{}
+	err := k8sClient.Get(context.Background(), types.NamespacedName{Namespace: ns, Name: modName + "-locales"}, cm)
+	return cm, err
+}
+
+func templateLocalesCondition(t *testing.T, modName string) *metav1.Condition {
+	t.Helper()
+	tmpl := getTemplateByName(t, modName)
+	return meta.FindStatusCondition(tmpl.Status.Conditions, gameplanev1alpha1.GameTemplateConditionLocalesValid)
+}
+
+// TestModule_PublishesValidLocalesAndReportsInvalidOnes covers a bundle with a
+// French layer holding one valid and one invalid entry.
+func TestModule_PublishesValidLocalesAndReportsInvalidOnes(t *testing.T) {
+	ns := newNamespace(t)
+	fake := newFakeOCI()
+	rec := events.NewFakeRecorder(32)
+	startMgr(t, ns, withModuleReconcilerRecorder(fake, ns, rec))
+
+	modName := installLocaleModule(t, fake, map[string][]byte{
+		"locales/fr.json": []byte(`{
+			"template.displayName": {"defaultMessage": "Minecraft (Java FR)"},
+			"module.displayName": {"defaultMessage": "{extra}"}
+		}`),
+	})
+
+	var cm *corev1.ConfigMap
+	eventually(t, func() (bool, string) {
+		var err error
+		cm, err = localesConfigMap(ns, modName)
+		return err == nil, fmt.Sprint(err)
+	})
+	entries, err := pack.ParseEntries([]byte(cm.Data["fr.json"]))
+	if err != nil {
+		t.Fatalf("parse fr.json: %v", err)
+	}
+	if len(entries) != 1 || entries["template.displayName"].DefaultMessage != "Minecraft (Java FR)" {
+		t.Errorf("fr.json entries = %v; want only the valid one", entries)
+	}
+
+	tmpl := getTemplateByName(t, modName)
+	if len(cm.OwnerReferences) != 1 || cm.OwnerReferences[0].UID != tmpl.UID {
+		t.Errorf("ownerReferences = %+v; want the GameTemplate %s", cm.OwnerReferences, tmpl.UID)
+	}
+
+	eventually(t, func() (bool, string) {
+		c := templateLocalesCondition(t, modName)
+		if c == nil {
+			return false, "no LocalesValid condition"
+		}
+		return c.Status == metav1.ConditionFalse && c.Reason == "InvalidEntries", fmt.Sprintf("%+v", c)
+	})
+
+	select {
+	case ev := <-rec.Events:
+		if !strings.Contains(ev, "Warning") || !strings.Contains(ev, "fr:") {
+			t.Errorf("event = %q", ev)
+		}
+	case <-time.After(5 * time.Second):
+		t.Fatal("no Warning event recorded")
+	}
+}
+
+// TestModule_LocalesOverSizeBoundAreLeftOutInTagOrder checks the 900 KiB bound.
+func TestModule_LocalesOverSizeBoundAreLeftOutInTagOrder(t *testing.T) {
+	ns := newNamespace(t)
+	fake := newFakeOCI()
+	startMgr(t, ns, withModuleReconcilerRecorder(fake, ns, events.NewFakeRecorder(32)))
+
+	layer := []byte(fmt.Sprintf(`{"template.displayName":{"defaultMessage":%q}}`, strings.Repeat("x", 500*1024)))
+	modName := installLocaleModule(t, fake, map[string][]byte{
+		"locales/de.json": layer,
+		"locales/fr.json": layer,
+	})
+
+	eventually(t, func() (bool, string) {
+		c := templateLocalesCondition(t, modName)
+		if c == nil {
+			return false, "no LocalesValid condition"
+		}
+		return c.Reason == "LocalesTooLarge", fmt.Sprintf("%+v", c)
+	})
+	cm, err := localesConfigMap(ns, modName)
+	if err != nil {
+		t.Fatalf("ConfigMap: %v", err)
+	}
+	if _, ok := cm.Data["de.json"]; !ok || len(cm.Data) != 1 {
+		t.Errorf("ConfigMap keys = %d; want only de.json", len(cm.Data))
+	}
+}
+
+// TestModule_WithoutLocalesHasNoConfigMap checks a bundle with no locale
+// layers: the Module is Ready and nothing is written.
+func TestModule_WithoutLocalesHasNoConfigMap(t *testing.T) {
+	ns := newNamespace(t)
+	fake := newFakeOCI()
+	startMgr(t, ns, withModuleReconcilerRecorder(fake, ns, events.NewFakeRecorder(8)))
+
+	modName := installLocaleModule(t, fake, nil)
+
+	if _, err := localesConfigMap(ns, modName); !apierrors.IsNotFound(err) {
+		t.Errorf("ConfigMap err = %v; want NotFound", err)
+	}
+	if c := templateLocalesCondition(t, modName); c != nil {
+		t.Errorf("unexpected LocalesValid condition %+v", c)
+	}
+}
+
+// TestModule_OversizedLocaleIsReportedByTag checks that a locale layer over the
+// per-file cap reaches the reconciler as an oversized tag and shows up as
+// LocalesTooLarge naming the language.
+func TestModule_OversizedLocaleIsReportedByTag(t *testing.T) {
+	ns := newNamespace(t)
+	fake := newFakeOCI()
+	rec := events.NewFakeRecorder(32)
+	startMgr(t, ns, withModuleReconcilerRecorder(fake, ns, rec))
+
+	modName := installLocaleModule(t, fake, map[string][]byte{
+		"locales/de.json": oci.OversizedLocale,
+	})
+
+	eventually(t, func() (bool, string) {
+		c := templateLocalesCondition(t, modName)
+		if c == nil {
+			return false, "no LocalesValid condition"
+		}
+		return c.Status == metav1.ConditionFalse && c.Reason == "LocalesTooLarge" && strings.Contains(c.Message, "de"), fmt.Sprintf("%+v", c)
+	})
+	select {
+	case ev := <-rec.Events:
+		if !strings.Contains(ev, "Warning") || !strings.Contains(ev, "de") {
+			t.Errorf("event = %q", ev)
+		}
+	case <-time.After(5 * time.Second):
+		t.Fatal("no Warning event recorded")
+	}
+}
diff --git a/operator/internal/controller/module_locales_review_test.go b/operator/internal/controller/module_locales_review_test.go
new file mode 100644
index 000000000..1c71f8514
--- /dev/null
+++ b/operator/internal/controller/module_locales_review_test.go
@@ -0,0 +1,77 @@
+package controller
+
+import (
+	"context"
+	"errors"
+	"strings"
+	"testing"
+
+	corev1 "k8s.io/api/core/v1"
+	"k8s.io/apimachinery/pkg/api/meta"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/client-go/tools/events"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/client/fake"
+	"sigs.k8s.io/controller-runtime/pkg/client/interceptor"
+
+	gameplanev1alpha1 "github.com/GameplanePanel/gameplane/operator/api/v1alpha1"
+)
+
+func TestApplyLocales_StaleDeleteFailureIsWriteFailed(t *testing.T) {
+	rec := events.NewFakeRecorder(8)
+	tmpl := &gameplanev1alpha1.GameTemplate{ObjectMeta: metav1.ObjectMeta{Name: "demo", UID: "tmpl-uid", Generation: 2}}
+	boom := errors.New("boom")
+	cl := fake.NewClientBuilder().WithScheme(scrapeScheme(t)).
+		WithObjects(tmpl).
+		WithStatusSubresource(&gameplanev1alpha1.GameTemplate{}).
+		WithInterceptorFuncs(interceptor.Funcs{
+			Delete: func(ctx context.Context, c client.WithWatch, obj client.Object, opts ...client.DeleteOption) error {
+				if _, ok := obj.(*corev1.ConfigMap); ok {
+					return boom
+				}
+				return c.Delete(ctx, obj, opts...)
+			},
+		}).Build()
+	if err := cl.Get(context.Background(), types.NamespacedName{Name: "demo"}, tmpl); err != nil {
+		t.Fatal(err)
+	}
+	r := &ModuleReconciler{Client: cl, Scheme: scrapeScheme(t), Namespace: "gp-system", EventRecorder: rec}
+
+	if err := r.applyLocales(context.Background(), tmpl, localesBundle(nil)); !errors.Is(err, boom) {
+		t.Fatalf("err = %v, want the delete error", err)
+	}
+	cond := meta.FindStatusCondition(tmpl.Status.Conditions, gameplanev1alpha1.GameTemplateConditionLocalesValid)
+	if cond == nil || cond.Status != metav1.ConditionFalse || cond.Reason != "WriteFailed" {
+		t.Fatalf("condition = %+v; want False/WriteFailed", cond)
+	}
+}
+
+func TestProblemsFingerprint_WriteErrorTextIsIgnored(t *testing.T) {
+	a := problemsFingerprint(localeOutcome{WriteErr: errors.New("timeout after 1.2s")})
+	b := problemsFingerprint(localeOutcome{WriteErr: errors.New("timeout after 3.4s")})
+	if a == "" || a != b {
+		t.Fatalf("fingerprints %q and %q; want equal and non-empty", a, b)
+	}
+}
+
+func TestBuildLocales_OversizedInvalidTagIsRejected(t *testing.T) {
+	out := buildLocalesWithOversized(localesRef(), nil, []string{"de", "not a tag"})
+	if len(out.Oversized) != 1 || out.Oversized[0] != "de" {
+		t.Fatalf("Oversized = %v; want [de]", out.Oversized)
+	}
+	if len(out.Rejected) != 1 || out.Rejected[0] != "not a tag" {
+		t.Fatalf("Rejected = %v", out.Rejected)
+	}
+}
+
+func TestLocalesCondition_MessageIsBounded(t *testing.T) {
+	tags := make([]string, 0, 5000)
+	for i := 0; i < 5000; i++ {
+		tags = append(tags, strings.Repeat("x", 8))
+	}
+	c := localesCondition(localeOutcome{Oversized: tags})
+	if len(c.Message) > maxConditionMessageBytes {
+		t.Fatalf("message length %d exceeds %d", len(c.Message), maxConditionMessageBytes)
+	}
+}
diff --git a/operator/internal/controller/module_locales_test.go b/operator/internal/controller/module_locales_test.go
new file mode 100644
index 000000000..808babb80
--- /dev/null
+++ b/operator/internal/controller/module_locales_test.go
@@ -0,0 +1,495 @@
+package controller
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+	"testing"
+
+	corev1 "k8s.io/api/core/v1"
+	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/api/meta"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/client-go/tools/events"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/client/fake"
+	"sigs.k8s.io/controller-runtime/pkg/client/interceptor"
+
+	"github.com/GameplanePanel/gameplane/i18n/pack"
+	gameplanev1alpha1 "github.com/GameplanePanel/gameplane/operator/api/v1alpha1"
+	"github.com/GameplanePanel/gameplane/operator/internal/modsrc"
+)
+
+func localesRef() map[string]pack.Entry {
+	return map[string]pack.Entry{
+		"template.displayName": {DefaultMessage: "Minecraft", Description: "d"},
+		"module.summary":       {DefaultMessage: "Summary {n}", Description: "d"},
+	}
+}
+
+func TestBuildLocales_ValidKept(t *testing.T) {
+	out := buildLocales(localesRef(), map[string][]byte{
+		"fr": []byte(`{"template.displayName":{"defaultMessage":"Minecraft FR"}}`),
+	})
+	if len(out.Problems) != 0 || len(out.Dropped) != 0 || len(out.Rejected) != 0 {
+		t.Fatalf("unexpected problems: %+v", out)
+	}
+	got, err := pack.ParseEntries([]byte(out.Data["fr.json"]))
+	if err != nil || got["template.displayName"].DefaultMessage != "Minecraft FR" {
+		t.Fatalf("fr.json = %q, %v", out.Data["fr.json"], err)
+	}
+	if status := localesCondition(out); status.Status != metav1.ConditionTrue || status.Reason != "Valid" {
+		t.Errorf("condition = %+v", status)
+	}
+}
+
+func TestBuildLocales_DropsInvalidEntries(t *testing.T) {
+	out := buildLocales(localesRef(), map[string][]byte{
+		"fr": []byte(`{
+			"template.displayName":{"defaultMessage":"Bon"},
+			"module.summary":{"defaultMessage":"{extra}"},
+			"unknown.id":{"defaultMessage":"x"}
+		}`),
+	})
+	got, err := pack.ParseEntries([]byte(out.Data["fr.json"]))
+	if err != nil || len(got) != 1 || got["template.displayName"].DefaultMessage != "Bon" {
+		t.Fatalf("fr.json = %q, %v", out.Data["fr.json"], err)
+	}
+	if out.PerLang["fr"] != 2 || len(out.Problems) < 2 {
+		t.Fatalf("outcome = %+v", out)
+	}
+	for _, p := range out.Problems {
+		if !strings.HasPrefix(p, "fr:") {
+			t.Errorf("problem %q lacks the tag prefix", p)
+		}
+	}
+	c := localesCondition(out)
+	if c.Status != metav1.ConditionFalse || c.Reason != "InvalidEntries" || c.Message != "fr: 2 entries dropped" {
+		t.Errorf("condition = %+v", c)
+	}
+}
+
+func TestBuildLocales_SingularCountAndRejectedFiles(t *testing.T) {
+	out := buildLocales(localesRef(), map[string][]byte{
+		"de":  []byte(`{"unknown.id":{"defaultMessage":"x"}}`),
+		"xx":  []byte(`not json`),
+		"BAD": []byte(`{}`),
+	})
+	if len(out.Data) != 0 {
+		t.Fatalf("Data = %v", out.Data)
+	}
+	c := localesCondition(out)
+	if !strings.Contains(c.Message, "de: 1 entry dropped") || !strings.Contains(c.Message, "xx: file rejected") ||
+		!strings.Contains(c.Message, "BAD: file rejected") {
+		t.Errorf("message = %q", c.Message)
+	}
+	joined := strings.Join(out.Problems, "\n")
+	if !strings.Contains(joined, "BAD:<pack>: invalid language tag") {
+		t.Errorf("problems = %q", joined)
+	}
+}
+
+func TestBuildLocales_DeterministicOrder(t *testing.T) {
+	layers := map[string][]byte{
+		"fr": []byte(`{"unknown.b":{"defaultMessage":"x"},"unknown.a":{"defaultMessage":"x"}}`),
+		"de": []byte(`{"unknown.c":{"defaultMessage":"x"}}`),
+	}
+	first := buildLocales(localesRef(), layers).Problems
+	for range 10 {
+		again := buildLocales(localesRef(), layers).Problems
+		if strings.Join(again, "|") != strings.Join(first, "|") {
+			t.Fatalf("non-deterministic problems:\n%v\n%v", first, again)
+		}
+	}
+	if !strings.HasPrefix(first[0], "de:") || !strings.HasPrefix(first[1], "fr:unknown.a") {
+		t.Errorf("problems not sorted by tag then id: %v", first)
+	}
+}
+
+func TestBuildLocales_SizeBoundStopsAtFirstOverflow(t *testing.T) {
+	big := strings.Repeat("x", 400*1024)
+	mk := func() []byte {
+		return []byte(fmt.Sprintf(`{"template.displayName":{"defaultMessage":%q}}`, big))
+	}
+	ref := map[string]pack.Entry{"template.displayName": {DefaultMessage: "Minecraft", Description: "d"}}
+	out := buildLocales(ref, map[string][]byte{"de": mk(), "fr": mk(), "it": mk(), "nl": []byte(`{"template.displayName":{"defaultMessage":"s"}}`)})
+	if _, ok := out.Data["de.json"]; !ok {
+		t.Error("de.json should be kept")
+	}
+	if _, ok := out.Data["fr.json"]; !ok {
+		t.Error("fr.json should be kept")
+	}
+	if len(out.Dropped) != 2 || out.Dropped[0] != "it" || out.Dropped[1] != "nl" {
+		t.Errorf("Dropped = %v; the small nl must not slip in after the overflow", out.Dropped)
+	}
+	c := localesCondition(out)
+	if c.Reason != "LocalesTooLarge" || !strings.Contains(c.Message, "it, nl") {
+		t.Errorf("condition = %+v", c)
+	}
+}
+
+func TestProblemEventNote_Truncates(t *testing.T) {
+	var problems []string
+	for i := range 25 {
+		problems = append(problems, fmt.Sprintf("fr:id%d: bad", i))
+	}
+	lines := strings.Split(problemEventNote(problems), "\n")
+	if len(lines) != maxLocaleProblems+1 || lines[len(lines)-1] != "... and 5 more" {
+		t.Fatalf("lines = %d, last = %q", len(lines), lines[len(lines)-1])
+	}
+	if got := problemEventNote(problems[:3]); strings.Contains(got, "more") {
+		t.Errorf("short note truncated: %q", got)
+	}
+}
+
+func localesBundle(layers map[string][]byte) *modsrc.Bundle {
+	return &modsrc.Bundle{
+		Metadata:     modsrc.Metadata{Name: "demo", DisplayName: "Demo", Summary: "Summary"},
+		TemplateYAML: []byte("spec:\n  displayName: Demo Game\n"),
+		Locales:      layers,
+	}
+}
+
+func newLocalesFixture(t *testing.T, rec *events.FakeRecorder) (*ModuleReconciler, *gameplanev1alpha1.GameTemplate) {
+	t.Helper()
+	tmpl := &gameplanev1alpha1.GameTemplate{ObjectMeta: metav1.ObjectMeta{Name: "demo", UID: "tmpl-uid", Generation: 2}}
+	cl := fake.NewClientBuilder().WithScheme(scrapeScheme(t)).
+		WithObjects(tmpl).
+		WithStatusSubresource(&gameplanev1alpha1.GameTemplate{}).
+		Build()
+	if err := cl.Get(context.Background(), types.NamespacedName{Name: "demo"}, tmpl); err != nil {
+		t.Fatal(err)
+	}
+	r := &ModuleReconciler{Client: cl, Scheme: scrapeScheme(t), Namespace: "gp-system"}
+	if rec != nil {
+		r.EventRecorder = rec
+	}
+	return r, tmpl
+}
+
+func getLocalesCM(t *testing.T, r *ModuleReconciler) (*corev1.ConfigMap, error) {
+	t.Helper()
+	cm := &corev1.ConfigMap{}
+	err := r.Get(context.Background(), types.NamespacedName{Namespace: "gp-system", Name: "demo-locales"}, cm)
+	return cm, err
+}
+
+func TestApplyLocales_WritesOwnedConfigMapAndWarns(t *testing.T) {
+	rec := events.NewFakeRecorder(8)
+	r, tmpl := newLocalesFixture(t, rec)
+	r.applyLocales(context.Background(), tmpl, localesBundle(map[string][]byte{
+		"fr": []byte(`{"template.displayName":{"defaultMessage":"Jeu"},"module.summary":{"defaultMessage":"{x}"}}`),
+	}))
+
+	cm, err := getLocalesCM(t, r)
+	if err != nil {
+		t.Fatalf("ConfigMap: %v", err)
+	}
+	got, err := pack.ParseEntries([]byte(cm.Data["fr.json"]))
+	if err != nil || len(got) != 1 {
+		t.Fatalf("fr.json = %q, %v", cm.Data["fr.json"], err)
+	}
+	if len(cm.OwnerReferences) != 1 || cm.OwnerReferences[0].UID != tmpl.UID || cm.OwnerReferences[0].Kind != "GameTemplate" {
+		t.Errorf("ownerReferences = %+v", cm.OwnerReferences)
+	}
+
+	stored := &gameplanev1alpha1.GameTemplate{}
+	if err := r.Get(context.Background(), types.NamespacedName{Name: "demo"}, stored); err != nil {
+		t.Fatal(err)
+	}
+	cond := meta.FindStatusCondition(stored.Status.Conditions, gameplanev1alpha1.GameTemplateConditionLocalesValid)
+	if cond == nil || cond.Status != metav1.ConditionFalse || cond.Reason != "InvalidEntries" || cond.ObservedGeneration != 2 {
+		t.Fatalf("condition = %+v", cond)
+	}
+
+	select {
+	case ev := <-rec.Events:
+		if !strings.Contains(ev, "Warning") || !strings.Contains(ev, "fr:module.summary") {
+			t.Errorf("event = %q", ev)
+		}
+	default:
+		t.Fatal("no Warning event recorded")
+	}
+
+	// A second apply with the same problem set does not repeat the event.
+	r.applyLocales(context.Background(), stored, localesBundle(map[string][]byte{
+		"fr": []byte(`{"template.displayName":{"defaultMessage":"Jeu"},"module.summary":{"defaultMessage":"{x}"}}`),
+	}))
+	select {
+	case ev := <-rec.Events:
+		t.Errorf("repeated event: %q", ev)
+	default:
+	}
+}
+
+func TestApplyLocales_AllValidSetsTrueWithoutEvent(t *testing.T) {
+	rec := events.NewFakeRecorder(8)
+	r, tmpl := newLocalesFixture(t, rec)
+	r.applyLocales(context.Background(), tmpl, localesBundle(map[string][]byte{
+		"fr": []byte(`{"template.displayName":{"defaultMessage":"Jeu"}}`),
+	}))
+	cond := meta.FindStatusCondition(tmpl.Status.Conditions, gameplanev1alpha1.GameTemplateConditionLocalesValid)
+	if cond == nil || cond.Status != metav1.ConditionTrue {
+		t.Fatalf("condition = %+v", cond)
+	}
+	if len(rec.Events) != 0 {
+		t.Error("unexpected event")
+	}
+}
+
+func TestApplyLocales_RemovesConfigMapWhenNothingValid(t *testing.T) {
+	r, tmpl := newLocalesFixture(t, nil)
+	r.applyLocales(context.Background(), tmpl, localesBundle(map[string][]byte{
+		"fr": []byte(`{"template.displayName":{"defaultMessage":"Jeu"}}`),
+	}))
+	if _, err := getLocalesCM(t, r); err != nil {
+		t.Fatalf("ConfigMap should exist: %v", err)
+	}
+	r.applyLocales(context.Background(), tmpl, localesBundle(map[string][]byte{
+		"fr": []byte(`{"unknown.id":{"defaultMessage":"x"}}`),
+	}))
+	if _, err := getLocalesCM(t, r); !apierrors.IsNotFound(err) {
+		t.Fatalf("ConfigMap should be gone, err = %v", err)
+	}
+}
+
+func TestApplyLocales_NoLayersIsNoOpAndClearsStaleState(t *testing.T) {
+	r, tmpl := newLocalesFixture(t, nil)
+	// Nothing to do on a bundle without locales.
+	r.applyLocales(context.Background(), tmpl, localesBundle(nil))
+	if _, err := getLocalesCM(t, r); !apierrors.IsNotFound(err) {
+		t.Fatalf("unexpected ConfigMap, err = %v", err)
+	}
+	if len(tmpl.Status.Conditions) != 0 {
+		t.Fatalf("unexpected conditions %v", tmpl.Status.Conditions)
+	}
+
+	// An older version shipped translations; the new one ships none.
+	r.applyLocales(context.Background(), tmpl, localesBundle(map[string][]byte{
+		"fr": []byte(`{"template.displayName":{"defaultMessage":"Jeu"}}`),
+	}))
+	r.applyLocales(context.Background(), tmpl, localesBundle(nil))
+	if _, err := getLocalesCM(t, r); !apierrors.IsNotFound(err) {
+		t.Fatalf("stale ConfigMap remained, err = %v", err)
+	}
+	if c := meta.FindStatusCondition(tmpl.Status.Conditions, gameplanev1alpha1.GameTemplateConditionLocalesValid); c != nil {
+		t.Fatalf("stale condition remained: %+v", c)
+	}
+}
+
+func TestApplyLocales_TooLargeWarnsAboutDroppedLanguages(t *testing.T) {
+	rec := events.NewFakeRecorder(8)
+	r, tmpl := newLocalesFixture(t, rec)
+	big := strings.Repeat("x", 500*1024)
+	layer := []byte(fmt.Sprintf(`{"template.displayName":{"defaultMessage":%q}}`, big))
+	r.applyLocales(context.Background(), tmpl, localesBundle(map[string][]byte{"de": layer, "fr": layer}))
+
+	cond := meta.FindStatusCondition(tmpl.Status.Conditions, gameplanev1alpha1.GameTemplateConditionLocalesValid)
+	if cond == nil || cond.Reason != "LocalesTooLarge" {
+		t.Fatalf("condition = %+v", cond)
+	}
+	cm, err := getLocalesCM(t, r)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := cm.Data["de.json"]; !ok || len(cm.Data) != 1 {
+		t.Errorf("ConfigMap keys = %v; want only de.json", cm.Data)
+	}
+	if ev := <-rec.Events; !strings.Contains(ev, "LocalesTooLarge") || !strings.Contains(ev, "fr") {
+		t.Errorf("event = %q", ev)
+	}
+}
+
+func TestApplyLocales_NilRecorderAndNilInputsAreSafe(t *testing.T) {
+	r, tmpl := newLocalesFixture(t, nil)
+	r.applyLocales(context.Background(), nil, localesBundle(nil))
+	r.applyLocales(context.Background(), tmpl, nil)
+	r.applyLocales(context.Background(), tmpl, localesBundle(map[string][]byte{
+		"fr": []byte(`{"unknown.id":{"defaultMessage":"x"}}`),
+	}))
+}
+
+func TestApplyLocales_BadTemplateYAMLIsLoggedNotFatal(t *testing.T) {
+	r, tmpl := newLocalesFixture(t, nil)
+	b := localesBundle(map[string][]byte{"fr": []byte(`{}`)})
+	b.TemplateYAML = []byte("spec: [broken")
+	r.applyLocales(context.Background(), tmpl, b)
+	if _, err := getLocalesCM(t, r); !apierrors.IsNotFound(err) {
+		t.Fatalf("ConfigMap written for an unparsable template, err = %v", err)
+	}
+}
+
+func TestLocalesNamespaceDefault(t *testing.T) {
+	if got := (&ModuleReconciler{}).localesNamespace(); got != "gameplane-system" {
+		t.Errorf("default namespace = %q", got)
+	}
+	if got := (&ModuleReconciler{Namespace: "x"}).localesNamespace(); got != "x" {
+		t.Errorf("namespace = %q", got)
+	}
+}
+
+func drainEvents(rec *events.FakeRecorder) []string {
+	var out []string
+	for {
+		select {
+		case ev := <-rec.Events:
+			out = append(out, ev)
+		default:
+			return out
+		}
+	}
+}
+
+func TestApplyLocales_OversizedLayerIsReportedNotDropped(t *testing.T) {
+	rec := events.NewFakeRecorder(8)
+	r, tmpl := newLocalesFixture(t, rec)
+	b := localesBundle(map[string][]byte{"fr": []byte(`{"template.displayName":{"defaultMessage":"Jeu"}}`)})
+	b.OversizedLocales = []string{"de"}
+	if err := r.applyLocales(context.Background(), tmpl, b); err != nil {
+		t.Fatal(err)
+	}
+	cond := meta.FindStatusCondition(tmpl.Status.Conditions, gameplanev1alpha1.GameTemplateConditionLocalesValid)
+	if cond == nil || cond.Status != metav1.ConditionFalse || cond.Reason != "LocalesTooLarge" || !strings.Contains(cond.Message, "de") {
+		t.Fatalf("condition = %+v", cond)
+	}
+	cm, err := getLocalesCM(t, r)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := cm.Data["fr.json"]; !ok || len(cm.Data) != 1 {
+		t.Errorf("ConfigMap keys = %v; want fr.json only", cm.Data)
+	}
+	evs := drainEvents(rec)
+	found := false
+	for _, ev := range evs {
+		if strings.Contains(ev, "Warning") && strings.Contains(ev, "LocalesTooLarge") && strings.Contains(ev, "de") {
+			found = true
+		}
+	}
+	if !found {
+		t.Errorf("events = %q; want a LocalesTooLarge warning naming de", evs)
+	}
+}
+
+func TestApplyLocales_OnlyOversizedKeepsConditionAndNoConfigMap(t *testing.T) {
+	r, tmpl := newLocalesFixture(t, nil)
+	b := localesBundle(nil)
+	b.OversizedLocales = []string{"de"}
+	if err := r.applyLocales(context.Background(), tmpl, b); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := getLocalesCM(t, r); !apierrors.IsNotFound(err) {
+		t.Fatalf("ConfigMap should be absent, err = %v", err)
+	}
+	cond := meta.FindStatusCondition(tmpl.Status.Conditions, gameplanev1alpha1.GameTemplateConditionLocalesValid)
+	if cond == nil || cond.Status != metav1.ConditionFalse || cond.Reason != "LocalesTooLarge" {
+		t.Fatalf("condition = %+v; want False/LocalesTooLarge", cond)
+	}
+}
+
+func TestApplyLocales_WriteFailureIsReported(t *testing.T) {
+	rec := events.NewFakeRecorder(8)
+	tmpl := &gameplanev1alpha1.GameTemplate{ObjectMeta: metav1.ObjectMeta{Name: "demo", UID: "tmpl-uid", Generation: 2}}
+	boom := errors.New("boom")
+	cl := fake.NewClientBuilder().WithScheme(scrapeScheme(t)).
+		WithObjects(tmpl).
+		WithStatusSubresource(&gameplanev1alpha1.GameTemplate{}).
+		WithInterceptorFuncs(interceptor.Funcs{
+			Create: func(ctx context.Context, c client.WithWatch, obj client.Object, opts ...client.CreateOption) error {
+				if _, ok := obj.(*corev1.ConfigMap); ok {
+					return boom
+				}
+				return c.Create(ctx, obj, opts...)
+			},
+		}).Build()
+	if err := cl.Get(context.Background(), types.NamespacedName{Name: "demo"}, tmpl); err != nil {
+		t.Fatal(err)
+	}
+	r := &ModuleReconciler{Client: cl, Scheme: scrapeScheme(t), Namespace: "gp-system", EventRecorder: rec}
+
+	err := r.applyLocales(context.Background(), tmpl, localesBundle(map[string][]byte{
+		"fr": []byte(`{"template.displayName":{"defaultMessage":"Jeu"}}`),
+	}))
+	if !errors.Is(err, boom) {
+		t.Fatalf("err = %v, want the write error", err)
+	}
+	cond := meta.FindStatusCondition(tmpl.Status.Conditions, gameplanev1alpha1.GameTemplateConditionLocalesValid)
+	if cond == nil || cond.Status != metav1.ConditionFalse || cond.Reason != "WriteFailed" {
+		t.Fatalf("condition = %+v; want False/WriteFailed", cond)
+	}
+	found := false
+	for _, ev := range drainEvents(rec) {
+		if strings.Contains(ev, "LocalesWriteFailed") {
+			found = true
+		}
+	}
+	if !found {
+		t.Error("no LocalesWriteFailed event")
+	}
+}
+
+func TestLocalesCondition_ReasonPriority(t *testing.T) {
+	cases := []struct {
+		name   string
+		out    localeOutcome
+		status metav1.ConditionStatus
+		reason string
+	}{
+		{"all three", localeOutcome{WriteErr: errors.New("x"), Dropped: []string{"fr"}, PerLang: map[string]int{"de": 1}}, metav1.ConditionFalse, "WriteFailed"},
+		{"too large and invalid", localeOutcome{Oversized: []string{"fr"}, PerLang: map[string]int{"de": 1}}, metav1.ConditionFalse, "LocalesTooLarge"},
+		{"invalid", localeOutcome{PerLang: map[string]int{"de": 1}}, metav1.ConditionFalse, "InvalidEntries"},
+		{"none", localeOutcome{}, metav1.ConditionTrue, "Valid"},
+	}
+	for _, c := range cases {
+		got := localesCondition(c.out)
+		if got.Status != c.status || got.Reason != c.reason {
+			t.Errorf("%s: got %s/%s, want %s/%s", c.name, got.Status, got.Reason, c.status, c.reason)
+		}
+	}
+	if got := localesCondition(localeOutcome{}); got.Message != "All module translations are valid." {
+		t.Errorf("message = %q", got.Message)
+	}
+	if got := localesCondition(localeOutcome{Oversized: []string{"fr", "de"}}); !strings.Contains(got.Message, "fr, de") {
+		t.Errorf("message = %q", got.Message)
+	}
+}
+
+func TestApplyLocales_EventsFireOnlyWhenProblemListChanges(t *testing.T) {
+	rec := events.NewFakeRecorder(16)
+	r, tmpl := newLocalesFixture(t, rec)
+	bad := func(id string) *modsrc.Bundle {
+		return localesBundle(map[string][]byte{"fr": []byte(fmt.Sprintf(`{"template.displayName":{"defaultMessage":"Jeu"},%q:{"defaultMessage":"x"}}`, id))})
+	}
+	apply := func(b *modsrc.Bundle) {
+		t.Helper()
+		if err := r.applyLocales(context.Background(), tmpl, b); err != nil {
+			t.Fatal(err)
+		}
+	}
+	count := func() int { return len(drainEvents(rec)) }
+
+	apply(bad("unknown.a"))
+	apply(bad("unknown.a"))
+	if n := count(); n != 1 {
+		t.Fatalf("same problems twice: %d events, want 1", n)
+	}
+	// Same counts, different ids: the list changed.
+	apply(bad("unknown.b"))
+	if n := count(); n != 1 {
+		t.Fatalf("changed ids with identical counts: %d events, want 1", n)
+	}
+	// Problems, then none, then the same problems again: the list changed twice.
+	apply(localesBundle(map[string][]byte{"fr": []byte(`{"template.displayName":{"defaultMessage":"Jeu"}}`)}))
+	if tmpl.Annotations[localesProblemsAnnotation] != "" {
+		t.Errorf("annotation = %q, want removed", tmpl.Annotations[localesProblemsAnnotation])
+	}
+	if n := count(); n != 0 {
+		t.Fatalf("valid bundle: %d events, want 0", n)
+	}
+	apply(bad("unknown.b"))
+	if n := count(); n != 1 {
+		t.Fatalf("problems after a clean pull: %d events, want 1", n)
+	}
+}
diff --git a/operator/internal/modsrc/bundle.go b/operator/internal/modsrc/bundle.go
index 92731947d..8c7f735d1 100644
--- a/operator/internal/modsrc/bundle.go
+++ b/operator/internal/modsrc/bundle.go
@@ -10,6 +10,7 @@ import (
 	"errors"
 	"fmt"
 
+	"github.com/GameplanePanel/gameplane/operator/internal/oci"
 	"sigs.k8s.io/yaml"
 )
 
@@ -69,6 +70,18 @@ type Bundle struct {
 	// Currently surfaced via the API by base64-encoding into a data
 	// URI, sized down by the caller.
 	Icon []byte
+
+	// Locales holds the module's translation files, keyed by language tag
+	// (from "locales/<tag>.json" layers). It is nil for bundles that carry
+	// none. The content is unvalidated; the Module reconciler checks it
+	// against the ids derived from the template.
+	Locales map[string][]byte
+
+	// OversizedLocales lists, sorted, the tags whose locale file was larger
+	// than oci.MaxLocaleLayerSize, or did not fit oci.MaxLocaleTotalSize, and
+	// was therefore not read. Locales never
+	// holds them; the reconciler reports them as LocalesTooLarge.
+	OversizedLocales []string
 }
 
 // FromFiles assembles and validates a Bundle from its files, keyed by
@@ -94,6 +107,11 @@ func FromFiles(digest string, files map[string][]byte) (*Bundle, error) {
 	b.TemplateYAML = tmpl
 	b.Readme = files[FileReadme]
 	b.Icon = files[FileIcon]
+	locales, oversized := oci.SplitLocaleLayers(files)
+	if len(locales) > 0 {
+		b.Locales = locales
+	}
+	b.OversizedLocales = oversized
 	return b, nil
 }
 
diff --git a/operator/internal/modsrc/bundle_locales_test.go b/operator/internal/modsrc/bundle_locales_test.go
new file mode 100644
index 000000000..cc5799b5e
--- /dev/null
+++ b/operator/internal/modsrc/bundle_locales_test.go
@@ -0,0 +1,58 @@
+package modsrc
+
+import (
+	"testing"
+
+	"github.com/GameplanePanel/gameplane/operator/internal/oci"
+)
+
+const localesTestMetadata = "name: demo\ndisplayName: Demo\nversion: 1.0.0\n"
+
+func TestFromFilesCollectsLocales(t *testing.T) {
+	t.Parallel()
+	b, err := FromFiles("sha256:x", map[string][]byte{
+		FileMetadata:      []byte(localesTestMetadata),
+		FileTemplate:      []byte("spec: {}\n"),
+		"locales/fr.json": []byte(`{"a":{"defaultMessage":"x"}}`),
+		"locales/en.json": []byte(`{}`),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(b.Locales) != 1 || string(b.Locales["fr"]) != `{"a":{"defaultMessage":"x"}}` {
+		t.Fatalf("Locales = %v", b.Locales)
+	}
+}
+
+func TestFromFilesWithoutLocalesIsNil(t *testing.T) {
+	t.Parallel()
+	b, err := FromFiles("sha256:x", map[string][]byte{
+		FileMetadata: []byte(localesTestMetadata),
+		FileTemplate: []byte("spec: {}\n"),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if b.Locales != nil {
+		t.Fatalf("Locales = %v, want nil", b.Locales)
+	}
+}
+
+func TestFromFilesRecordsOversizedLocales(t *testing.T) {
+	t.Parallel()
+	b, err := FromFiles("sha256:x", map[string][]byte{
+		FileMetadata:      []byte(localesTestMetadata),
+		FileTemplate:      []byte("spec: {}\n"),
+		"locales/fr.json": []byte(`{}`),
+		"locales/de.json": oci.OversizedLocale,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(b.OversizedLocales) != 1 || b.OversizedLocales[0] != "de" {
+		t.Fatalf("OversizedLocales = %v, want [de]", b.OversizedLocales)
+	}
+	if _, ok := b.Locales["de"]; ok || len(b.Locales) != 1 {
+		t.Fatalf("Locales = %v, want fr only", b.Locales)
+	}
+}
diff --git a/operator/internal/modsrc/dir.go b/operator/internal/modsrc/dir.go
index c01b671b6..ed0d08ce8 100644
--- a/operator/internal/modsrc/dir.go
+++ b/operator/internal/modsrc/dir.go
@@ -9,8 +9,10 @@ import (
 	"io/fs"
 	"path"
 	"sort"
+	"strings"
 
 	gameplanev1alpha1 "github.com/GameplanePanel/gameplane/operator/api/v1alpha1"
+	"github.com/GameplanePanel/gameplane/operator/internal/oci"
 )
 
 // newFSFetcher builds a Fetcher over any filesystem-shaped source —
@@ -148,6 +150,7 @@ func bundleFromDir(fsys fs.FS, dir, digest string) (*Bundle, error) {
 		}
 		files[name] = data
 	}
+	readLocaleFiles(fsys, dir, files)
 	if digest == "" {
 		var err error
 		if digest, err = contentDigest(fsys, dir); err != nil {
@@ -157,6 +160,61 @@ func bundleFromDir(fsys fs.FS, dir, digest string) (*Bundle, error) {
 	return FromFiles(digest, files)
 }
 
+// readLocaleFiles adds locales/<tag>.json (regular files only) to files under
+// the key "locales/<tag>.json", the same names an OCI bundle uses. A file over
+// oci.MaxLocaleLayerSize is not read: oci.OversizedLocale is stored in its
+// place so the reconciler reports the language instead of dropping it. The
+// files together are also bounded by oci.MaxLocaleTotalSize: languages are
+// counted in name order, and one that would exceed the total is recorded as
+// oversized the same way.
+func readLocaleFiles(fsys fs.FS, dir string, files map[string][]byte) {
+	entries, err := fs.ReadDir(fsys, path.Join(dir, "locales"))
+	if err != nil {
+		return
+	}
+	var budget oci.LocaleBudget
+	for _, e := range entries {
+		name := e.Name()
+		if !e.Type().IsRegular() || !strings.HasSuffix(name, ".json") {
+			continue
+		}
+		key := oci.LocaleLayerPrefix + name
+		info, err := e.Info()
+		if err != nil {
+			continue
+		}
+		if info.Size() > oci.MaxLocaleLayerSize || !budget.Take(info.Size()) {
+			files[key] = oci.OversizedLocale
+			continue
+		}
+		data, err := readFileCapped(fsys, path.Join(dir, key), oci.MaxLocaleLayerSize)
+		if err != nil {
+			continue
+		}
+		if len(data) > oci.MaxLocaleLayerSize {
+			// The file grew after the size check; the cap still holds.
+			files[key] = oci.OversizedLocale
+			continue
+		}
+		files[key] = data
+	}
+}
+
+// readFileCapped reads at most limit+1 bytes of name, so a caller can tell a file
+// over limit apart without holding more than that in memory.
+func readFileCapped(fsys fs.FS, name string, limit int64) ([]byte, error) {
+	f, err := fsys.Open(name)
+	if err != nil {
+		return nil, fmt.Errorf("open %s: %w", name, err)
+	}
+	defer func() { _ = f.Close() }()
+	data, err := io.ReadAll(io.LimitReader(f, limit+1))
+	if err != nil {
+		return nil, fmt.Errorf("read %s: %w", name, err)
+	}
+	return data, nil
+}
+
 // contentDigest hashes every regular file under dir — relative path
 // and bytes — in the deterministic lexical order fs.WalkDir guarantees,
 // so identical content always yields the same digest regardless of
diff --git a/operator/internal/modsrc/dir_locales_budget_test.go b/operator/internal/modsrc/dir_locales_budget_test.go
new file mode 100644
index 000000000..97d773ba0
--- /dev/null
+++ b/operator/internal/modsrc/dir_locales_budget_test.go
@@ -0,0 +1,46 @@
+package modsrc
+
+import (
+	"bytes"
+	"testing"
+	"testing/fstest"
+
+	"github.com/GameplanePanel/gameplane/operator/internal/oci"
+)
+
+func TestReadLocaleFilesTotalBudget(t *testing.T) {
+	body := bytes.Repeat([]byte("x"), 800*1024)
+	fsys := fstest.MapFS{}
+	for _, tag := range []string{"aa", "bb", "cc", "dd", "ee", "ff"} {
+		fsys["m/locales/"+tag+".json"] = &fstest.MapFile{Data: body}
+	}
+	files := map[string][]byte{}
+	readLocaleFiles(fsys, "m", files)
+
+	locales, oversized := oci.SplitLocaleLayers(files)
+	if len(locales) != 5 {
+		t.Errorf("read %d locale files, want 5", len(locales))
+	}
+	if len(oversized) != 1 || oversized[0] != "ff" {
+		t.Errorf("oversized = %v, want [ff]", oversized)
+	}
+}
+
+func TestReadLocaleFilesSmallerLanguageStillFits(t *testing.T) {
+	big := bytes.Repeat([]byte("x"), 800*1024)
+	fsys := fstest.MapFS{}
+	for _, tag := range []string{"aa", "bb", "cc", "dd", "ee"} {
+		fsys["m/locales/"+tag+".json"] = &fstest.MapFile{Data: big}
+	}
+	fsys["m/locales/ff.json"] = &fstest.MapFile{Data: big}
+	fsys["m/locales/gg.json"] = &fstest.MapFile{Data: []byte(`{}`)}
+	files := map[string][]byte{}
+	readLocaleFiles(fsys, "m", files)
+
+	if !oci.IsOversizedLocale(files["locales/ff.json"]) {
+		t.Error("ff should be oversized")
+	}
+	if string(files["locales/gg.json"]) != `{}` {
+		t.Errorf("gg = %q, want the small file read", files["locales/gg.json"])
+	}
+}
diff --git a/operator/internal/modsrc/dir_locales_capped_test.go b/operator/internal/modsrc/dir_locales_capped_test.go
new file mode 100644
index 000000000..c7acbe308
--- /dev/null
+++ b/operator/internal/modsrc/dir_locales_capped_test.go
@@ -0,0 +1,26 @@
+package modsrc
+
+import (
+	"bytes"
+	"testing"
+	"testing/fstest"
+
+	"github.com/GameplanePanel/gameplane/operator/internal/oci"
+)
+
+func TestReadFileCapped(t *testing.T) {
+	fsys := fstest.MapFS{"f": &fstest.MapFile{Data: bytes.Repeat([]byte("x"), 10)}}
+	got, err := readFileCapped(fsys, "f", 4)
+	if err != nil || len(got) != 5 {
+		t.Fatalf("readFileCapped = %d bytes, %v; want 5 bytes", len(got), err)
+	}
+	if _, err := readFileCapped(fsys, "missing", 4); err == nil {
+		t.Fatal("missing file: want an error")
+	}
+	files := map[string][]byte{}
+	big := fstest.MapFS{"m/locales/de.json": &fstest.MapFile{Data: bytes.Repeat([]byte("x"), oci.MaxLocaleLayerSize+1)}}
+	readLocaleFiles(big, "m", files)
+	if !oci.IsOversizedLocale(files["locales/de.json"]) {
+		t.Fatalf("oversized file was not marked")
+	}
+}
diff --git a/operator/internal/modsrc/dir_locales_test.go b/operator/internal/modsrc/dir_locales_test.go
new file mode 100644
index 000000000..687222cc5
--- /dev/null
+++ b/operator/internal/modsrc/dir_locales_test.go
@@ -0,0 +1,61 @@
+package modsrc
+
+import (
+	"context"
+	"strings"
+	"testing"
+	"testing/fstest"
+
+	"github.com/GameplanePanel/gameplane/operator/internal/oci"
+)
+
+func localesFS(frBody string) fstest.MapFS {
+	fsys := moduleDirFS(map[string]map[string]string{"mc": validModuleFiles("mc", "1.0.0")})
+	fsys["mc/locales/fr.json"] = &fstest.MapFile{Data: []byte(frBody)}
+	fsys["mc/locales/en.json"] = &fstest.MapFile{Data: []byte(`{}`)}
+	fsys["mc/locales/sub/x.json"] = &fstest.MapFile{Data: []byte(`{}`)}
+	fsys["mc/locales/readme.txt"] = &fstest.MapFile{Data: []byte(`hi`)}
+	fsys["mc/locales/de.json"] = &fstest.MapFile{Data: []byte(strings.Repeat("x", oci.MaxLocaleLayerSize+1))}
+	return fsys
+}
+
+func TestBundleFromDirReadsLocaleFiles(t *testing.T) {
+	t.Parallel()
+	b, err := bundleFromDir(localesFS(`{"a":1}`), "mc", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(b.Locales) != 1 || string(b.Locales["fr"]) != `{"a":1}` {
+		t.Fatalf("Locales = %v, want fr only", b.Locales)
+	}
+	if len(b.OversizedLocales) != 1 || b.OversizedLocales[0] != "de" {
+		t.Fatalf("OversizedLocales = %v, want [de]", b.OversizedLocales)
+	}
+}
+
+func TestBundleFromDirDigestTracksLocaleChanges(t *testing.T) {
+	t.Parallel()
+	a, err := bundleFromDir(localesFS(`{"a":1}`), "mc", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	b, err := bundleFromDir(localesFS(`{"a":2}`), "mc", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if a.Digest == b.Digest {
+		t.Fatal("digest did not change when fr.json changed")
+	}
+}
+
+func TestFSFetcherPullCarriesLocales(t *testing.T) {
+	t.Parallel()
+	f := newFSFetcher(staticFS(localesFS(`{"a":1}`), ""), "local:x", nil)
+	b, err := f.Pull(context.Background(), "mc", "1.0.0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(b.Locales["fr"]) != `{"a":1}` || len(b.OversizedLocales) != 1 {
+		t.Fatalf("bundle locales = %v oversized = %v", b.Locales, b.OversizedLocales)
+	}
+}
diff --git a/operator/internal/modsrc/http_locales_test.go b/operator/internal/modsrc/http_locales_test.go
new file mode 100644
index 000000000..af453cdf2
--- /dev/null
+++ b/operator/internal/modsrc/http_locales_test.go
@@ -0,0 +1,42 @@
+package modsrc
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"testing"
+)
+
+func TestExtractArchiveCarriesLocales(t *testing.T) {
+	t.Parallel()
+	var buf bytes.Buffer
+	gz := gzip.NewWriter(&buf)
+	tw := tar.NewWriter(gz)
+	files := validModuleFiles("mc", "1.0.0")
+	files["locales/fr.json"] = `{"a":1}`
+	for name, body := range files {
+		if err := tw.WriteHeader(&tar.Header{Name: "mc/" + name, Mode: 0o600, Size: int64(len(body)), Typeflag: tar.TypeReg}); err != nil {
+			t.Fatal(err)
+		}
+		if _, err := tw.Write([]byte(body)); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if err := tw.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if err := gz.Close(); err != nil {
+		t.Fatal(err)
+	}
+	fsys, err := extractArchive(buf.Bytes())
+	if err != nil {
+		t.Fatal(err)
+	}
+	b, err := bundleFromDir(fsys, "mc", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(b.Locales["fr"]) != `{"a":1}` {
+		t.Fatalf("Locales = %v", b.Locales)
+	}
+}
diff --git a/operator/internal/modsrc/upload.go b/operator/internal/modsrc/upload.go
index feb5814c8..91236ad97 100644
--- a/operator/internal/modsrc/upload.go
+++ b/operator/internal/modsrc/upload.go
@@ -7,11 +7,13 @@ import (
 	"fmt"
 	"io"
 	"sort"
+	"strings"
 
 	corev1 "k8s.io/api/core/v1"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 
 	gameplanev1alpha1 "github.com/GameplanePanel/gameplane/operator/api/v1alpha1"
+	"github.com/GameplanePanel/gameplane/operator/internal/oci"
 )
 
 // newUpload builds a Fetcher over uploaded module bundles: ConfigMaps
@@ -101,7 +103,7 @@ func (f *uploadFetcher) scan(ctx context.Context) ([]uploadedBundle, []string, e
 				files[name] = []byte(s)
 			}
 		}
-		bundle, err := FromFiles(digestFiles(files), files)
+		bundle, err := FromFiles(digestFiles(files), uploadBundleFiles(files))
 		if err != nil {
 			warnings = append(warnings, fmt.Sprintf("upload:%s: %v", cm.Name, err))
 			continue
@@ -121,6 +123,35 @@ func (f *uploadFetcher) scan(ctx context.Context) ([]uploadedBundle, []string, e
 	return bundles, warnings, nil
 }
 
+// uploadLocaleKeyPrefix and uploadLocaleKeySuffix frame the ConfigMap key of
+// an uploaded translation file: "locales.<tag>.json". ConfigMap keys cannot
+// contain "/", so this stands for the bundle path "locales/<tag>.json".
+const (
+	uploadLocaleKeyPrefix = "locales."
+	uploadLocaleKeySuffix = ".json"
+)
+
+// uploadBundleFiles returns files with the locales.<tag>.json ConfigMap keys
+// renamed to the canonical locales/<tag>.json names FromFiles reads. A file over
+// oci.MaxLocaleLayerSize is replaced by oci.OversizedLocale so the reconciler
+// reports it. The input map is not modified (the digest covers the original).
+func uploadBundleFiles(files map[string][]byte) map[string][]byte {
+	out := make(map[string][]byte, len(files))
+	for name, data := range files {
+		if strings.HasPrefix(name, uploadLocaleKeyPrefix) && strings.HasSuffix(name, uploadLocaleKeySuffix) &&
+			len(name) > len(uploadLocaleKeyPrefix)+len(uploadLocaleKeySuffix) {
+			tag := name[len(uploadLocaleKeyPrefix) : len(name)-len(uploadLocaleKeySuffix)]
+			if len(data) > oci.MaxLocaleLayerSize {
+				data = oci.OversizedLocale
+			}
+			out[oci.LocaleLayerPrefix+tag+oci.LocaleLayerSuffix] = data
+			continue
+		}
+		out[name] = data
+	}
+	return out
+}
+
 // digestFiles is the map-shaped sibling of contentDigest: a
 // deterministic hash over sorted filename+content pairs.
 func digestFiles(files map[string][]byte) string {
diff --git a/operator/internal/modsrc/upload_locales_test.go b/operator/internal/modsrc/upload_locales_test.go
new file mode 100644
index 000000000..a57de75b5
--- /dev/null
+++ b/operator/internal/modsrc/upload_locales_test.go
@@ -0,0 +1,44 @@
+package modsrc
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/GameplanePanel/gameplane/operator/internal/oci"
+)
+
+func TestUploadFetcherPullCarriesLocales(t *testing.T) {
+	t.Parallel()
+	files := validModuleFiles("mc", "1.0.0")
+	files["locales.fr.json"] = `{"a":1}`
+	files["locales.pt-BR.json"] = `{"b":2}`
+	files["locales.de.json"] = strings.Repeat("x", oci.MaxLocaleLayerSize+1)
+	f := newUpload(uploadClient(uploadCM("bundle-mc", files)), "gameplane-system", nil)
+
+	b, err := f.Pull(context.Background(), "mc", "1.0.0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(b.Locales["fr"]) != `{"a":1}` || string(b.Locales["pt-BR"]) != `{"b":2}` || len(b.Locales) != 2 {
+		t.Fatalf("Locales = %v", b.Locales)
+	}
+	if len(b.OversizedLocales) != 1 || b.OversizedLocales[0] != "de" {
+		t.Fatalf("OversizedLocales = %v", b.OversizedLocales)
+	}
+}
+
+func TestUploadBundleFilesKeepsOriginal(t *testing.T) {
+	t.Parallel()
+	in := map[string][]byte{FileMetadata: []byte("m"), "locales.fr.json": []byte("x"), "locales..json": []byte("y")}
+	out := uploadBundleFiles(in)
+	if _, ok := out["locales/fr.json"]; !ok {
+		t.Errorf("locales/fr.json missing: %v", out)
+	}
+	if _, ok := in["locales/fr.json"]; ok {
+		t.Error("input map modified")
+	}
+	if _, ok := out["locales..json"]; !ok {
+		t.Error("empty-tag key should be left untouched")
+	}
+}
diff --git a/operator/internal/oci/bundle.go b/operator/internal/oci/bundle.go
index e43138c58..828d96947 100644
--- a/operator/internal/oci/bundle.go
+++ b/operator/internal/oci/bundle.go
@@ -5,6 +5,11 @@
 // internal/modsrc, which consumes the raw layers returned by Pull.
 package oci
 
+import (
+	"bytes"
+	"sort"
+)
+
 // Media types for the Gameplane module artifact format. The full
 // specification is in docs/module-authoring.md.
 const (
@@ -14,6 +19,7 @@ const (
 	MediaTypeTemplate = "application/vnd.gameplane.module.template.v1+yaml"
 	MediaTypeReadme   = "application/vnd.gameplane.module.readme.v1+md"
 	MediaTypeIconPNG  = "image/png"
+	MediaTypeLocale   = "application/vnd.gameplane.module.locale.v1+json"
 
 	// AnnotationTitle is the OCI annotation that carries each layer's
 	// filename inside the bundle (e.g. "module.yaml"). Pull keys the
@@ -29,3 +35,97 @@ const (
 	LayerNameReadme   = "README.md"
 	LayerNameIcon     = "icon.png"
 )
+
+// Locale layers carry module translations. Each is titled
+// "locales/<tag>.json" and typed MediaTypeLocale.
+const (
+	LocaleLayerPrefix = "locales/"
+	LocaleLayerSuffix = ".json"
+
+	// MaxLocaleLayerSize bounds one locale layer. Pull refuses to read a
+	// larger one, so a hostile bundle cannot exhaust the operator's memory.
+	MaxLocaleLayerSize = 900 * 1024
+
+	// MaxLocaleTotalSize bounds all locale files of one bundle together.
+	// Languages are counted in file-name order; one that would push the running
+	// total over this bound is recorded as oversized and not read, like a file
+	// over MaxLocaleLayerSize.
+	MaxLocaleTotalSize = 4 * 1024 * 1024
+)
+
+// LocaleBudget tracks the total bytes of locale files read for one bundle.
+type LocaleBudget struct {
+	used int64
+}
+
+// Take reserves size bytes and reports whether they fit within
+// MaxLocaleTotalSize. A size that does not fit reserves nothing, so a smaller
+// later language can still fit.
+func (b *LocaleBudget) Take(size int64) bool {
+	if size < 0 || b.used+size > MaxLocaleTotalSize {
+		return false
+	}
+	b.used += size
+	return true
+}
+
+// OversizedLocale is stored in Pull's title-keyed map in place of a locale
+// layer larger than MaxLocaleLayerSize. The blob is never read; the marker lets
+// the reconciler report the language instead of losing it silently. A real file
+// equal to this text is not valid JSON, so it cannot collide with content.
+var OversizedLocale = []byte("gameplane:oversized-locale")
+
+// IsOversizedLocale reports whether data is the OversizedLocale marker.
+func IsOversizedLocale(data []byte) bool {
+	return bytes.Equal(data, OversizedLocale)
+}
+
+// SplitLocaleLayers separates the oversized markers from the locale layers in
+// files (Pull's title-keyed map). locales holds tag -> bytes like LocaleLayers
+// without the markers; oversized lists the tags whose file was too large, sorted.
+// The English reference "en" is skipped in both.
+func SplitLocaleLayers(files map[string][]byte) (locales map[string][]byte, oversized []string) {
+	locales = map[string][]byte{}
+	for tag, data := range LocaleLayers(files) {
+		if IsOversizedLocale(data) {
+			oversized = append(oversized, tag)
+			continue
+		}
+		locales[tag] = data
+	}
+	sort.Strings(oversized)
+	return locales, oversized
+}
+
+// LocaleTag returns the language tag of a locale layer title of the form
+// "locales/<tag>.json". The tag is not validated here.
+func LocaleTag(title string) (string, bool) {
+	if len(title) <= len(LocaleLayerPrefix)+len(LocaleLayerSuffix) {
+		return "", false
+	}
+	if title[:len(LocaleLayerPrefix)] != LocaleLayerPrefix || title[len(title)-len(LocaleLayerSuffix):] != LocaleLayerSuffix {
+		return "", false
+	}
+	tag := title[len(LocaleLayerPrefix) : len(title)-len(LocaleLayerSuffix)]
+	for i := 0; i < len(tag); i++ {
+		if tag[i] == '/' {
+			return "", false
+		}
+	}
+	return tag, true
+}
+
+// LocaleLayers returns tag -> bytes for every locale layer in files (Pull's
+// title-keyed map). The English reference "en" is skipped: it is derived from
+// the template, never shipped.
+func LocaleLayers(files map[string][]byte) map[string][]byte {
+	out := map[string][]byte{}
+	for title, data := range files {
+		tag, ok := LocaleTag(title)
+		if !ok || tag == "en" {
+			continue
+		}
+		out[tag] = data
+	}
+	return out
+}
diff --git a/operator/internal/oci/client.go b/operator/internal/oci/client.go
index 477d55937..12fe2a24f 100644
--- a/operator/internal/oci/client.go
+++ b/operator/internal/oci/client.go
@@ -124,11 +124,31 @@ func (c *Client) Pull(ctx context.Context, ref, reference string) (string, map[s
 	}
 
 	files := map[string][]byte{}
-	for _, layer := range manifest.Layers {
+	// Locale layers are budgeted in title order so the languages that fit do
+	// not depend on the manifest's layer order.
+	layers := append([]ocispec.Descriptor(nil), manifest.Layers...)
+	sort.SliceStable(layers, func(i, j int) bool {
+		return layers[i].Annotations[AnnotationTitle] < layers[j].Annotations[AnnotationTitle]
+	})
+	var budget LocaleBudget
+	for _, layer := range layers {
 		title := layer.Annotations[AnnotationTitle]
 		if title == "" {
 			continue
 		}
+		if _, isLocale := LocaleTag(title); isLocale {
+			// A locale layer with another media type is ignored, not
+			// trusted. One over the size bound, or one that would exceed the
+			// bundle's total locale budget, is never read (memory cap); the
+			// marker records its language so the reconciler can report it.
+			if layer.MediaType != MediaTypeLocale {
+				continue
+			}
+			if layer.Size > MaxLocaleLayerSize || !budget.Take(layer.Size) {
+				files[title] = OversizedLocale
+				continue
+			}
+		}
 		blob, err := readBlob(ctx, r, layer)
 		if err != nil {
 			return "", nil, fmt.Errorf("read layer %s: %w", title, err)
diff --git a/operator/internal/oci/locale_budget_test.go b/operator/internal/oci/locale_budget_test.go
new file mode 100644
index 000000000..abc15a052
--- /dev/null
+++ b/operator/internal/oci/locale_budget_test.go
@@ -0,0 +1,55 @@
+package oci
+
+import (
+	"context"
+	"strings"
+	"testing"
+)
+
+func TestLocaleBudget_Take(t *testing.T) {
+	var b LocaleBudget
+	if !b.Take(MaxLocaleTotalSize - 10) {
+		t.Fatal("first take within the budget was refused")
+	}
+	if b.Take(11) {
+		t.Fatal("take over the budget was accepted")
+	}
+	if !b.Take(10) {
+		t.Fatal("a refused take must reserve nothing, so a smaller one still fits")
+	}
+	if b.Take(1) {
+		t.Fatal("budget is full; take was accepted")
+	}
+	var neg LocaleBudget
+	if neg.Take(-1) {
+		t.Fatal("negative size was accepted")
+	}
+}
+
+func TestClient_Pull_LocaleTotalBudget(t *testing.T) {
+	reg := newFakeRegistry(t)
+	repo := "gameplane/locale-budget"
+	// 800 KiB each: five fit in the 4 MiB budget, the sixth does not.
+	body := []byte(strings.Repeat("x", 800*1024))
+	layers := map[string]typedLayer{
+		LayerNameMetadata: {MediaTypeMetadata, []byte(fixtureModuleYAML)},
+		LayerNameTemplate: {MediaTypeTemplate, []byte(fixtureTemplateYAML)},
+	}
+	for _, tag := range []string{"aa", "bb", "cc", "dd", "ee", "ff"} {
+		layers["locales/"+tag+".json"] = typedLayer{MediaTypeLocale, body}
+	}
+	reg.pushTyped(repo, "1.0.0", layers)
+
+	c := New(nil, true)
+	_, files, err := c.Pull(context.Background(), reg.host()+"/"+repo, "1.0.0")
+	if err != nil {
+		t.Fatalf("Pull: %v", err)
+	}
+	locales, oversized := SplitLocaleLayers(files)
+	if len(locales) != 5 {
+		t.Errorf("read %d locale files, want 5", len(locales))
+	}
+	if len(oversized) != 1 || oversized[0] != "ff" {
+		t.Errorf("oversized = %v, want [ff]", oversized)
+	}
+}
diff --git a/operator/internal/oci/locale_test.go b/operator/internal/oci/locale_test.go
new file mode 100644
index 000000000..36a8a3a32
--- /dev/null
+++ b/operator/internal/oci/locale_test.go
@@ -0,0 +1,167 @@
+package oci
+
+import (
+	"context"
+	"encoding/json"
+	"strings"
+	"testing"
+
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+func TestLocaleTag(t *testing.T) {
+	cases := []struct {
+		title string
+		tag   string
+		ok    bool
+	}{
+		{"locales/fr.json", "fr", true},
+		{"locales/pt-BR.json", "pt-BR", true},
+		{"locales/zh-Hans-CN.json", "zh-Hans-CN", true},
+		{"locales/.json", "", false},
+		{"locales/fr.txt", "", false},
+		{"locales/a/b.json", "", false},
+		{"fr.json", "", false},
+		{"module.yaml", "", false},
+		{"", "", false},
+	}
+	for _, c := range cases {
+		tag, ok := LocaleTag(c.title)
+		if tag != c.tag || ok != c.ok {
+			t.Errorf("LocaleTag(%q) = %q, %v; want %q, %v", c.title, tag, ok, c.tag, c.ok)
+		}
+	}
+}
+
+func TestLocaleLayers(t *testing.T) {
+	got := LocaleLayers(map[string][]byte{
+		"module.yaml":        []byte("m"),
+		"locales/en.json":    []byte("en"),
+		"locales/fr.json":    []byte("fr"),
+		"locales/pt-BR.json": []byte("pt"),
+		"locales/x/y.json":   []byte("nested"),
+		"locales/notes.txt":  []byte("txt"),
+	})
+	if len(got) != 2 || string(got["fr"]) != "fr" || string(got["pt-BR"]) != "pt" {
+		t.Fatalf("LocaleLayers = %v", got)
+	}
+	if got := LocaleLayers(nil); len(got) != 0 {
+		t.Fatalf("LocaleLayers(nil) = %v", got)
+	}
+}
+
+type typedLayer struct {
+	mediaType string
+	data      []byte
+}
+
+// pushTyped pushes a bundle whose layers carry explicit media types, which
+// pushBundle does not support for locale layers.
+func (r *fakeRegistry) pushTyped(repo, tag string, layers map[string]typedLayer) string {
+	r.t.Helper()
+	empty := []byte(`{}`)
+	r.putBlob(empty)
+	manifest := ocispec.Manifest{
+		MediaType:    ocispec.MediaTypeImageManifest,
+		ArtifactType: ArtifactType,
+		Config: ocispec.Descriptor{
+			MediaType: MediaTypeConfig,
+			Digest:    digestFor(empty),
+			Size:      int64(len(empty)),
+		},
+	}
+	for name, l := range layers {
+		d := r.putBlob(l.data)
+		manifest.Layers = append(manifest.Layers, ocispec.Descriptor{
+			MediaType:   l.mediaType,
+			Digest:      digestFromString(d),
+			Size:        int64(len(l.data)),
+			Annotations: map[string]string{AnnotationTitle: name},
+		})
+	}
+	mb, err := json.Marshal(manifest)
+	if err != nil {
+		r.t.Fatalf("marshal manifest: %v", err)
+	}
+	return r.pushManifest(repo, tag, mb)
+}
+
+func TestClient_Pull_LocaleLayers(t *testing.T) {
+	reg := newFakeRegistry(t)
+	repo := "gameplane/locales"
+	big := []byte(strings.Repeat("x", MaxLocaleLayerSize+1))
+	reg.pushTyped(repo, "1.0.0", map[string]typedLayer{
+		LayerNameMetadata:      {MediaTypeMetadata, []byte(fixtureModuleYAML)},
+		LayerNameTemplate:      {MediaTypeTemplate, []byte(fixtureTemplateYAML)},
+		"locales/fr.json":      {MediaTypeLocale, []byte(`{"a":{"defaultMessage":"x"}}`)},
+		"locales/de.json":      {"application/octet-stream", []byte(`{}`)},
+		"locales/it.json":      {MediaTypeLocale, big},
+		"locales/pt-BR.json":   {MediaTypeLocale, []byte(`{}`)},
+		"locales/not-a-layer/": {MediaTypeLocale, []byte(`{}`)},
+	})
+
+	c := New(nil, true)
+	_, files, err := c.Pull(context.Background(), reg.host()+"/"+repo, "1.0.0")
+	if err != nil {
+		t.Fatalf("Pull: %v", err)
+	}
+	if _, ok := files["locales/fr.json"]; !ok {
+		t.Error("typed locale layer was not returned")
+	}
+	if _, ok := files["locales/pt-BR.json"]; !ok {
+		t.Error("pt-BR locale layer was not returned")
+	}
+	if _, ok := files["locales/de.json"]; ok {
+		t.Error("mistyped locale layer was returned")
+	}
+	if !IsOversizedLocale(files["locales/it.json"]) {
+		t.Errorf("over-size locale layer = %q, want the oversized marker", files["locales/it.json"])
+	}
+	locales, oversized := SplitLocaleLayers(files)
+	if len(locales) != 2 {
+		t.Errorf("SplitLocaleLayers locales = %d entries, want 2", len(locales))
+	}
+	if len(oversized) != 1 || oversized[0] != "it" {
+		t.Errorf("oversized = %v, want [it]", oversized)
+	}
+}
+
+func TestSplitLocaleLayers(t *testing.T) {
+	cases := []struct {
+		name      string
+		files     map[string][]byte
+		locales   []string
+		oversized []string
+	}{
+		{"nil", nil, nil, nil},
+		{"plain", map[string][]byte{"locales/fr.json": []byte("x")}, []string{"fr"}, nil},
+		{"oversized sorted", map[string][]byte{
+			"locales/fr.json": []byte("x"),
+			"locales/de.json": OversizedLocale,
+			"locales/ca.json": OversizedLocale,
+		}, []string{"fr"}, []string{"ca", "de"}},
+		{"en skipped", map[string][]byte{"locales/en.json": OversizedLocale}, nil, nil},
+		{"non-locale ignored", map[string][]byte{"module.yaml": OversizedLocale}, nil, nil},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			locales, oversized := SplitLocaleLayers(c.files)
+			if len(locales) != len(c.locales) {
+				t.Fatalf("locales = %v, want %v", locales, c.locales)
+			}
+			for _, tag := range c.locales {
+				if _, ok := locales[tag]; !ok {
+					t.Errorf("missing %s", tag)
+				}
+			}
+			if len(oversized) != len(c.oversized) {
+				t.Fatalf("oversized = %v, want %v", oversized, c.oversized)
+			}
+			for i := range oversized {
+				if oversized[i] != c.oversized[i] {
+					t.Errorf("oversized = %v, want %v", oversized, c.oversized)
+				}
+			}
+		})
+	}
+}
diff --git a/operator/specs.md b/operator/specs.md
index 52e45e7c0..15a2c9be8 100644
--- a/operator/specs.md
+++ b/operator/specs.md
@@ -11,7 +11,7 @@ The operator is a Kubernetes controller-runtime-based process that reconciles Ga
 ## Responsibilities
 
 - **GameServer lifecycle:** reconcile GameServer CRs into StatefulSets, Services, PVCs, and pod-injected agent sidecars; manage pod affinity, RCON/console integration, file I/O, and graceful stop sequences.
-- **Module installation:** pull OCI module bundles from remote or local sources, verify signatures (cosign), and materialize GameTemplate CRs; refresh source indexes periodically.
+- **Module installation:** pull OCI module bundles from remote or local sources, verify signatures (cosign), and materialize GameTemplate CRs; refresh source indexes periodically. Translation files (`locales/<tag>.json`) are carried by every module source (OCI layers, directory, git, HTTP archive, upload, `gp-module package` tarball) and validated against the ids derived from the module (`i18n/modlocale`); valid entries are written to the `<template>-locales` ConfigMap (owned by the GameTemplate, in the operator namespace) and problems surface as the GameTemplate `LocalesValid` condition (reasons `Valid`, `InvalidEntries`, `LocalesTooLarge`, `WriteFailed`) and Warning events, never as an install failure. A file over 900 KiB, or a language that would push the bundle's locale files past 4 MiB together (counted in file-name order), is not read but reported by language tag as `LocalesTooLarge`. Events fire only when the problem list changes (fingerprint annotation `gameplane.local/locales-problems`). The ConfigMap is rewritten on each apply, not recreated if deleted while the Module stays converged.
 - **Backup & restore:** coordinate application-level quiesce with agent, spawn restic backup/restore Jobs, track snapshot IDs, and enforce retention policies.
 - **Scheduled backups:** parse cron expressions, create Backup objects on schedule, apply retention rules (keep-daily, keep-hourly, etc.), and report schedule validity and retention status.
 - **Remote cluster health:** periodically probe Kubernetes clusters reachable via kubeconfig Secrets, report connectivity and API-server health.
@@ -72,7 +72,8 @@ operator/
 │   │   ├── restore_controller.go           Drives Restore → restic Job with GameServer suspend
 │   │   ├── restore_volumesnapshot.go       Snapshot recovery for restore strategy
 │   │   ├── modulesource_controller.go      Indexes module sources, refreshes catalog
-│   │   ├── module_controller.go            Pulls OCI bundle, verifies signature, creates GameTemplate
+│   │   ├── module_controller.go            Pulls OCI bundle, verifies signature, creates GameTemplate, publishes module translations
+│   │   ├── module_locales.go               Validates module translations, writes the <template>-locales ConfigMap, LocalesValid condition + events
 │   │   ├── cluster_controller.go           Health checks remote clusters via kubeconfig
 │   │   ├── networkcapture_controller.go    Drives NetworkCapture → sidecar injection + retention/expiry
 │   │   ├── agent_certs.go                  Generates per-GameServer agent mTLS certs
@@ -81,6 +82,7 @@ operator/
 │   │   ├── retention.go                    Backup retention logic (keep-daily, keep-hourly, etc.)
 │   │   ├── restic_summary.go               Parses restic JSON output from container logs
 │   │   ├── semver.go                       Semantic versioning helpers
+│   │   ├── gameserver_condition_args.go    conditionArgs derivation and localized-reason arguments (GameServer status)
 │   │   ├── helpers.go                      Utility functions shared across reconcilers
 │   │   └── *_envtest_test.go               Co-located integration tests (envtest tier)
 │   │
@@ -110,7 +112,7 @@ Nine CRD kinds under `gameplane.local/v1alpha1`:
 
 | Kind | File | Purpose |
 |------|------|---------|
-| **GameTemplate** | `gametemplate_types.go` | Reusable blueprint for a game server (image, ports, probes, RCON protocol, mod loaders, etc.). Cluster-wide catalog; instances are created via GameServer references. Status tracks in-use count. |
+| **GameTemplate** | `gametemplate_types.go` | Reusable blueprint for a game server (image, ports, probes, RCON protocol, mod loaders, etc.). Cluster-wide catalog; instances are created via GameServer references. Status tracks in-use count and the `LocalesValid` condition (module translations). |
 | **Module** | `module_types.go` | User request to pull and install a module (OCI bundle) from a ModuleSource. Creates a child GameTemplate on success; delete cascades to the template via owner reference. |
 | **ModuleSource** | `modulesource_types.go` | Registry of module bundles (OCI, git, HTTP, or local). Declares source location, refresh interval, optional credentials Secret, and optional cosign verification policy. Status lists available modules. |
 | **Cluster** | `cluster_types.go` | Metadata for a remote Kubernetes cluster (displayName, kubeconfig Secret ref). Cluster-scoped so multiple control planes can discover each other. Status tracks health (Unknown/Healthy/Unhealthy), lastCheckTime, conditions. |
@@ -205,6 +207,7 @@ Primary reconcilers register with the manager in `cmd/main.go` and handle CRD li
     - Precedence when several apply: `IgnoredForExposureMode` → `InvalidAddress` → `NoAddressManagerConfigured` → direct-conflict `AddressInUse` → event-derived failure → `ServiceNotReady` → `AssignmentPending` → `Assigned`.
   - **Endpoint population:** `endpointsFromService()` populates `GameServerEndpoint.pool` only when a pool request was actually translated (outcome == Assigned and Manager supports it); never claims a pool for the ClusterIP address shown while assignment is pending, for an ignored request, or for a cluster without an address manager.
   - **status.startedAt:** while the server is Running, `status.startedAt` follows the start time of the running game container, matched by container name (`gameContainerStartedAt` in `gameserver_status.go`). Uptime therefore resets when the game container restarts inside the same pod. When that time is unavailable, `startedAt` is set once to the current time and kept. Test: `TestGameContainerStartedAt` (`gameserver_status_test.go`).
+  - **conditionArgs:** `status.conditionArgs[<ConditionType>]` carries the values interpolated into the English `message` of the condition's current reason, recomputed on every `reconcileStatus` pass by `deriveConditionArgs` (`gameserver_condition_args.go`); `setPhase`, `setTunnelCredentialRefused` and `clearTunnelCredentialRefused` maintain their own entry. The `message` is unchanged. Translation ids are `condition.<type>.<reason>` (lower-cased) and are listed in `i18n/locales/en/app.json`.
   - **TunnelReady condition:** Reports tunnel pod readiness when `spec.networking.tunnel.enabled=true` (absent when disabled). Computed in `computeTunnelConditions` (`gameserver_status.go`) each pass reconcileStatus runs, with reasons `InvalidConfig`, `DeploymentNotReady`, `PortNotMapped` (frp, unmapped advertised ports), `NoCredentials` (tailscale/playit missing `credentialsSecretRef`), `UnknownProvider`, and `Ready`. **Credential ownership:** `reconcileTunnel` refuses to mount a `credentialsSecretRef` Secret that has no `ownerReference` matching the GameServer's name and UID (including a stale reference from a deleted same-name GameServer) (`isServerOwnedSecret`) — supported credential paths are the dashboard, the `PUT /servers/{name}:tunnel-credentials` API (which sets the ownerReference), or a manually-created Secret with an explicit ownerReference. A refused Secret is never mounted: `reconcileTunnel` still writes the tunnel Deployment, with no credential volume and zero replicas, so a tunnel already running with that Secret stops. It also writes `TunnelReady=False/TunnelCredentialRefused` (naming the Secret, never its data) directly from `reconcileTunnel` before `Reconcile` returns its error — this bypasses the normal `reconcileStatus` pass since Reconcile returns early on that error — The condition carries its own current `observedGeneration`, but `status.observedGeneration` is not advanced on a refused pass (the rest of status is not recomputed). Once the credential becomes acceptable (or the tunnel is no longer wanted), `reconcileTunnel` removes the refusal condition itself (`clearTunnelCredentialRefused`) before returning, so it does not linger if a later step (NetworkPolicy, Service, StatefulSet) fails; reconcileStatus then writes the real TunnelReady. The refusal message points at the dashboard/API, except when the refused Secret is the canonical `<server>-tunnel-auth` name, where the API answers 409 and the message says to fix the ownerReference or delete the Secret first.
 
 ### GameTemplateReconciler
@@ -363,6 +366,8 @@ Primary reconcilers register with the manager in `cmd/main.go` and handle CRD li
 - **restic_summary.go:** Parse restic container logs, extract final JSON summary (snapshot ID, duration, size).
 - **semver.go:** Semantic versioning utilities (compare version strings against gameplaneMinVersion).
 - **helpers.go:** Shared utilities (updateCondition, upsertCondition, phase transition helpers).
+- **gameserver_condition_args.go:** `deriveConditionArgs` rebuilds `status.conditionArgs` from the final GameServer conditions on every `reconcileStatus` pass (the values each reason's English message interpolates); `setConditionArgs` maintains the entries written out of band; `provisioningArgs` reads the pod's container states for CrashLoopBackOff and ContainerExited.
+- **hack/condition-ids (generator):** `go run ./hack/condition-ids -app ../i18n/locales/en/app.json` writes every `condition.<type>.<reason>` id from its table into the English reference (`make i18n-sync`); `-check` (run by `make check-i18n`) reports drift and exits 1. Its coverage guard parses the non-test controller sources with `go/parser` and fails when a reason literal they set has no table entry, or when a non-dynamic table reason is set nowhere; it reports the mismatch rather than editing the table. Rows marked dynamic (Backup `Pending`/`Running`, which come from the phase string) are exempt from the second check.
 
 ## External interface / contracts
 
diff --git a/specs/019-localization-language-packs/OPEN-DECISIONS.md b/specs/019-localization-language-packs/OPEN-DECISIONS.md
index b70960ef7..4b2740511 100644
--- a/specs/019-localization-language-packs/OPEN-DECISIONS.md
+++ b/specs/019-localization-language-packs/OPEN-DECISIONS.md
@@ -1,6 +1,6 @@
 # Open Decisions: App Localization & Community Language Packs
 
-All four decisions below were settled by valgul on 2026-10-10 and are recorded in spec.md (Clarifications, Session 2026-10-10).
+The first four decisions were settled by valgul on 2026-10-10 and are recorded in spec.md (Clarifications, Session 2026-10-10). The US6 module-translation rulings (OD-005 to OD-014) and the design placement rulings (OD-015 to OD-017) were settled on 2026-10-12 (Clarifications, Session 2026-10-12).
 
 ## OD-001: Which pilot language ships at launch — RESOLVED: French (valgul, 2026-10-10)
 
@@ -55,3 +55,93 @@ Options:
 Decision: per-destination language setting, defaulting to the instance default language.
 
 Affects: FR-028
+
+## US6 module-translation rulings
+
+Ten decisions on the module translations (user story 6), all settled 2026-10-12 by valgul.
+
+## OD-005: Namespace of the translations ConfigMap - RESOLVED: the operator namespace (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. The ConfigMap `<template>-locales` lives in the operator namespace, the namespace Gameplane runs in (`--module-namespace`). The GameTemplate is cluster-scoped, so the owner reference points at a cluster-scoped owner. The API reads the same namespace.
+
+Affects: FR-031, T087
+
+## OD-006: Where module id derivation lives - RESOLVED: `i18n/modlocale` (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. One shared package derives module ids for `gp-module`, `i18n-check --module` and the operator. The `i18n` module may depend on `gopkg.in/yaml.v3`.
+
+Affects: FR-031, T084
+
+## OD-007: Module id rule - RESOLVED: upper case and `~` allowed (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. Module ids get their own documented rule that allows upper case and `~` with reversible `~0`/`~1` escaping. Dashboard and server ids keep the strict lower-case regex.
+
+Settled 2026-10-12 by valgul: gp-module validate reports such names as error locale-id-invalid (scan of all 29 modules: 0 of 808 ids affected).
+
+Affects: FR-031, T084
+
+## OD-008: Meaning of `i18n-check --module` - RESOLVED: en.json must equal the derived ids (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. `en.json` must match the ids derived from the YAML (also when the YAML derives nothing); every translation is validated against the derived set.
+
+Affects: FR-031, T085, T090
+
+## OD-009: LocalesValid reporting - RESOLVED: full reporting (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. `LocalesValid=True` with reason `Valid` when fine; `False` with `LocalesTooLarge` before `InvalidEntries`; a new reason `WriteFailed` when the ConfigMap write fails.
+
+Settled 2026-10-12 by valgul: WriteFailed ranks first.
+
+Affects: FR-034, T087
+
+## OD-010: Oversized locale layers - RESOLVED: recorded by tag (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. An oversized locale file is never dropped silently at pull time. A hard memory cap stays on reading; the language tag is recorded as oversized, reaches the reconciler and shows as `LocalesTooLarge` naming the language in the condition message and the Warning event.
+
+Affects: FR-034, T086, T087
+
+## OD-011: Module sources that carry translations - RESOLVED: all (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. Directory, git, HTTP, upload and `gp-module package --output` tarball sources carry `locales/*.json` as well as OCI layers, with the same file names and validation. Scout note: the upload ConfigMap key is `locales.<tag>.json`.
+
+Affects: FR-031, T086, T087
+
+## OD-012: Locales endpoint edge cases - RESOLVED: `200 {}` and ICU strings (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. `GET /modules/{name}/locales/{tag}` with a malformed tag returns `200 {}`; values are the validated ICU message strings.
+
+Affects: FR-032, T088
+
+## OD-013: sourceHash on module translations - RESOLVED: yes (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. Module translations carry `sourceHash` like app packs; a changed English text shows a needs-review notice. Authoring: `gp-module i18n stamp` writes the hash and `gp-module validate` warns (`locale-needs-review`). i18n-check --module --stamp stays a usage error; gp-module i18n stamp is the only module stamping tool.
+
+Affects: FR-031, T085
+
+## OD-014: Warning event frequency - RESOLVED: only when the problem list changes (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. Warning events fire only when the problem list changes, tracked by a fingerprint annotation `gameplane.local/locales-problems` on the GameTemplate, not on every re-pull.
+
+Affects: FR-034, T087
+
+## Design placement rulings
+
+Three decisions on the design tasks (T043, T072), all settled 2026-10-12 by valgul.
+
+## OD-015: Where a sink's language is edited - RESOLVED: the Add sink form and each sink row (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. The design had no destination form, only the sink rows and an "Add sink" button. The Add sink form gets a Language select that defaults to "Instance default", and every existing sink row gets its own Language select, so the language can be changed without deleting the sink and entering its credentials again.
+
+Affects: FR-028, T072, T073
+
+## OD-016: Position of the Language card in personal settings - RESOLVED: first card (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. The Language card is the first card of the Theme & Appearance page, above Preset theme. The page title and subtitle stay unchanged.
+
+Affects: FR-001, T043, T044
+
+## OD-017: Position of the compact picker on the login and share pages - RESOLVED: top-right corner of the card (valgul, 2026-10-12)
+
+Settled 2026-10-12 by valgul. The compact picker sits inside the card, in its top-right corner, on every state of the login and share pages. It shows only the native names of the languages.
+
+Affects: FR-005, T043, T045
diff --git a/specs/019-localization-language-packs/contracts/check-tool.md b/specs/019-localization-language-packs/contracts/check-tool.md
index fe860576b..11bf3dc53 100644
--- a/specs/019-localization-language-packs/contracts/check-tool.md
+++ b/specs/019-localization-language-packs/contracts/check-tool.md
@@ -9,15 +9,18 @@ go run ./i18n/cmd/i18n-check [flags] <locales-dir>
   --reference en            reference tag (default en)
   --base <dir>              base-branch copy for before/after completeness
   --extracted <file>        formatjs extract output to compare with the reference (drift)
+  --registry <file>         API message registry JSON (from api/cmd/messages-export) for the two server flags
   --sync-server             write api/internal/messages registry into the reference
   --check-server            fail if the registry and the reference differ
   --used-ids <file>         ids referenced by code (from extract + Go registry) → unused report
   --manifest <out.json>     write languages.json
   --stamp                   write sourceHash for translated entries
-  --module <template.yaml>  module mode: ids derived from the template
+  --module <template.yaml>  module mode (see below)
   --summary <file>          GitHub job summary markdown
 ```
 
+Module mode reads `<template.yaml>` and the `module.yaml` beside it, derives the reference with `i18n/modlocale` (the same ids as `gp-module i18n extract` and the operator, following the module id rule in [module-locales.md](./module-locales.md) §1), requires `<locales-dir>/en.json` to equal the derived set (`extract-drift` for a missing or changed id, `unknown-id` for an extra id, also when the template derives nothing), and validates every other `<tag>.json` against the derived set. File names must be valid language tags (`malformed-pack` otherwise). Without a `module.yaml`, `module.*` ids are not derived, so an `en.json` containing them reports `unknown-id`. The app-only flags, including `--stamp`, remain invalid with `--module`; stamp module translations with `gp-module i18n stamp` (see [module-locales.md](./module-locales.md) §1).
+
 Exit 0 = pass, 1 = findings, 2 = usage/IO error.
 
 ## Findings (each names file, id and a plain-language problem — FR-015)
diff --git a/specs/019-localization-language-packs/contracts/module-locales.md b/specs/019-localization-language-packs/contracts/module-locales.md
index 7ab1bf16c..5c402ced2 100644
--- a/specs/019-localization-language-packs/contracts/module-locales.md
+++ b/specs/019-localization-language-packs/contracts/module-locales.md
@@ -1,6 +1,6 @@
 # Contract: Module Translations
 
-**Feature**: `019-localization-language-packs` | **Binding modules**: `gp-module/`, `modules/build.sh`, `operator/internal/oci`, `operator/internal/controller` (GameTemplate), `api/internal/handlers/modules.go` | **Status**: Binding
+**Feature**: `019-localization-language-packs` | **Binding modules**: `gp-module/`, `modules/build.sh`, `operator/internal/oci`, `operator/internal/modsrc`, `operator/internal/controller` (Module reconciler), `api/internal/handlers/modules.go`, `api/internal/handlers/module_upload.go` | **Status**: Binding
 
 ## 1. Ids (derived from module.yaml / template.yaml; generated by `gp-module i18n extract`)
 
@@ -17,20 +17,51 @@
 
 Ids use the YAML identifiers with a reversible escape (JSON Pointer style): `~` → `~0`, then `.` → `~1`. So `a.b` becomes `a~1b` and `a~b` becomes `a~0b`; unescaping applies `~1` → `.` then `~0` → `~`. Commands, regexes, env values and images are never translatable.
 
-## 2. Packaging
+**Module id rule.** A module id is one of the fixed prefixes `module`, `template`, `versions`, `config`, `actions`, `mods`, `metrics` followed by dot-separated segments of `[A-Za-z0-9_~-]`, where `~` appears only as the escapes `~0` and `~1`:
 
-- Each `locales/<tag>.json` is one OCI layer, media type `application/vnd.gameplane.module.locale.v1+json`, title annotation `locales/<tag>.json`. `en.json` is not pushed (the template is the default text).
-- Pushed by `modules/build.sh` and `gp-module package`; covered by the existing cosign manifest signature (FR-033). Bundles without locale layers stay valid.
+```text
+^(module|template|versions|config|actions|mods|metrics)(\.[A-Za-z0-9_~-]+)+$
+```
+
+Upper case is allowed because ids embed names from the YAML (for example `config.MAX_PLAYERS.displayName`). Dashboard and server ids keep the strict lower-case regex in [data-model.md](../data-model.md). The shared derivation and the rule live in `i18n/modlocale` (`Derive`, `ValidID`); `gp-module i18n extract`, `i18n-check --module` and the operator all use it. Open risk: a YAML identifier or enum value containing a space, `/`, `:` or `+` yields an id outside the character set; see OPEN-DECISIONS.md (OD-007).
+
+Module translations carry `sourceHash` like app packs: the first 12 hex characters of the SHA-256 of the English text, written by `gp-module i18n stamp`. A changed English text makes the entry `needs-review` (still shown; `gp-module validate` warns with rule `locale-needs-review`).
+
+## 2. Packaging (all module sources)
+
+Each `locales/<tag>.json` reaches the operator through every module source, with the same file names and the same validation. `en.json` is never shipped (the template is the default text).
+
+| Source | How a translation travels |
+|---|---|
+| OCI | one layer per file: media type `application/vnd.gameplane.module.locale.v1+json`, title annotation `locales/<tag>.json`; a layer over 900 KiB is recorded as oversized, not dropped |
+| directory, local, git, HTTP archive (tar.gz / zip) | the file `locales/<tag>.json` in the module directory |
+| upload | ConfigMap key `locales.<tag>.json` (a key cannot contain `/`); the API copies `locales/<tag>.json` from the uploaded archive and counts the bytes against the bundle limit |
+| `gp-module package --output` tar.gz | contains `locales/<tag>.json` (so it works as an HTTP or upload source) |
+
+Pushed to OCI by `modules/build.sh` and `gp-module package`. Cosign covers OCI layers through the manifest signature (FR-033); the other sources have no signature (existing behavior). Bundles without locale files stay valid.
 
 ## 3. Operator
 
-On GameTemplate install/upgrade: validate each locale layer with `i18n/pack` against ids extracted from the bundled template. Valid entries → ConfigMap `<template>-locales` (`data["<tag>.json"]`, owner ref → GameTemplate). Invalid entries dropped; condition `LocalesValid=False`, reason `InvalidEntries`, Warning event listing up to 20 `tag:id: problem` lines. Module install never fails because of locales (FR-034).
+The Module reconciler (the GameTemplate reconciler never sees the bundle) validates each locale file with `i18n/pack` against ids derived from the bundled `module.yaml` and `template.yaml` on install/upgrade. Valid entries go to ConfigMap `<template>-locales` (`data["<tag>.json"]`) in the operator namespace, the namespace Gameplane runs in (`--module-namespace`); the GameTemplate is cluster-scoped, so the owner reference points at a cluster-scoped owner. Invalid entries are dropped. Module install never fails because of locales (FR-034).
+
+Condition `LocalesValid`:
+
+| Reason | Status | When |
+|---|---|---|
+| `Valid` | True | every translation is valid; message "All module translations are valid." |
+| `InvalidEntries` | False | entries or whole files were dropped |
+| `LocalesTooLarge` | False | a language is over the size limit or the languages together exceed it |
+| `WriteFailed` | False | the ConfigMap could not be written; retried after a minute |
+
+Priority when several apply: `WriteFailed` > `LocalesTooLarge` > `InvalidEntries` > `Valid`.
+
+Size bounds: one file is read up to 900 KiB (a hard memory cap); a larger file reaches the reconciler as an "oversized" language tag, is never stored, and makes `LocalesTooLarge`. All locale files of one bundle together are read up to 4 MiB (`oci.MaxLocaleTotalSize`), counted in file-name order (OCI layers by title annotation, directories by file name, so `pt-BR.json` sorts before `pt.json`); a language that would push the running total over the budget is recorded as oversized like an oversized file and is not read, while a later, smaller language can still fit. This applies to the OCI and directory-based sources (directory, local, git, HTTP archive); uploads stay bounded by the 900 KiB bundle limit. The ConfigMap data for all languages together MUST stay ≤ 900 KiB (below the 1 MiB Kubernetes limit): languages are added in tag order until the next one would exceed the bound; the rest are left out. The language tags of both kinds appear in the condition message and in the Warning event, and those languages fall back to the template's default text.
 
-Size bound: the ConfigMap data for all languages together MUST stay ≤ 900 KiB (below the 1 MiB Kubernetes limit). Languages are added in tag order until the next one would exceed the bound; the rest are left out, the condition is `LocalesValid=False` with reason `LocalesTooLarge`, and a Warning event names the dropped languages. Dropped languages fall back to the template's default text.
+Events: Warning events `InvalidLocaleEntries` (up to 20 `tag:id: problem` lines, note capped at 1024 bytes), `LocalesTooLarge` and `LocalesWriteFailed` fire only when the problem list changes, tracked by the annotation `gameplane.local/locales-problems` (a fingerprint) on the GameTemplate, not on every re-pull. A failed write counts as one problem whatever its error text, so the one-minute retries do not repeat events; a failed delete of stale translations also reports `WriteFailed`.
 
 ## 4. API
 
-`GET /api/v1/modules/{name}/locales/{tag}` (mounted in the existing `/modules` route group, `api/internal/handlers/modules.go`) → `200 {"<id>": "<compiled message>"}`; resolution `tag` → base language → `{}`. Same RBAC as `GET /api/v1/modules/{name}`. `404` only when the module does not exist.
+`GET /api/v1/modules/{name}/locales/{tag}` (mounted in the existing `/modules` route group, `api/internal/handlers/modules.go`) → `200 {"<id>": "<ICU message string>"}`: the validated message text exactly as stored (the dashboard formats it; the API never compiles it). Resolution `tag` → base language → `{}`. A malformed or unknown tag, a module with no translations and a missing ConfigMap all return `200 {}`; `404` only when the module does not exist. Requires `modules:read`, the same RBAC as `GET /api/v1/modules/{name}`.
 
 ## 5. Dashboard
 
diff --git a/specs/019-localization-language-packs/contracts/pack-format.md b/specs/019-localization-language-packs/contracts/pack-format.md
index 9d1f9a89e..784ebdaa1 100644
--- a/specs/019-localization-language-packs/contracts/pack-format.md
+++ b/specs/019-localization-language-packs/contracts/pack-format.md
@@ -65,7 +65,7 @@ modules/<name>/locales/
 └── fr.json
 ```
 
-Same Format.JS JSON rules; ids per [module-locales.md](./module-locales.md). No `meta.json` (language metadata comes from the app pack).
+Same Format.JS JSON rules; ids per [module-locales.md](./module-locales.md). No `meta.json` (language metadata comes from the app pack). `sourceHash` works as in app packs (first 12 hex characters of the SHA-256 of the English text) and is written by `gp-module i18n stamp`.
 
 ## 4. Generated runtime artifacts (not committed)
 
diff --git a/specs/019-localization-language-packs/data-model.md b/specs/019-localization-language-packs/data-model.md
index 633e5dc74..8e15db6a0 100644
--- a/specs/019-localization-language-packs/data-model.md
+++ b/specs/019-localization-language-packs/data-model.md
@@ -29,7 +29,7 @@ Stored in `i18n/locales/<tag>/meta.json`. `en` is always listed (completeness 10
 
 | Field | Type | Rules |
 |---|---|---|
-| `id` | string | `^[a-z][a-z0-9_]*(\.[a-z0-9_-]+)+$`; namespace prefix `web.`, `server.`, `condition.`, `notify.`, `audit.` (app) or the module id scheme in [module-locales.md](./contracts/module-locales.md); stable once shipped |
+| `id` | string | App ids: `^[a-z][a-z0-9_]*(\.[a-z0-9_-]+)+$` with namespace prefix `web.`, `server.`, `condition.`, `notify.`, `audit.`. Module ids: the module id rule in [module-locales.md](./contracts/module-locales.md) §1 (upper case, digits, `_`, `-`, `~0`/`~1` escapes). Stable once shipped |
 | `defaultMessage` | ICU MessageFormat | parses; only designated rich-text tags (`<b>`, `<link>`) |
 | `description` | string | required (translator note: where shown, placeholder meaning, length limit) |
 | placeholders | derived | set of argument names (incl. inside `plural`/`select`) |
diff --git a/specs/019-localization-language-packs/spec.md b/specs/019-localization-language-packs/spec.md
index 06bcfd74c..c36878daf 100644
--- a/specs/019-localization-language-packs/spec.md
+++ b/specs/019-localization-language-packs/spec.md
@@ -281,6 +281,15 @@ Decided by valgul; recorded as settled in OPEN-DECISIONS.md.
 - **Q7 (Notification language, OD-004)**: Per destination or instance-wide only?
   - **Decision**: Per notification destination, defaulting to the instance default language.
 
+### Session 2026-10-12
+
+Decided by valgul; recorded as settled in OPEN-DECISIONS.md (OD-005 to OD-017).
+
+- **Q8 (Module translations, US6)**: Where do they live and how are they reported?
+  - **Decision**: ConfigMap in the operator namespace; ids derived in `i18n/modlocale`; module id rule allows upper case and `~0`/`~1` escapes; `i18n-check --module` requires `en.json` to equal the derived ids; `LocalesValid` reports Valid, InvalidEntries, LocalesTooLarge and WriteFailed, with oversized files named by language; every module source (OCI, directory, git, HTTP, upload, tarball) carries `locales/*.json`; the locales endpoint returns `200 {}` for a malformed tag with ICU message strings; module translations carry `sourceHash`; Warning events fire only when the problem list changes.
+- **Q9 (Design placement, OD-015 to OD-017)**: Where do the language controls sit?
+  - **Decision**: A sink's language is edited in the Add sink form and on each sink row; the Language card is the first card of the personal settings page; the compact picker sits in the top-right corner of the card on the login and share pages.
+
 Existence check 2026-09-23: Confirmed no localization exists in the dashboard, server, modules, website, design source, specifications, issues or pull requests.
 
 ## Assumptions
diff --git a/specs/019-localization-language-packs/tasks.md b/specs/019-localization-language-packs/tasks.md
index bed341c49..af8890080 100644
--- a/specs/019-localization-language-packs/tasks.md
+++ b/specs/019-localization-language-packs/tasks.md
@@ -23,12 +23,12 @@ description: "Task list for 019 App Localization & Community Language Packs"
 
 **Purpose**: Create the shared `i18n/` Go module and add dashboard dependencies (plan.md "Source Code", research R1, R2).
 
-- [ ] T001 Create Go module `i18n/` (`i18n/go.mod`, module path `github.com/GameplanePanel/gameplane/i18n`, go 1.26.0, dependency `golang.org/x/text` only) and add `./i18n` to `go.work`
-- [ ] T002 Add `i18n` to `GO_MODULES` in `Makefile` and create `i18n/.testcoverage.yml` with a 90% threshold (same tier as `telemetryschema`); add `i18n 90` to the coverage list in `CLAUDE.md` and the repository map entry `i18n/  shared language packs, ICU formatter, pack validator, i18n-check`
-- [ ] T003 [P] Create `i18n/specs.md` describing responsibilities, pack format (link `specs/019-localization-language-packs/contracts/pack-format.md`), consumers (web, api, operator, gp-module, module repo CI) and invariants
-- [ ] T004 [P] Create the English reference skeleton `i18n/locales/en/app.json` (`{}`) and `i18n/locales/en/meta.json` (`tag en`, `nativeName English`, `englishName English`, `direction ltr`) per contracts/pack-format.md §1
-- [ ] T005 [P] Add `react-intl` (dependency) and `@formatjs/cli`, `eslint-plugin-formatjs` (devDependencies) to `web/package.json` and regenerate `web/package-lock.json` with `npm install` (no `--legacy-peer-deps`)
-- [ ] T006 [P] Add `COPY i18n/ ./i18n/` to `api/Dockerfile` and `operator/Dockerfile` (and `gp-module` image if present) before the Go build, and `COPY i18n/locales ../i18n/locales` to `web/Dockerfile` before `npm run build`
+- [X] T001 Create Go module `i18n/` (`i18n/go.mod`, module path `github.com/GameplanePanel/gameplane/i18n`, go 1.26.0, dependency `golang.org/x/text` only) and add `./i18n` to `go.work`
+- [X] T002 Add `i18n` to `GO_MODULES` in `Makefile` and create `i18n/.testcoverage.yml` with a 90% threshold (same tier as `telemetryschema`); add `i18n 90` to the coverage list in `CLAUDE.md` and the repository map entry `i18n/  shared language packs, ICU formatter, pack validator, i18n-check`
+- [X] T003 [P] Create `i18n/specs.md` describing responsibilities, pack format (link `specs/019-localization-language-packs/contracts/pack-format.md`), consumers (web, api, operator, gp-module, module repo CI) and invariants
+- [X] T004 [P] Create the English reference skeleton `i18n/locales/en/app.json` (`{}`) and `i18n/locales/en/meta.json` (`tag en`, `nativeName English`, `englishName English`, `direction ltr`) per contracts/pack-format.md §1
+- [X] T005 [P] Add `react-intl` (dependency) and `@formatjs/cli`, `eslint-plugin-formatjs` (devDependencies) to `web/package.json` and regenerate `web/package-lock.json` with `npm install` (no `--legacy-peer-deps`)
+- [X] T006 [P] Add `COPY i18n/ ./i18n/` to `api/Dockerfile` and `operator/Dockerfile` (and `gp-module` image if present) before the Go build, and `COPY i18n/locales ../i18n/locales` to `web/Dockerfile` before `npm run build`
 
 ---
 
@@ -40,40 +40,40 @@ description: "Task list for 019 App Localization & Community Language Packs"
 
 ### `i18n/` library and checker
 
-- [ ] T007 [P] Implement ICU subset parser in `i18n/icu/parse.go`: literals, `{arg}`, `{arg, number|date|time[, style]}`, `{arg, plural, =n {…} one {…} … other {…}}` with `#`, `{arg, select, … other {…}}`, apostrophe escaping, rich tags `<b>…</b>`/`<link>…</link>`; return AST + error with offset
-- [ ] T008 [P] Implement `i18n/icu/placeholders.go` returning the set of argument names (recursing into plural/select branches) and the set of rich tags used
-- [ ] T009 Implement `i18n/icu/format.go` formatting an AST with `map[string]any` args and a `language.Tag`, using `golang.org/x/text/feature/plural` for CLDR categories; unknown args render as `{name}` and never panic
-- [ ] T010 [P] Unit tests `i18n/icu/parse_test.go`, `placeholders_test.go`, `format_test.go` covering French/Polish/Arabic plural categories, reordering, escaping and malformed input
-- [ ] T011 Implement `i18n/pack/pack.go`: load Format.JS JSON (`id → {defaultMessage, description?, sourceHash?}`) and `meta.json` with unknown-key rejection; types `Pack`, `Meta`, `Entry`; `ListingThreshold = 80`
-- [ ] T012 Implement `i18n/pack/validate.go` producing findings with codes `malformed-pack`, `invalid-meta`, `icu-syntax`, `missing-placeholder`, `extra-placeholder`, `markup`, `unknown-id`, `missing-description`, `needs-review` exactly as contracts/check-tool.md; each finding names file, id and a plain-language problem (FR-015)
-- [ ] T013 Implement `i18n/pack/completeness.go` (per-entry status translated / needs-review / invalid / missing per data-model.md; completeness = (translated + needs-review) ÷ reference; `Listed()` = completeness ≥ ListingThreshold && direction ltr && tag != `en-XA`) and `sourceHash` (first 12 hex of SHA-256 of the English message)
-- [ ] T014 [P] Unit tests `i18n/pack/pack_test.go`, `validate_test.go`, `completeness_test.go`
-- [ ] T015 Create seeded defective fixtures `i18n/testdata/defective/<code>/` (one directory per error code in contracts/check-tool.md, each with a minimal `en/app.json`, `xx/app.json`, `xx/meta.json`; the `extract-drift`, `server-drift` and `unused-id` fixtures also carry `extracted.json`, `registry.json` or `used-ids.txt` plus an `args` file with the flags to pass, per contracts/check-tool.md) and `i18n/pack/fixtures_test.go` asserting each fixture yields exactly its code (SC-007)
-- [ ] T016 Implement `i18n/catalog/catalog.go` with `//go:embed locales/*/*.json`, `Tags()`, `Listed()` (app completeness ≥ 80, ltr, not `en-XA`, same rule as `pack.Listed`), `Lookup(tag language.Tag, id string, args map[string]any) (string, bool)` resolving regional → base → `en`, and dropping invalid translations at load (English shown instead)
-- [ ] T017 [P] Unit tests `i18n/catalog/catalog_test.go` (fallback chain, invalid-entry drop, missing id)
-- [ ] T018 Implement CLI `i18n/cmd/i18n-check/main.go` with every flag in contracts/check-tool.md (`--reference`, `--base`, `--extracted`, `--sync-server`, `--check-server`, `--used-ids`, `--manifest`, `--stamp`, `--module`, `--summary`), exit codes 0/1/2, and a markdown completeness table (tag, base → head, listed)
-- [ ] T019 [P] Unit tests `i18n/cmd/i18n-check/main_test.go` (flag parsing, manifest output shape from contracts/pack-format.md §4, summary before/after)
+- [X] T007 [P] Implement ICU subset parser in `i18n/icu/parse.go`: literals, `{arg}`, `{arg, number|date|time[, style]}`, `{arg, plural, =n {…} one {…} … other {…}}` with `#`, `{arg, select, … other {…}}`, apostrophe escaping, rich tags `<b>…</b>`/`<link>…</link>`; return AST + error with offset
+- [X] T008 [P] Implement `i18n/icu/placeholders.go` returning the set of argument names (recursing into plural/select branches) and the set of rich tags used
+- [X] T009 Implement `i18n/icu/format.go` formatting an AST with `map[string]any` args and a `language.Tag`, using `golang.org/x/text/feature/plural` for CLDR categories; unknown args render as `{name}` and never panic
+- [X] T010 [P] Unit tests `i18n/icu/parse_test.go`, `placeholders_test.go`, `format_test.go` covering French/Polish/Arabic plural categories, reordering, escaping and malformed input
+- [X] T011 Implement `i18n/pack/pack.go`: load Format.JS JSON (`id → {defaultMessage, description?, sourceHash?}`) and `meta.json` with unknown-key rejection; types `Pack`, `Meta`, `Entry`; `ListingThreshold = 80`
+- [X] T012 Implement `i18n/pack/validate.go` producing findings with codes `malformed-pack`, `invalid-meta`, `icu-syntax`, `missing-placeholder`, `extra-placeholder`, `markup`, `unknown-id`, `missing-description`, `needs-review` exactly as contracts/check-tool.md; each finding names file, id and a plain-language problem (FR-015)
+- [X] T013 Implement `i18n/pack/completeness.go` (per-entry status translated / needs-review / invalid / missing per data-model.md; completeness = (translated + needs-review) ÷ reference; `Listed()` = completeness ≥ ListingThreshold && direction ltr && tag != `en-XA`) and `sourceHash` (first 12 hex of SHA-256 of the English message)
+- [X] T014 [P] Unit tests `i18n/pack/pack_test.go`, `validate_test.go`, `completeness_test.go`
+- [X] T015 Create seeded defective fixtures `i18n/testdata/defective/<code>/` (one directory per error code in contracts/check-tool.md, each with a minimal `en/app.json`, `xx/app.json`, `xx/meta.json`; the `extract-drift`, `server-drift` and `unused-id` fixtures also carry `extracted.json`, `registry.json` or `used-ids.txt` plus an `args` file with the flags to pass, per contracts/check-tool.md) and `i18n/pack/fixtures_test.go` asserting each fixture yields exactly its code (SC-007)
+- [X] T016 Implement `i18n/catalog/catalog.go` with `//go:embed locales/*/*.json`, `Tags()`, `Listed()` (app completeness ≥ 80, ltr, not `en-XA`, same rule as `pack.Listed`), `Lookup(tag language.Tag, id string, args map[string]any) (string, bool)` resolving regional → base → `en`, and dropping invalid translations at load (English shown instead). *Done note: the `//go:embed` lives in the root package `i18n` (`i18n/embed.go`, `i18n.Locales`) because embed paths cannot use `..`; `catalog` loads from it.*
+- [X] T017 [P] Unit tests `i18n/catalog/catalog_test.go` (fallback chain, invalid-entry drop, missing id)
+- [X] T018 Implement CLI `i18n/cmd/i18n-check/main.go` with every flag in contracts/check-tool.md (`--reference`, `--base`, `--extracted`, `--sync-server`, `--check-server`, `--used-ids`, `--manifest`, `--stamp`, `--module`, `--summary`), exit codes 0/1/2, and a markdown completeness table (tag, base → head, listed). *Done note: `--registry <file>` added for the two server flags (contracts/check-tool.md updated); `--module` validates the flat `en.json` + `<tag>.json` layout now, and the template-derived id check plugs in with T084.*
+- [X] T019 [P] Unit tests `i18n/cmd/i18n-check/main_test.go` (flag parsing, manifest output shape from contracts/pack-format.md §4, summary before/after)
 
 ### API server-message plumbing (contract server-messages.md)
 
-- [ ] T020 Create registry `api/internal/messages/messages.go` (`type ID string`, `Entry{ID, English, Description}`, `New(id, args) *httperr.Message`, `All() []Entry`) seeded with the ids for every sentinel in `api/internal/httperr/httperr.go` `classify` (`server.namespace_forbidden`, `server.cluster_forbidden`, `server.not_found`, `server.already_exists`, `server.conflict_retry`, `server.forbidden`, `server.unauthorized`, `server.invalid`, `server.bad_request`, `server.empty_body`, `server.internal`, `server.remote_cluster_not_implemented`) plus `server.generic.<status>` for 400/401/403/404/409/413/422/429/500/501/502/503 and `server.auth.invalid_credentials`; English text byte-identical to today's strings
-- [ ] T021 Extend `api/internal/httperr/httperr.go`: `Message{ID, Args, Status, English}` implementing `error`; `WriteMessage`; negotiation helper that parses comma-separated `Accept` media ranges and `q` values (RFC 9110) and selects problem details only when `application/problem+json` is listed explicitly with q > 0 (wildcards and `q=0` never select it) → RFC 9457 body with `type`, `status`, `title`, `detail`, `messageId`, `args`; otherwise unchanged `http.Error` text/plain); `Write`/`WriteCode`/`classify` map sentinels to ids and honour `errors.As(*Message)`; `detail` omits the trailing newline of the plain-text body; 5xx `detail` stays status text
-- [ ] T022 [P] Unit tests `api/internal/httperr/httperr_test.go` additions: plain-text body byte-identical with and without the change for every classify branch (SC-010); problem body fields; `server.generic.*` for unmapped errors; 5xx never leaks error text; `Accept: application/problem+json;q=0` and `*/*` get text/plain
-- [ ] T023 Wire `i18n-check --sync-server` to the registry: add `api/internal/messages/export.go` (JSON dump of `All()`), a Makefile target `i18n-sync` (runs the export then `i18n-check --sync-server` into `i18n/locales/en/app.json`), and commit the resulting `server.*` entries
-- [ ] T024 Add `web/src/lib/api.ts` changes: always send `Accept: application/json, application/problem+json`; `APIError` gains `messageId?: string` and `args?: Record<string, string | number>` parsed from problem bodies; `message` keeps using `detail` so existing callers are unchanged; tests in `web/src/lib/api.test.ts`
+- [X] T020 Create registry `api/internal/messages/messages.go` (`type ID string`, `Entry{ID, English, Description}`, `New(id, args) *httperr.Message`, `All() []Entry`) seeded with the ids for every sentinel in `api/internal/httperr/httperr.go` `classify` (`server.namespace_forbidden`, `server.cluster_forbidden`, `server.not_found`, `server.already_exists`, `server.conflict_retry`, `server.forbidden`, `server.unauthorized`, `server.invalid`, `server.bad_request`, `server.empty_body`, `server.internal`, `server.remote_cluster_not_implemented`) plus `server.generic.<status>` for 400/401/403/404/409/413/422/429/500/501/502/503 and `server.auth.invalid_credentials`; English text byte-identical to today's strings
+- [X] T021 Extend `api/internal/httperr/httperr.go`: `Message{ID, Args, Status, English}` implementing `error`; `WriteMessage`; negotiation helper that parses comma-separated `Accept` media ranges and `q` values (RFC 9110) and selects problem details only when `application/problem+json` is listed explicitly with q > 0 (wildcards and `q=0` never select it) → RFC 9457 body with `type`, `status`, `title`, `detail`, `messageId`, `args`; otherwise unchanged `http.Error` text/plain); `Write`/`WriteCode`/`classify` map sentinels to ids and honour `errors.As(*Message)`; `detail` omits the trailing newline of the plain-text body; 5xx `detail` stays status text
+- [X] T022 [P] Unit tests `api/internal/httperr/httperr_test.go` additions: plain-text body byte-identical with and without the change for every classify branch (SC-010); problem body fields; `server.generic.*` for unmapped errors; 5xx never leaks error text; `Accept: application/problem+json;q=0` and `*/*` get text/plain
+- [X] T023 Wire `i18n-check --sync-server` to the registry: add `api/internal/messages/export.go` (JSON dump of `All()`), a Makefile target `i18n-sync` (runs the export then `i18n-check --sync-server` into `i18n/locales/en/app.json`), and commit the resulting `server.*` entries
+- [X] T024 Add `web/src/lib/api.ts` changes: always send `Accept: application/json, application/problem+json`; `APIError` gains `messageId?: string` and `args?: Record<string, string | number>` parsed from problem bodies; `message` keeps using `detail` so existing callers are unchanged; tests in `web/src/lib/api.test.ts`
 
 ### Dashboard i18n runtime (research R1, R5, R7)
 
-- [ ] T025 Add Vite alias `@i18n` → `../i18n/locales` and a build step in `web/vite.config.ts` (and `web/package.json` scripts `i18n:extract`, `i18n:compile`, `i18n:manifest`) that runs `formatjs extract 'src/**/*.{ts,tsx}' --format simple`-compatible output with descriptions, `formatjs compile --ast` per language into `web/src/generated/i18n/<tag>.json`, and `i18n-check --manifest web/src/generated/i18n/languages.json`; add `web/src/generated/` to `web/.gitignore`
-- [ ] T026 Create `web/src/lib/i18n/resolve.ts` implementing FR-004 order (user choice → browser choice → `navigator.languages` regional→base → instance default → `en`) over the listed languages from `languages.json`; unit tests `web/src/lib/i18n/resolve.test.ts`
-- [ ] T027 Create `web/src/lib/i18n/storage.ts` for `localStorage['gameplane-language']` `{choice, applied}` with try/catch around every access; tests `storage.test.ts`
-- [ ] T028 Create `web/src/lib/i18n/I18nProvider.tsx`: lazy-load compiled catalog chunk, wrap `react-intl` `IntlProvider` (`defaultLocale en`, `onError` logs missing ids in dev only, never renders ids) and `@react-aria/i18n` `I18nProvider`, update `document.documentElement.lang`/`dir` on change, switch without unmounting children (FR-002, FR-009); tests `I18nProvider.test.tsx` (switch keeps form state, fallback to English per message, no raw ids — FR-008)
-- [ ] T029 Add the synchronous boot snippet to `web/index.html` that reads `gameplane-language.applied` and sets `<html lang dir>` before React mounts (same pattern as the done_016 theme boot script); test in `web/src/__tests__/i18nBoot.test.ts`
-- [ ] T030 Mount the provider in the app root (`web/src/main.tsx` / `web/src/router/tree.tsx` root route) so it wraps every route including `/login` and `/share/*`
-- [ ] T031 Create formatting helpers `web/src/lib/i18n/format.ts` (`useFormat()` returning date, time, number, relative time, duration and list formatters bound to the active locale, FR-006) and replace hard-coded `en-US`/`toLocale*` calls in `web/src/components/ui/NotificationsPanel.tsx`, `web/src/components/registry-browser.tsx`, `web/src/components/CaptureWidget.tsx`, `web/src/routes/tabs/settings/ShareLinks.tsx`, `web/src/routes/tabs/settings/NetworkCapture.tsx`, `web/src/routes/tabs/Logs.tsx`, `web/src/routes/ThemeSettings.tsx`, `web/src/routes/AdminSettings.tsx`; tests `format.test.ts`
-- [ ] T032 Create `web/src/lib/i18n/serverMessage.ts` (`useServerMessage(err)` → translated text for `APIError.messageId` with args, appending `detail` for `server.generic.*` ids, else `detail`/`message`) and use it in `web/src/lib/errors.ts`; tests `serverMessage.test.ts`
-- [ ] T033 Add `eslint-plugin-formatjs` to `web/eslint.config.js` with `formatjs/enforce-description`, `formatjs/enforce-placeholders`, `formatjs/no-literal-string-in-jsx` (including `aria-label`, `title`, `placeholder`, `alt` props) as errors, scoped through a `MIGRATED_I18N_PATHS` files list that starts with `src/lib/i18n/**` and grows with each migration task (FR-022)
-- [ ] T034 Add CI job `i18n` in `.github/workflows/ci.yaml`: run `npm run i18n:extract` and `i18n-check --extracted … --check-server --used-ids … --base <base checkout>/i18n/locales --summary $GITHUB_STEP_SUMMARY i18n/locales`; include `i18n` in `make lint` (Makefile target `check-i18n`)
+- [X] T025 Add Vite alias `@i18n` → `../i18n/locales` and a build step in `web/vite.config.ts` (and `web/package.json` scripts `i18n:extract`, `i18n:compile`, `i18n:manifest`) that runs `formatjs extract 'src/**/*.{ts,tsx}' --format simple`-compatible output with descriptions, `formatjs compile --ast` per language into `web/src/generated/i18n/<tag>.json`, and `i18n-check --manifest web/src/generated/i18n/languages.json`; add `web/src/generated/` to `web/.gitignore`
+- [X] T026 Create `web/src/lib/i18n/resolve.ts` implementing FR-004 order (user choice → browser choice → `navigator.languages` regional→base → instance default → `en`) over the listed languages from `languages.json`; unit tests `web/src/lib/i18n/resolve.test.ts`
+- [X] T027 Create `web/src/lib/i18n/storage.ts` for `localStorage['gameplane-language']` `{choice, applied}` with try/catch around every access; tests `storage.test.ts`
+- [X] T028 Create `web/src/lib/i18n/I18nProvider.tsx`: lazy-load compiled catalog chunk, wrap `react-intl` `IntlProvider` (`defaultLocale en`, `onError` logs missing ids in dev only, never renders ids) and `@react-aria/i18n` `I18nProvider`, update `document.documentElement.lang`/`dir` on change, switch without unmounting children (FR-002, FR-009); tests `I18nProvider.test.tsx` (switch keeps form state, fallback to English per message, no raw ids — FR-008)
+- [X] T029 Add the synchronous boot snippet to `web/index.html` that reads `gameplane-language.applied` and sets `<html lang dir>` before React mounts (same pattern as the done_016 theme boot script); test in `web/src/__tests__/i18nBoot.test.ts`
+- [X] T030 Mount the provider in the app root (`web/src/main.tsx` / `web/src/router/tree.tsx` root route) so it wraps every route including `/login` and `/share/*`
+- [X] T031 Create formatting helpers `web/src/lib/i18n/format.ts` (`useFormat()` returning date, time, number, relative time, duration and list formatters bound to the active locale, FR-006) and replace hard-coded `en-US`/`toLocale*` calls in `web/src/components/ui/NotificationsPanel.tsx`, `web/src/components/registry-browser.tsx`, `web/src/components/CaptureWidget.tsx`, `web/src/routes/tabs/settings/ShareLinks.tsx`, `web/src/routes/tabs/settings/NetworkCapture.tsx`, `web/src/routes/tabs/Logs.tsx`, `web/src/routes/ThemeSettings.tsx`, `web/src/routes/AdminSettings.tsx`; tests `format.test.ts`
+- [X] T032 Create `web/src/lib/i18n/serverMessage.ts` (`useServerMessage(err)` → translated text for `APIError.messageId` with args, appending `detail` for `server.generic.*` ids, else `detail`/`message`) and use it in `web/src/lib/errors.ts`; tests `serverMessage.test.ts`
+- [X] T033 Add `eslint-plugin-formatjs` to `web/eslint.config.js` with `formatjs/enforce-description`, `formatjs/enforce-placeholders`, `formatjs/no-literal-string-in-jsx` (including `aria-label`, `title`, `placeholder`, `alt` props) as errors, scoped through a `MIGRATED_I18N_PATHS` files list that starts with `src/lib/i18n/**` and grows with each migration task (FR-022)
+- [X] T034 Add CI job `i18n` in `.github/workflows/ci.yaml`: run `npm run i18n:extract` and `i18n-check --extracted … --check-server --used-ids … --base <base checkout>/i18n/locales --summary $GITHUB_STEP_SUMMARY i18n/locales`; include `i18n` in `make lint` (Makefile target `check-i18n`)
 
 **Checkpoint**: Foundation ready. English-only catalog renders the dashboard unchanged; API plain-text bodies unchanged.
 
@@ -88,21 +88,21 @@ description: "Task list for 019 App Localization & Community Language Packs"
 ### Tests for User Story 1
 
 - [ ] T035 [P] [US1] Go API E2E `test/e2e/i18n_language_pref_e2e_test.go`: `PUT /api/v1/users/me/language` `fr` → `GET /users/me/preferences` returns `language: "fr"`; `null` clears; unknown tag → 400 with `server.i18n.unknown_language` problem body; register in `test/e2e/buckets.sh` (bucket `api-auth`, respect its login budget)
-- [ ] T036 [P] [US1] Go API E2E `test/e2e/i18n_auth_locale_e2e_test.go`: unauthenticated `GET /auth/locale` returns exactly `{"defaultLanguage": …}` and no other keys (rule 3); register in `test/e2e/buckets.sh`
+- [X] T036 [P] [US1] Go API E2E `test/e2e/i18n_auth_locale_e2e_test.go`: unauthenticated `GET /auth/locale` returns exactly `{"defaultLanguage": …}` and no other keys (rule 3); register in `test/e2e/buckets.sh`
 - [ ] T037 [P] [US1] Playwright `web/e2e/specs/live/i18n.spec.ts`: switch to French in personal settings with create-server dialog open and a typed name (kept, no reload, `<html lang="fr">`), reload and second browser context keep French with no English flash, login and share pages offer a picker remembered per browser, 0%-fixture language shows English everywhere (SC-008)
 
 ### Implementation for User Story 1
 
-- [ ] T038 [P] [US1] Migration `api/internal/db/migrations/common/016_user_language.sql`: `ALTER TABLE user_preferences ADD COLUMN language TEXT;` (portable, per `api/internal/db/migrations/README.md`)
-- [ ] T039 [US1] Add `Language *string` to `UserPreferences` and `SetLanguage(ctx, userID, *string)` (upsert keeping other columns / defaults) in `api/internal/db/preferences.go`; tests in `api/internal/db/preferences_test.go`
-- [ ] T040 [US1] Add `PUT /me/language` and `language` in `GET /me/preferences` in `api/internal/handlers/users.go` per contracts/i18n-api.md §1 (validate against `i18n/catalog.Listed()`, the same predicate as the picker; unknown or unlisted tag → `server.i18n.unknown_language`; handler test covers a shipped-but-unlisted tag); register the new message id in `api/internal/messages/messages.go`; handler tests `api/internal/handlers/users_language_test.go`
-- [ ] T041 [US1] Add `GET /auth/locale` in `api/internal/handlers/auth_providers.go`, mounted in the `/auth` route group of `api/cmd/main.go`, returning only `defaultLanguage` from config section `i18n` (absent → `en`); tests in `api/internal/handlers/auth_providers_test.go`
-- [ ] T042 [US1] Add `Users.setLanguage` and `Auth.locale` client methods in `web/src/lib/endpoints.ts`, `language` on the preferences type in `web/src/types.ts`; hydrate the user's language in `useMe()` so the shell renders only after it is known (US1 AS2)
-- [ ] T043 [US1] DESIGN (local machine, Pencil MCP): add to `design.pen` a Language section in personal settings (native names + completeness, current choice), a compact language picker for `/login` and `/share/*` (no internal info), and a mobile variant; export touched nodes to `assets/design-export/json/<id>.json` and `assets/design-export/screenshots/<id>.png` (design-export skill)
+- [X] T038 [P] [US1] Migration `api/internal/db/migrations/common/016_user_language.sql`: `ALTER TABLE user_preferences ADD COLUMN language TEXT;` (portable, per `api/internal/db/migrations/README.md`)
+- [X] T039 [US1] Add `Language *string` to `UserPreferences` and `SetLanguage(ctx, userID, *string)` (upsert keeping other columns / defaults) in `api/internal/db/preferences.go`; tests in `api/internal/db/preferences_test.go`
+- [X] T040 [US1] Add `PUT /me/language` and `language` in `GET /me/preferences` in `api/internal/handlers/users.go` per contracts/i18n-api.md §1 (validate against `i18n/catalog.Listed()`, the same predicate as the picker; unknown or unlisted tag → `server.i18n.unknown_language`; handler test covers a shipped-but-unlisted tag); register the new message id in `api/internal/messages/messages.go`; handler tests `api/internal/handlers/users_language_test.go`
+- [X] T041 [US1] Add `GET /auth/locale` in `api/internal/handlers/auth_providers.go`, mounted in the `/auth` route group of `api/cmd/main.go`, returning only `defaultLanguage` from config section `i18n` (absent → `en`); tests in `api/internal/handlers/auth_providers_test.go`
+- [X] T042 [US1] Add `Users.setLanguage` and `Auth.locale` client methods in `web/src/lib/endpoints.ts`, `language` on the preferences type in `web/src/types.ts`; hydrate the user's language in `useMe()` so the shell renders only after it is known (US1 AS2)
+- [X] T043 [US1] DESIGN (local machine, Pencil MCP): add to `design.pen` a Language section in personal settings (native names + completeness, current choice), a compact language picker for `/login` and `/share/*` (no internal info), and a mobile variant; export touched nodes to `assets/design-export/json/<id>.json` and `assets/design-export/screenshots/<id>.png` (design-export skill). *Done note: Language card first on `lWvcv` and `T1wkiT` (OD-016), mobile screen `g5e2fM`, compact picker `Jf27F` in the top-right corner of every login and share card (OD-017), menu-open screen `G7OwqK`; details in `assets/design-export/MANIFEST.md`.*
 - [ ] T044 [US1] Implement the personal-settings language section (component `web/src/components/settings/LanguagePicker.tsx`, mounted in `web/src/routes/ThemeSettings.tsx` settings page per the T043 design) calling `Users.setLanguage`, listing only `listed` languages from `languages.json`; tests `LanguagePicker.test.tsx`
 - [ ] T045 [US1] Add the browser-local picker to `web/src/routes/Login.tsx` and `web/src/routes/Share.tsx` (writes `gameplane-language.choice`, reads `Auth.locale` for the default); tests in `Login.test.tsx`, `Share.test.tsx`
-- [ ] T046 [US1] Add the `0%` fixture language behind `VITE_I18N_FIXTURES=1` in the build step of `web/vite.config.ts` (never in release `languages.json`) for SC-008 tests
-- [ ] T047 [US1] Update `web/specs.md` and `api/specs.md` (language resolution, endpoints, boot snippet, problem+json)
+- [X] T046 [US1] Add the `0%` fixture language behind `VITE_I18N_FIXTURES=1` in the build step of `web/vite.config.ts` (never in release `languages.json`) for SC-008 tests
+- [X] T047 [US1] Update `web/specs.md` and `api/specs.md` (language resolution, endpoints, boot snippet, problem+json)
 
 **Checkpoint**: Picker works with English + any listed pack; strings migrate in US4.
 
@@ -116,13 +116,13 @@ description: "Task list for 019 App Localization & Community Language Packs"
 
 ### Tests for User Story 2
 
-- [ ] T048 [P] [US2] CI self-test job step in `.github/workflows/ci.yaml` running `i18n-check` over each `i18n/testdata/defective/*` fixture and asserting a non-zero exit with the expected code (SC-007)
+- [X] T048 [P] [US2] CI self-test job step in `.github/workflows/ci.yaml` running `i18n-check` over each `i18n/testdata/defective/*` fixture and asserting a non-zero exit with the expected code (SC-007)
 
 ### Implementation for User Story 2
 
-- [ ] T049 [US2] Implement `--stamp` and needs-review handling end to end: translations carry `sourceHash`; build drops `invalid` entries so English shows (FR-018); verify the manifest marks a pack under 80% `listed: false` (FR-017)
-- [ ] T050 [US2] Write contributor guide `docs/translating.md` (FR-019): both contribution paths (file PR and Weblate), copying `i18n/locales/en/` to a new tag, writing `meta.json`, ICU plural/select examples, safe tags, running the dev server with a local pack to preview (`make web-dev`), style guide and glossary of fixed/untranslated Gameplane terms (GameServer, module, sentinel, …), what the CI report means; link it from `docs/contributing.md` and `README.md`
-- [ ] T051 [US2] Add a "translation" PR template section or label rule (`type: docs`, `area: shared`) in `.github/` auto-label config so pack PRs are labelled automatically
+- [X] T049 [US2] Implement `--stamp` and needs-review handling end to end: translations carry `sourceHash`; build drops `invalid` entries so English shows (FR-018); verify the manifest marks a pack under 80% `listed: false` (FR-017)
+- [X] T050 [US2] Write contributor guide `docs/translating.md` (FR-019): both contribution paths (file PR and Weblate), copying `i18n/locales/en/` to a new tag, writing `meta.json`, ICU plural/select examples, safe tags, running the dev server with a local pack to preview (`make web-dev`), style guide and glossary of fixed/untranslated Gameplane terms (GameServer, module, sentinel, …), what the CI report means; link it from `docs/contributing.md` and `README.md`
+- [X] T051 [US2] Add a "translation" PR template section or label rule (`type: docs`, `area: shared`) in `.github/` auto-label config so pack PRs are labelled automatically
 
 **Checkpoint**: A partial test pack passes CI and shows in the job summary.
 
@@ -158,23 +158,23 @@ description: "Task list for 019 App Localization & Community Language Packs"
 
 ### Tests for User Story 5
 
-- [ ] T061 [P] [US5] Go API E2E `test/e2e/i18n_problem_json_e2e_test.go`: forbidden-namespace and validation errors return byte-identical text/plain bodies without the Accept header and problem bodies with `detail`, `messageId`, `args` with it; failed login returns only `server.auth.invalid_credentials` for both unknown user and wrong password (FR-030); register in `test/e2e/buckets.sh`
+- [X] T061 [P] [US5] Go API E2E `test/e2e/i18n_problem_json_e2e_test.go`: forbidden-namespace and validation errors return byte-identical text/plain bodies without the Accept header and problem bodies with `detail`, `messageId`, `args` with it; failed login returns only `server.auth.invalid_credentials` for both unknown user and wrong password (FR-030); register in `test/e2e/buckets.sh`
 - [ ] T062 [P] [US5] Go API E2E `test/e2e/i18n_notify_language_e2e_test.go`: webhook sink with `language: "fr"` and one without; test send to both via `POST /api/v1/admin/notifications/sinks/{name}/test`; first payload has `language: "fr"` and French `title`/`text`, second uses instance default; all pre-existing payload fields unchanged; register in `test/e2e/buckets.sh`
-- [ ] T063 [P] [US5] envtest `operator/internal/controller/gameserver_envtest_test.go` additions: `status.conditionArgs` set with the condition and cleared when the reason no longer has args
+- [X] T063 [P] [US5] envtest `operator/internal/controller/gameserver_envtest_test.go` additions: `status.conditionArgs` set with the condition and cleared when the reason no longer has args (done in the new file `gameserver_condition_args_envtest_test.go`, next to the condition-args code)
 
 ### Implementation for User Story 5
 
-- [ ] T064 [US5] Migrate the 193 direct `http.Error` calls in `api/internal/handlers/*.go`, `api/internal/auth/*.go` and `api/internal/ws/*.go` to `httperr.WriteMessage` with registry ids (English text unchanged), batched per file by a scripted transform; add each id to `api/internal/messages/messages.go`; run `make i18n-sync`
-- [ ] T065 [US5] Ensure unauthenticated paths (`api/internal/auth/local.go`, OIDC handlers, `MountPublicShares`) only emit `server.auth.invalid_credentials` / `server.generic.*` ids (FR-030, rule 3); tests in `api/internal/auth/local_test.go`
-- [ ] T066 [US5] Add `ConditionArgs map[string]map[string]string` (`json:"conditionArgs,omitempty"`) to `GameServerStatus` in `operator/api/v1alpha1/gameserver_types.go`; run `make generate && make manifests`; commit deepcopy, `operator/config/crd/*.yaml`, `charts/gameplane/crds/*.yaml` / `crd-manifests/` in the same commit (rule 7)
-- [ ] T067 [US5] Set `status.conditionArgs` alongside every operator-authored condition that interpolates values into its message in `operator/internal/controller/gameserver_controller.go` (and helpers), keeping the English `message` unchanged; update `operator/specs.md`
-- [ ] T068 [US5] Add `condition.<type>.<reason>` English entries for all operator reasons (66 literals in `operator/internal/controller/`) to `i18n/locales/en/app.json` via a generator `operator/hack/condition-ids.go` invoked by `make i18n-sync`, with descriptions
-- [ ] T069 [US5] Add mirrored `conditionArgs` to the GameServer type in `web/src/types.ts`
-- [ ] T070 [US5] Add a `Language` field (JSON `language,omitempty`) to `Sink` in `api/internal/notify/sinks.go`; accept and validate it in `validateNotifications` (`api/internal/handlers/config.go`, unknown tag → `server.i18n.unknown_language`)
-- [ ] T071 [US5] Localize `api/internal/notify/format.go`: `title`/`detail`/test copy rendered from `notify.*` entries via `i18n/catalog.Lookup` in sink language → instance default (config `i18n`) → `en`; webhook payload adds `language`, `title`, `text` and keeps existing fields; Kubernetes `Reason`/`Message` verbatim (FR-011); add the `notify.*` English entries with descriptions to `i18n/locales/en/app.json`; tests in `api/internal/notify/format_test.go`, `sinks_test.go`
-- [ ] T072 [US5] DESIGN (local machine, Pencil MCP): add a Language field to the notification destination form in `design.pen`; export touched nodes to `assets/design-export/`
+- [X] T064 [US5] Migrate the 193 direct `http.Error` calls in `api/internal/handlers/*.go`, `api/internal/auth/*.go` and `api/internal/ws/*.go` to `httperr.WriteMessage` with registry ids (English text unchanged), batched per file by a scripted transform; add each id to `api/internal/messages/messages.go`; run `make i18n-sync`
+- [X] T065 [US5] Ensure unauthenticated paths (`api/internal/auth/local.go`, OIDC handlers, `MountPublicShares`) only emit `server.auth.invalid_credentials` / `server.generic.*` ids (FR-030, rule 3); tests in `api/internal/auth/local_test.go`
+- [X] T066 [US5] Add `ConditionArgs map[string]map[string]string` (`json:"conditionArgs,omitempty"`) to `GameServerStatus` in `operator/api/v1alpha1/gameserver_types.go`; run `make generate && make manifests`; commit deepcopy, `operator/config/crd/*.yaml`, `charts/gameplane/crds/*.yaml` / `crd-manifests/` in the same commit (rule 7)
+- [X] T067 [US5] Set `status.conditionArgs` alongside every operator-authored condition that interpolates values into its message in `operator/internal/controller/gameserver_controller.go` (and helpers), keeping the English `message` unchanged; update `operator/specs.md`
+- [X] T068 [US5] Add `condition.<type>.<reason>` English entries for all operator reasons (66 literals in `operator/internal/controller/`) to `i18n/locales/en/app.json` via a generator `operator/hack/condition-ids.go` invoked by `make i18n-sync`, with descriptions
+- [X] T069 [US5] Add mirrored `conditionArgs` to the GameServer type in `web/src/types.ts`
+- [X] T070 [US5] Add a `Language` field (JSON `language,omitempty`) to `Sink` in `api/internal/notify/sinks.go`; accept and validate it in `validateNotifications` (`api/internal/handlers/config.go`, unknown tag → `server.i18n.unknown_language`)
+- [X] T071 [US5] Localize `api/internal/notify/format.go`: `title`/`detail`/test copy rendered from `notify.*` entries via `i18n/catalog.Lookup` in sink language → instance default (config `i18n`) → `en`; webhook payload adds `language`, `title`, `text` and keeps existing fields; Kubernetes `Reason`/`Message` verbatim (FR-011); add the `notify.*` English entries with descriptions to `i18n/locales/en/app.json`; tests in `api/internal/notify/format_test.go`, `sinks_test.go`
+- [X] T072 [US5] DESIGN (local machine, Pencil MCP): add a Language field to the notification destination form in `design.pen`; export touched nodes to `assets/design-export/`. *Done note: the design had no destination form, so the Add sink form is a new screen `eaNkj` with the Language select, and each sink row on `n6Xlo` has its own Language select (OD-015).*
 - [ ] T073 [US5] Implement the sink language field in the notifications section of `web/src/routes/AdminSettings.tsx` per T072 design (default "Instance default"); tests `AdminSettings_notifications.test.tsx`
-- [ ] T074 [US5] Update `api/specs.md` and `docs/notifications.md` (per-destination language, webhook fields)
+- [X] T074 [US5] Update `api/specs.md` and `docs/notifications.md` (per-destination language, webhook fields)
 
 **Checkpoint**: French dashboard shows French server errors; French sink receives French notifications.
 
@@ -204,16 +204,16 @@ description: "Task list for 019 App Localization & Community Language Packs"
 
 ### Tests for User Story 6
 
-- [ ] T082 [P] [US6] Go API E2E `test/e2e/i18n_module_locales_e2e_test.go`: push a test module with `locales/fr.json` (hold `ociPushMu`), install, `GET /api/v1/modules/{name}/locales/fr` returns entries; a second module with a bad placeholder installs, reports `LocalesValid=False` and a Warning event, and serves only valid entries; register in `test/e2e/buckets.sh`
-- [ ] T083 [P] [US6] envtest `operator/internal/controller/gametemplate_envtest_test.go` additions: ConfigMap `<template>-locales` owned by the GameTemplate, invalid entries dropped, condition and event set
+- [X] T082 [P] [US6] Go API E2E `test/e2e/i18n_module_locales_e2e_test.go`: push a test module with `locales/fr.json` (hold `ociPushMu`), install, `GET /api/v1/modules/{name}/locales/fr` returns entries; a second module with a bad placeholder installs, reports `LocalesValid=False` and a Warning event, and serves only valid entries; register in `test/e2e/buckets.sh`
+- [X] T083 [P] [US6] envtest `operator/internal/controller/gametemplate_envtest_test.go` additions: ConfigMap `<template>-locales` owned by the GameTemplate, invalid entries dropped, condition and event set
 
 ### Implementation for User Story 6
 
-- [ ] T084 [US6] Implement module id derivation `gp-module/internal/i18n/ids.go` per contracts/module-locales.md §1 (reversible `~0`/`~1` escaping) (shared with the operator through `i18n/pack` helpers if needed) and command `gp-module i18n extract` writing `locales/en.json` with descriptions; tests
-- [ ] T085 [US6] Extend `gp-module validate` to run `i18n/pack` validation in module mode and `gp-module package` to add one layer per `locales/<tag>.json` (media type `application/vnd.gameplane.module.locale.v1+json`, title annotation `locales/<tag>.json`, `en.json` excluded) in `gp-module/internal/packager/packager.go`; update `gp-module/specs.md`; tests
-- [ ] T086 [US6] Add `MediaTypeLocale` and locale-layer extraction to `operator/internal/oci/bundle.go`; tests
-- [ ] T087 [US6] In the GameTemplate reconciler (`operator/internal/controller/`), validate locale layers against ids from the bundled template, write valid entries to ConfigMap `<template>-locales` (owner ref), set `LocalesValid` condition and emit a Warning event listing up to 20 problems; enforce the 900 KiB aggregate bound with reason `LocalesTooLarge` (contracts/module-locales.md §3); module install never fails on locales (FR-034); RBAC markers for ConfigMaps if missing, then `make manifests`; update `operator/specs.md`
-- [ ] T088 [US6] Add `GET /modules/{name}/locales/{tag}` in `api/internal/handlers/modules.go` (same RBAC as `GET /modules/{name}`, regional → base → `{}` resolution); client method in `web/src/lib/endpoints.ts`; handler tests
+- [X] T084 [US6] Implement module id derivation `gp-module/internal/i18n/ids.go` per contracts/module-locales.md §1 (reversible `~0`/`~1` escaping) (shared with the operator through `i18n/pack` helpers if needed) and command `gp-module i18n extract` writing `locales/en.json` with descriptions; tests
+- [X] T085 [US6] Extend `gp-module validate` to run `i18n/pack` validation in module mode and `gp-module package` to add one layer per `locales/<tag>.json` (media type `application/vnd.gameplane.module.locale.v1+json`, title annotation `locales/<tag>.json`, `en.json` excluded) in `gp-module/internal/packager/packager.go`; update `gp-module/specs.md`; tests
+- [X] T086 [US6] Add `MediaTypeLocale` and locale-layer extraction to `operator/internal/oci/bundle.go`; tests
+- [X] T087 [US6] In the GameTemplate reconciler (`operator/internal/controller/`), validate locale layers against ids from the bundled template, write valid entries to ConfigMap `<template>-locales` (owner ref), set `LocalesValid` condition and emit a Warning event listing up to 20 problems; enforce the 900 KiB aggregate bound with reason `LocalesTooLarge` (contracts/module-locales.md §3); module install never fails on locales (FR-034); RBAC markers for ConfigMaps if missing, then `make manifests`; update `operator/specs.md`
+- [X] T088 [US6] Add `GET /modules/{name}/locales/{tag}` in `api/internal/handlers/modules.go` (same RBAC as `GET /modules/{name}`, regional → base → `{}` resolution); client method in `web/src/lib/endpoints.ts`; handler tests
 - [ ] T089 [US6] Use module locale maps in `web/src/routes/CreateServer.tsx` and the server-settings tab (`web/src/routes/tabs/settings/**`) with fallback to template text (FR-032); tests
 - [ ] T090 [US6] [module repo] Push locale layers in `modules/build.sh` (`locales/*.json` except `en.json`) and run `i18n-check --module` in the module repo CI; update `modules/README.md`
 - [ ] T091 [US6] [module repo] Generate `locales/en.json` for `modules/minecraft-java/`, `modules/terraria/`, `modules/valheim/` with `gp-module i18n extract`; update each module's `specs.md`; open the module-repo PR; bump the root `modules` pointer only after it merges
@@ -227,8 +227,8 @@ description: "Task list for 019 App Localization & Community Language Packs"
 **Independent Test**: quickstart.md scenario 4.
 
 - [ ] T092 [P] [US7] Go API E2E `test/e2e/i18n_instance_default_e2e_test.go`: `PUT /api/v1/admin/config/i18n` `{defaultLanguage:"fr"}` → `GET /auth/locale` returns `fr`; unlisted tag → 400 `server.i18n.unlisted_language`; non-admin → 403; register in `test/e2e/buckets.sh`
-- [ ] T093 [US7] Add config section `i18n` with `validateI18n` (listed languages only) to the validators map in `api/internal/handlers/config.go`; register `server.i18n.unlisted_language`; tests `config_validators_test.go`
-- [ ] T094 [US7] DESIGN (local machine, Pencil MCP): add a Default language field to admin settings in `design.pen`; export touched nodes to `assets/design-export/`
+- [X] T093 [US7] Add config section `i18n` with `validateI18n` (listed languages only) to the validators map in `api/internal/handlers/config.go`; register `server.i18n.unlisted_language`; tests `config_validators_test.go`
+- [X] T094 [US7] DESIGN (local machine, Pencil MCP): add a Default language field to admin settings in `design.pen`; export touched nodes to `assets/design-export/`. *Done note: on `WZdnw` the field is in its own Language card with its own Save changes button, below the General card, because it is saved to the separate config section `i18n`.*
 - [ ] T095 [US7] Implement the Default language field in `web/src/routes/AdminSettings.tsx` per T094; tests `AdminSettings_sections.test.tsx`
 
 ---
@@ -240,15 +240,15 @@ description: "Task list for 019 App Localization & Community Language Packs"
 - [ ] T096 Create `i18n/locales/fr/meta.json` (`fr`, `Français`, `French`, `ltr`, credits)
 - [ ] T097 Translate `i18n/locales/fr/app.json` to 100% (web, server, condition, notify, audit); drafts may be machine-assisted but every entry is approved by a native French reviewer on Weblate or in PR review; `i18n-check` shows fr 100% and listed
 - [ ] T098 [module repo] Translate `modules/minecraft-java/locales/fr.json`, `modules/terraria/locales/fr.json`, `modules/valheim/locales/fr.json` to 100%; module-repo PR; root pointer bump after merge
-- [ ] T099 Implement pseudo-language `en-XA` generation (accented, ~40% longer, bracketed) behind `VITE_I18N_PSEUDO=1` in the `web/vite.config.ts` build step; never present in release `languages.json` (FR-038)
+- [X] T099 Implement pseudo-language `en-XA` generation (accented, ~40% longer, bracketed) behind `VITE_I18N_PSEUDO=1` in the `web/vite.config.ts` build step; never present in release `languages.json` (FR-038)
 - [ ] T100 Add an `en-XA` project to `web/playwright.config.ts` running the screenshot suite (`web/e2e/screenshots/`), and fix clipping/overlap found (truncation must reveal full text on hover/focus, FR-010); any visual change goes through `design.pen` first (local machine)
 
 ---
 
 ## Phase 11: Polish & Cross-Cutting Concerns
 
-- [ ] T101 [P] Update `docs/architecture.md`, `docs/agent-architecture.md` (task → doc map entry for i18n) and `docs/module-authoring.md` (module translations section)
-- [ ] T102 [P] Add a CHANGELOG / release-notes entry describing language selection, French, problem+json negotiation (opt-in) and module translations
+- [X] T101 [P] Update `docs/architecture.md`, `docs/agent-architecture.md` (task → doc map entry for i18n) and `docs/module-authoring.md` (module translations section)
+- [X] T102 [P] Add a CHANGELOG / release-notes entry describing language selection, French, problem+json negotiation (opt-in) and module translations
 - [ ] T103 Run quickstart.md scenarios 1–13 against a `make dev-up` cluster and record results in the PR description
 - [ ] T104 Confirm the coverage gates (`i18n` 90, api 80, operator 72, gp-module 80, web thresholds) pass on CI; add tests where they do not (never lower thresholds)
 - [ ] T105 After merge and with every task complete or withdrawn: `git mv specs/019-localization-language-packs specs/done_019-localization-language-packs` and update in-repo references (Constitution IV, rule 16)
diff --git a/specs/done_010-easy-module-building/contracts/diagnostics-contract.md b/specs/done_010-easy-module-building/contracts/diagnostics-contract.md
index 05148db84..4e0fb58c6 100644
--- a/specs/done_010-easy-module-building/contracts/diagnostics-contract.md
+++ b/specs/done_010-easy-module-building/contracts/diagnostics-contract.md
@@ -24,6 +24,7 @@ This contract defines the rule catalog, severity levels, diagnostic message form
 | `credential-field-not-password` | **ERROR** | `template.yaml` | Field name contains credential substrings (`PASSWORD`, `TOKEN`, `SECRET`, `KEY`, `AUTH`) but `type` is not `password`. | Set `type: password` so the operator stores value securely in a Secret instead of plaintext CR. |
 | `excessive-asset-size` | **WARN** | Assets | Asset `icon.png` exceeds 512 KiB or total directory size exceeds 1 MiB. | Compress asset or reduce resolution to optimize OCI bundle transfer. |
 | `gameplane-min-version-exceeds-tool` | **WARN** | `module.yaml` | `gameplaneMinVersion` is a valid semver higher than this `gp-module`'s own version. | Lower `gameplaneMinVersion` to match a released Gameplane version, or upgrade `gp-module`/the operator before publishing. |
+| `locale-id-invalid` | **ERROR** | `template.yaml` (`module.yaml` for `module.*` ids) | A translation id derived from `module.yaml` or `template.yaml` (for example a config key or option value) fails the module id rule `modlocale.ValidID`, because it contains a space, `/`, `:` or another symbol outside `[A-Za-z0-9_~-.]`. | Rename the key or option value so it contains no spaces, `/`, `:` or other symbols; translators cannot target it otherwise. |
 
 ---
 
diff --git a/test/e2e/buckets.sh b/test/e2e/buckets.sh
index 28fcd35a2..c75e02f72 100755
--- a/test/e2e/buckets.sh
+++ b/test/e2e/buckets.sh
@@ -123,9 +123,13 @@ TestAPI_PasswordResetInvalidatesSession
 TestAPI_OIDCHelmSeeded_AdminOnFirstLogin
 TestAPI_OIDCHelmSeeded_DefaultRoleOnNoMapping
 TestAPI_OIDCHelmSeeded_RoleReevaluatedOnGroupChange
+TestAPI_I18n_AuthLocale
 EOF
 }
 
+# TestAPI_I18n_AuthLocale (spec 019, T036) reads the pre-auth GET /auth/locale
+# on a fresh install. It never logs in, so it spends no admin-login budget.
+
 # The three TestAPI_OIDCHelmSeeded_* tests above spend 0 of this bucket's
 # admin-login budget: they authenticate entirely as OIDC users against a
 # fake in-cluster IdP (test/e2e/internal/fakeoidc), never as e2e-admin,
@@ -326,15 +330,21 @@ EOF
 # multicluster_e2e_test.go's package doc. Its own dedicated CI job
 # (e2e-multicluster) brings up both clusters before running it.
 #
-# TestAPI_AccountRemoval_RevokesSharesAndAllowsSSOReprovision and
-# TestAPI_ModuleUpload_ExtractionStaysWithinBudget live here for the login
-# budget, not by subject: api-mods is at its ~7 e2e-admin-login ceiling. Each
-# costs +1 e2e-admin login (account removal also uses fake-OIDC sign-ins,
-# which every e2e.sh cluster deploys), bringing this job to 3; both run
-# against the primary cluster.
+# TestAPI_AccountRemoval_RevokesSharesAndAllowsSSOReprovision,
+# TestAPI_ModuleUpload_ExtractionStaysWithinBudget, TestAPI_I18n_ProblemJSON
+# and TestAPI_I18n_ModuleLocales live here for the login budget, not by
+# subject: api-mods is at its ~7 e2e-admin-login ceiling. Each costs +1
+# e2e-admin login (account removal also uses fake-OIDC sign-ins, which every
+# e2e.sh cluster deploys), and TestAPI_I18n_ProblemJSON costs one admin login,
+# one viewer login and one failed-login pair, bringing this job to 5 admin
+# logins (ceiling ~7). All run against the primary cluster. api-auth,
+# api-roles, api-mods, api-rbac and api-agent are at their ceilings (see their
+# comments); do not add to them.
 bucket_multicluster() { cat <<'EOF'
 TestAPI_AccountRemoval_RevokesSharesAndAllowsSSOReprovision
 TestAPI_ModuleUpload_ExtractionStaysWithinBudget
+TestAPI_I18n_ProblemJSON
+TestAPI_I18n_ModuleLocales
 TestMultiCluster_ClusterDispatchAndScopedRBAC
 TestMultiCluster_GatewayParity
 EOF
diff --git a/test/e2e/fixtures/oras-push-i18n-bad.yaml b/test/e2e/fixtures/oras-push-i18n-bad.yaml
new file mode 100644
index 000000000..fa1607cd0
--- /dev/null
+++ b/test/e2e/fixtures/oras-push-i18n-bad.yaml
@@ -0,0 +1,86 @@
+# Module bundle with a French translation layer, pushed to the in-cluster
+# registry by TestAPI_I18n_ModuleLocales. ConfigMap keys cannot contain "/", so
+# the locale file is stored as locales-fr.json and mounted at locales/fr.json:
+# oras then records the layer title "locales/fr.json".
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: gameplane-test-module-bundle-i18n-bad
+  namespace: gameplane-system
+  labels:
+    app.kubernetes.io/component: e2e-fixture
+data:
+  module.yaml: |
+    apiVersion: gameplane.local/module/v1
+    name: e2e-i18n-bad
+    displayName: E2E I18n Bad
+    version: 0.1.0
+    game: e2e-i18n-bad
+    summary: Module with an invalid French entry
+    license: MIT
+    gameplaneMinVersion: 0.1.0
+  template.yaml: |
+    apiVersion: gameplane.local/v1alpha1
+    kind: GameTemplate
+    metadata:
+      name: e2e-i18n-bad
+      labels:
+        gameplane.local/module: e2e-i18n-bad
+    spec:
+      displayName: E2E I18n Bad
+      game: e2e-i18n-bad
+      version: "0.1.0"
+      image: busybox:1.36
+      command: ["sh", "-c", "sleep 100000"]
+      ports:
+        - name: noop
+          containerPort: 12345
+          advertise: true
+          protocol: TCP
+  locales-fr.json: |
+    {
+      "template.displayName": {"defaultMessage": "Jeu de test"},
+      "module.summary": {"defaultMessage": "Module {extra}"}
+    }
+---
+apiVersion: batch/v1
+kind: Job
+metadata:
+  name: oras-push-i18n-bad
+  namespace: gameplane-system
+  labels:
+    app.kubernetes.io/component: e2e-fixture
+spec:
+  backoffLimit: 4
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/component: e2e-fixture
+    spec:
+      restartPolicy: OnFailure
+      containers:
+        - name: push
+          image: ghcr.io/oras-project/oras:v1.3.3
+          command: ["oras"]
+          args:
+            - push
+            - --plain-http
+            - --artifact-type=application/vnd.gameplane.module.v1+json
+            - gameplane-test-registry.gameplane-system.svc:5000/e2e-i18n-bad:0.1.0
+            - module.yaml:application/vnd.gameplane.module.metadata.v1+yaml
+            - template.yaml:application/vnd.gameplane.module.template.v1+yaml
+            - locales/fr.json:application/vnd.gameplane.module.locale.v1+json
+          workingDir: /workspace
+          volumeMounts:
+            - { name: bundle, mountPath: /workspace }
+            - { name: tmp,    mountPath: /tmp }
+      volumes:
+        - name: bundle
+          configMap:
+            name: gameplane-test-module-bundle-i18n-bad
+            items:
+              - { key: module.yaml, path: module.yaml }
+              - { key: template.yaml, path: template.yaml }
+              - { key: locales-fr.json, path: locales/fr.json }
+        - name: tmp
+          emptyDir: {}
diff --git a/test/e2e/fixtures/oras-push-i18n-fr.yaml b/test/e2e/fixtures/oras-push-i18n-fr.yaml
new file mode 100644
index 000000000..a7e1b8776
--- /dev/null
+++ b/test/e2e/fixtures/oras-push-i18n-fr.yaml
@@ -0,0 +1,86 @@
+# Module bundle with a French translation layer, pushed to the in-cluster
+# registry by TestAPI_I18n_ModuleLocales. ConfigMap keys cannot contain "/", so
+# the locale file is stored as locales-fr.json and mounted at locales/fr.json:
+# oras then records the layer title "locales/fr.json".
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: gameplane-test-module-bundle-i18n-fr
+  namespace: gameplane-system
+  labels:
+    app.kubernetes.io/component: e2e-fixture
+data:
+  module.yaml: |
+    apiVersion: gameplane.local/module/v1
+    name: e2e-i18n-fr
+    displayName: E2E I18n Fr
+    version: 0.1.0
+    game: e2e-i18n-fr
+    summary: Module with a valid French translation
+    license: MIT
+    gameplaneMinVersion: 0.1.0
+  template.yaml: |
+    apiVersion: gameplane.local/v1alpha1
+    kind: GameTemplate
+    metadata:
+      name: e2e-i18n-fr
+      labels:
+        gameplane.local/module: e2e-i18n-fr
+    spec:
+      displayName: E2E I18n Fr
+      game: e2e-i18n-fr
+      version: "0.1.0"
+      image: busybox:1.36
+      command: ["sh", "-c", "sleep 100000"]
+      ports:
+        - name: noop
+          containerPort: 12345
+          advertise: true
+          protocol: TCP
+  locales-fr.json: |
+    {
+      "template.displayName": {"defaultMessage": "Jeu de test"},
+      "module.summary": {"defaultMessage": "Module de test"}
+    }
+---
+apiVersion: batch/v1
+kind: Job
+metadata:
+  name: oras-push-i18n-fr
+  namespace: gameplane-system
+  labels:
+    app.kubernetes.io/component: e2e-fixture
+spec:
+  backoffLimit: 4
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/component: e2e-fixture
+    spec:
+      restartPolicy: OnFailure
+      containers:
+        - name: push
+          image: ghcr.io/oras-project/oras:v1.3.3
+          command: ["oras"]
+          args:
+            - push
+            - --plain-http
+            - --artifact-type=application/vnd.gameplane.module.v1+json
+            - gameplane-test-registry.gameplane-system.svc:5000/e2e-i18n-fr:0.1.0
+            - module.yaml:application/vnd.gameplane.module.metadata.v1+yaml
+            - template.yaml:application/vnd.gameplane.module.template.v1+yaml
+            - locales/fr.json:application/vnd.gameplane.module.locale.v1+json
+          workingDir: /workspace
+          volumeMounts:
+            - { name: bundle, mountPath: /workspace }
+            - { name: tmp,    mountPath: /tmp }
+      volumes:
+        - name: bundle
+          configMap:
+            name: gameplane-test-module-bundle-i18n-fr
+            items:
+              - { key: module.yaml, path: module.yaml }
+              - { key: template.yaml, path: template.yaml }
+              - { key: locales-fr.json, path: locales/fr.json }
+        - name: tmp
+          emptyDir: {}
diff --git a/test/e2e/go.mod b/test/e2e/go.mod
index 490c379d0..53cbf4fba 100644
--- a/test/e2e/go.mod
+++ b/test/e2e/go.mod
@@ -6,6 +6,10 @@ require github.com/GameplanePanel/gameplane/gp-module v0.0.0
 
 replace github.com/GameplanePanel/gameplane/gp-module => ../../gp-module
 
+require github.com/GameplanePanel/gameplane/i18n v0.0.0
+
+replace github.com/GameplanePanel/gameplane/i18n => ../../i18n
+
 require github.com/GameplanePanel/gameplane/telemetryschema v0.0.0
 
 replace github.com/GameplanePanel/gameplane/telemetryschema => ../../telemetryschema
@@ -56,7 +60,7 @@ require (
 	golang.org/x/oauth2 v0.36.0 // indirect
 	golang.org/x/sys v0.47.0 // indirect
 	golang.org/x/term v0.45.0 // indirect
-	golang.org/x/text v0.41.0 // indirect
+	golang.org/x/text v0.42.0 // indirect
 	golang.org/x/time v0.15.0 // indirect
 	google.golang.org/protobuf v1.36.12 // indirect
 	gopkg.in/evanphx/json-patch.v4 v4.13.0 // indirect
diff --git a/test/e2e/go.sum b/test/e2e/go.sum
index 6880fa1d8..0462a4ba5 100644
--- a/test/e2e/go.sum
+++ b/test/e2e/go.sum
@@ -77,9 +77,9 @@ github.com/spf13/pflag v1.0.10/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3A
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.5.3 h1:jmXUvGomnU1o3W/V5h2VEradbpJDwGrzugQQvL0POH4=
 github.com/stretchr/objx v0.5.3/go.mod h1:rDQraq+vQZU7Fde9LOZLr8Tax6zZvy4kuNKF+QYS+U0=
-github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/vishvananda/netlink v1.1.0 h1:1iyaYNBLmP6L0220aDnYQpo1QEV4t4hJ+xEEhhJH8j0=
 github.com/vishvananda/netlink v1.1.0/go.mod h1:cTgwzPIzzgDAYoQrMm0EdrjRUBkTqKYppBueQtXaqoE=
 github.com/vishvananda/netns v0.0.0-20211101163701-50045581ed74 h1:gga7acRE695APm9hlsSMoOoE65U4/TcqNj90mc69Rlg=
@@ -100,6 +100,8 @@ golang.org/x/term v0.45.0 h1:NwWyBmoJCbfTHpxrWoZ9C6/VxOf7ic219I8xZZFdrf0=
 golang.org/x/term v0.45.0/go.mod h1:9aqxs0blBcrm/n0L9QW0aRVD+ktan8ssZromtqJC43w=
 golang.org/x/text v0.41.0 h1:vz/seA0lnX87Othu2f/0L24RcgrXD9/YFTSuGjj3rH8=
 golang.org/x/text v0.41.0/go.mod h1:jvf1O8ajNzZqhSrQBPbutR/EB83Cc0CFrezNQIwbb5M=
+golang.org/x/text v0.42.0 h1:JbOZXgfeCPU9gacVtYliJqOhD+zhrEqK4LfdpmlUZqI=
+golang.org/x/text v0.42.0/go.mod h1:ojzP1Z+2QtioaF8DTtO8K5q7JWVVYwZKenzujK0Zd0E=
 golang.org/x/time v0.15.0 h1:bbrp8t3bGUeFOx08pvsMYRTCVSMk89u4tKbNOZbp88U=
 golang.org/x/time v0.15.0/go.mod h1:Y4YMaQmXwGQZoFaVFk4YpCt4FLQMYKZe9oeV/f4MSno=
 google.golang.org/protobuf v1.36.12 h1:pJOKDDOyeXErUroCihFAd5LQuwXBSpVnKGrj5o/fwxc=
diff --git a/test/e2e/i18n_auth_locale_e2e_test.go b/test/e2e/i18n_auth_locale_e2e_test.go
new file mode 100644
index 000000000..77f5ee9ac
--- /dev/null
+++ b/test/e2e/i18n_auth_locale_e2e_test.go
@@ -0,0 +1,55 @@
+//go:build e2e
+
+package e2e
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"testing"
+)
+
+// TestAPI_I18n_AuthLocale proves the pre-auth GET /auth/locale endpoint on a
+// fresh install: it answers without a session and returns exactly one key,
+// defaultLanguage, set to "en". It never logs in, so it spends no login
+// budget, and it can run in parallel with its bucket neighbours.
+func TestAPI_I18n_AuthLocale(t *testing.T) {
+	t.Parallel()
+
+	port, stop := envInstance.PortForward(t, "gameplane-system", "svc/gameplane-api", 80)
+	defer stop()
+
+	req, err := http.NewRequestWithContext(t.Context(), http.MethodGet,
+		fmt.Sprintf("http://127.0.0.1:%d/auth/locale", port), nil)
+	if err != nil {
+		t.Fatalf("build request: %v", err)
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatalf("do: %v", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatalf("read body: %v", err)
+	}
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("GET /auth/locale: status %d, body=%s", resp.StatusCode, body)
+	}
+
+	var got map[string]any
+	if err := json.Unmarshal(body, &got); err != nil {
+		t.Fatalf("decode: %v; body=%s", err, body)
+	}
+	if len(got) != 1 {
+		t.Fatalf("want exactly one key, got %d; body=%s", len(got), body)
+	}
+	lang, ok := got["defaultLanguage"].(string)
+	if !ok {
+		t.Fatalf("defaultLanguage missing or not a string; body=%s", body)
+	}
+	if lang != "en" {
+		t.Fatalf("defaultLanguage = %q, want en on a fresh install", lang)
+	}
+}
diff --git a/test/e2e/i18n_module_locales_e2e_test.go b/test/e2e/i18n_module_locales_e2e_test.go
new file mode 100644
index 000000000..4cdf66efa
--- /dev/null
+++ b/test/e2e/i18n_module_locales_e2e_test.go
@@ -0,0 +1,226 @@
+//go:build e2e
+
+package e2e
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"strings"
+	"testing"
+	"time"
+
+	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+)
+
+// TestAPI_I18n_ModuleLocales covers module translations end to end: a bundle
+// whose "locales/fr.json" layer is valid is served by GET
+// /modules/{name}/locales/{tag}; a bundle whose French layer holds one valid
+// and one invalid entry installs anyway, serves only the valid entry, and
+// reports the problem as a LocalesValid=False condition and a Warning event
+// on the GameTemplate.
+//
+// Budget: one e2e-admin login. It runs on the primary cluster.
+func TestAPI_I18n_ModuleLocales(t *testing.T) {
+	t.Parallel()
+	// Shares the fixed-name registry and the oras push Jobs with the other
+	// module tests.
+	ociPushMu.Lock()
+	defer ociPushMu.Unlock()
+
+	ctx := context.Background()
+
+	envInstance.ApplyYAML(t, "oci-registry.yaml")
+	envInstance.Eventually(t, 90*time.Second, func() (bool, string) {
+		dep, err := envInstance.K8s.AppsV1().Deployments("gameplane-system").
+			Get(ctx, "gameplane-test-registry", metav1.GetOptions{})
+		if err != nil {
+			return false, "get registry deploy: " + err.Error()
+		}
+		if dep.Status.ReadyReplicas >= 1 {
+			return true, ""
+		}
+		return false, "registry not ready yet"
+	})
+
+	envInstance.OCIPushFromFixture(t, "gameplane-system", "oras-push-i18n-fr", "oras-push-i18n-fr.yaml")
+	envInstance.OCIPushFromFixture(t, "gameplane-system", "oras-push-i18n-bad", "oras-push-i18n-bad.yaml")
+
+	const (
+		sourceName = "e2e-i18n-source"
+		goodModule = "e2e-i18n-fr"
+		badModule  = "e2e-i18n-bad"
+	)
+
+	src := &unstructured.Unstructured{Object: map[string]any{
+		"apiVersion": "gameplane.local/v1alpha1",
+		"kind":       "ModuleSource",
+		"metadata":   map[string]any{"name": sourceName},
+		"spec": map[string]any{
+			"type": "oci",
+			"oci": map[string]any{
+				"url":      "gameplane-test-registry.gameplane-system.svc:5000",
+				"insecure": true,
+				"modules": []any{
+					map[string]any{"name": goodModule},
+					map[string]any{"name": badModule},
+				},
+			},
+			"refreshInterval": "10m",
+		},
+	}}
+	if _, err := envInstance.Dyn.Resource(moduleSourceGVR).
+		Create(ctx, src, metav1.CreateOptions{}); err != nil && !apierrors.IsAlreadyExists(err) {
+		t.Fatalf("create modulesource: %v", err)
+	}
+	t.Cleanup(func() {
+		_ = envInstance.Dyn.Resource(moduleSourceGVR).
+			Delete(context.Background(), sourceName, metav1.DeleteOptions{})
+	})
+	envInstance.Eventually(t, 90*time.Second, func() (bool, string) {
+		got, err := envInstance.Dyn.Resource(moduleSourceGVR).Get(ctx, sourceName, metav1.GetOptions{})
+		if err != nil {
+			return false, "get modulesource: " + err.Error()
+		}
+		modules, _, _ := unstructured.NestedSlice(got.Object, "status", "modules")
+		if len(modules) < 2 {
+			return false, "status.modules has fewer than two entries"
+		}
+		return true, ""
+	})
+
+	for _, name := range []string{goodModule, badModule} {
+		mod := &unstructured.Unstructured{Object: map[string]any{
+			"apiVersion": "gameplane.local/v1alpha1",
+			"kind":       "Module",
+			"metadata":   map[string]any{"name": name},
+			"spec": map[string]any{
+				"source":  map[string]any{"name": sourceName},
+				"name":    name,
+				"version": "0.1.0",
+			},
+		}}
+		if _, err := envInstance.Dyn.Resource(moduleGVR).
+			Create(ctx, mod, metav1.CreateOptions{}); err != nil && !apierrors.IsAlreadyExists(err) {
+			t.Fatalf("create module %s: %v", name, err)
+		}
+		modName := name
+		t.Cleanup(func() {
+			_ = envInstance.Dyn.Resource(moduleGVR).
+				Delete(context.Background(), modName, metav1.DeleteOptions{})
+		})
+	}
+	for _, name := range []string{goodModule, badModule} {
+		modName := name
+		envInstance.Eventually(t, 2*time.Minute, func() (bool, string) {
+			got, err := envInstance.Dyn.Resource(moduleGVR).Get(ctx, modName, metav1.GetOptions{})
+			if err != nil {
+				return false, "get module: " + err.Error()
+			}
+			phase, _, _ := unstructured.NestedString(got.Object, "status", "phase")
+			if phase != "Ready" {
+				lastErr, _, _ := unstructured.NestedString(got.Object, "status", "lastError")
+				return false, modName + " phase=" + phase + " lastError=" + lastErr
+			}
+			return true, ""
+		})
+	}
+
+	envInstance.BootstrapAdmin(t, adminUsername, adminPassword)
+	admin := envInstance.APIClient(t, adminUsername, adminPassword)
+	defer admin.Close()
+
+	getLocales := func(module, tag string) (int, map[string]string) {
+		t.Helper()
+		resp, body, err := admin.Get("/modules/" + module + "/locales/" + tag)
+		if err != nil {
+			t.Fatalf("GET locales %s/%s: %v", module, tag, err)
+		}
+		defer func() { _ = resp.Body.Close() }()
+		if resp.StatusCode != http.StatusOK {
+			return resp.StatusCode, nil
+		}
+		var out map[string]string
+		if err := json.Unmarshal(body, &out); err != nil {
+			t.Fatalf("decode %s/%s: %v (%s)", module, tag, err, body)
+		}
+		return resp.StatusCode, out
+	}
+
+	t.Run("ValidTranslationIsServed", func(t *testing.T) {
+		code, got := getLocales(goodModule, "fr")
+		if code != http.StatusOK {
+			t.Fatalf("status = %d", code)
+		}
+		if got["template.displayName"] != "Jeu de test" || got["module.summary"] != "Module de test" {
+			t.Errorf("fr = %v", got)
+		}
+	})
+
+	t.Run("RegionalTagFallsBackToBaseLanguage", func(t *testing.T) {
+		_, got := getLocales(goodModule, "fr-CA")
+		if got["template.displayName"] != "Jeu de test" {
+			t.Errorf("fr-CA = %v", got)
+		}
+	})
+
+	t.Run("UnknownLanguageIsEmpty", func(t *testing.T) {
+		code, got := getLocales(goodModule, "de")
+		if code != http.StatusOK || len(got) != 0 {
+			t.Errorf("de: status=%d body=%v", code, got)
+		}
+	})
+
+	t.Run("UnknownModuleIs404", func(t *testing.T) {
+		if code, _ := getLocales("does-not-exist", "fr"); code != http.StatusNotFound {
+			t.Errorf("status = %d, want 404", code)
+		}
+	})
+
+	t.Run("InvalidEntryIsDroppedAndReported", func(t *testing.T) {
+		code, got := getLocales(badModule, "fr")
+		if code != http.StatusOK {
+			t.Fatalf("status = %d", code)
+		}
+		if len(got) != 1 || got["template.displayName"] != "Jeu de test" {
+			t.Errorf("fr = %v; want only the valid entry", got)
+		}
+
+		envInstance.Eventually(t, 60*time.Second, func() (bool, string) {
+			tmpl, err := envInstance.Dyn.Resource(gameTemplateGVR).Get(ctx, badModule, metav1.GetOptions{})
+			if err != nil {
+				return false, "get template: " + err.Error()
+			}
+			conds, _, _ := unstructured.NestedSlice(tmpl.Object, "status", "conditions")
+			for _, c := range conds {
+				m, ok := c.(map[string]any)
+				if !ok || m["type"] != "LocalesValid" {
+					continue
+				}
+				if m["status"] == "False" && m["reason"] == "InvalidEntries" {
+					return true, ""
+				}
+				return false, "LocalesValid=" + asString(m["status"]) + "/" + asString(m["reason"])
+			}
+			return false, "no LocalesValid condition"
+		})
+
+		// The template is cluster-scoped, so its events land in "default".
+		envInstance.Eventually(t, 60*time.Second, func() (bool, string) {
+			evs, err := envInstance.K8s.CoreV1().Events(metav1.NamespaceAll).List(ctx, metav1.ListOptions{
+				FieldSelector: "involvedObject.name=" + badModule + ",type=Warning",
+			})
+			if err != nil {
+				return false, "list events: " + err.Error()
+			}
+			for _, ev := range evs.Items {
+				if strings.Contains(ev.Message, "fr:") {
+					return true, ""
+				}
+			}
+			return false, "no Warning event naming fr: yet"
+		})
+	})
+}
diff --git a/test/e2e/i18n_problem_json_e2e_test.go b/test/e2e/i18n_problem_json_e2e_test.go
new file mode 100644
index 000000000..8bc28eb69
--- /dev/null
+++ b/test/e2e/i18n_problem_json_e2e_test.go
@@ -0,0 +1,231 @@
+//go:build e2e
+
+package e2e
+
+import (
+	"bytes"
+	"encoding/json"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+)
+
+// i18nProblemAccept is the Accept header a dashboard caller sends to receive
+// the RFC 9457 problem document (with its localizable messageId) instead of
+// the plain-text body.
+const i18nProblemAccept = "application/json, application/problem+json"
+
+// rawDo sends one request through the client's cookie jar, so the session
+// cookie rides along, and returns the status, Content-Type and raw body. It
+// exists because APIClient.Do cannot set an Accept header.
+func rawDo(t *testing.T, cli *APIClient, method, path string, body any, accept string) (int, string, []byte) {
+	t.Helper()
+	var br io.Reader
+	if body != nil {
+		b, err := json.Marshal(body)
+		if err != nil {
+			t.Fatalf("marshal body: %v", err)
+		}
+		br = bytes.NewReader(b)
+	}
+	req, err := http.NewRequestWithContext(t.Context(), method, cli.BaseURL+path, br)
+	if err != nil {
+		t.Fatalf("new request %s %s: %v", method, path, err)
+	}
+	if body != nil {
+		req.Header.Set("Content-Type", "application/json")
+	}
+	if isMutation(method) {
+		req.Header.Set("X-Gameplane-CSRF", cli.CSRF)
+	}
+	if accept != "" {
+		req.Header.Set("Accept", accept)
+	}
+	resp, err := cli.HTTP.Do(req)
+	if err != nil {
+		t.Fatalf("do %s %s: %v", method, path, err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+	raw, err := io.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatalf("read %s %s: %v", method, path, err)
+	}
+	return resp.StatusCode, resp.Header.Get("Content-Type"), raw
+}
+
+// decodeProblemBody decodes an RFC 9457 problem body and fails the test when
+// the Content-Type is not application/problem+json.
+func decodeProblemBody(t *testing.T, label, contentType string, raw []byte) map[string]any {
+	t.Helper()
+	if contentType != "application/problem+json" {
+		t.Fatalf("%s: Content-Type=%q, want application/problem+json (body %q)", label, contentType, string(raw))
+	}
+	var doc map[string]any
+	if err := json.Unmarshal(raw, &doc); err != nil {
+		t.Fatalf("%s: decode problem: %v (body %q)", label, err, string(raw))
+	}
+	return doc
+}
+
+// requireProblemFields asserts the status, messageId and detail of a problem
+// document.
+func requireProblemFields(t *testing.T, label string, doc map[string]any, status int, messageID, detail string) {
+	t.Helper()
+	if doc["status"] != float64(status) {
+		t.Errorf("%s: problem status=%v, want %d", label, doc["status"], status)
+	}
+	if doc["messageId"] != messageID {
+		t.Errorf("%s: messageId=%v, want %q", label, doc["messageId"], messageID)
+	}
+	if doc["detail"] != detail {
+		t.Errorf("%s: detail=%v, want %q", label, doc["detail"], detail)
+	}
+}
+
+// TestAPI_I18n_ProblemJSON checks the content negotiation of the API error
+// responses end to end: a caller that asks for application/problem+json gets
+// a problem document with a registry messageId and args, every other caller
+// keeps the byte-identical plain-text body, and the login error stays
+// identical for unknown users and wrong passwords (FR-030).
+//
+// Budget: one e2e-admin login (to create the user) plus one viewer login and
+// one failed-login pair on the raw client. It runs on the primary cluster.
+func TestAPI_I18n_ProblemJSON(t *testing.T) {
+	t.Parallel()
+
+	envInstance.BootstrapAdmin(t, adminUsername, adminPassword)
+	admin := envInstance.APIClient(t, adminUsername, adminPassword)
+	defer admin.Close()
+
+	username, password, id := envInstance.CreateUser(t, admin, "viewer", "e2e-i18n-pj")
+	t.Cleanup(func() {
+		r, _, _ := admin.Delete("/users/" + id)
+		if r != nil {
+			_ = r.Body.Close()
+		}
+	})
+	viewer := envInstance.APIClient(t, username, password)
+	defer viewer.Close()
+
+	// Forbidden: a plain viewer cannot create a server. The RBAC middleware
+	// rejects the request before the body is read.
+	gs := map[string]any{
+		"apiVersion": "gameplane.local/v1alpha1", "kind": "GameServer",
+		"metadata": map[string]any{"name": "e2e-i18n-denied", "namespace": "gameplane-games"},
+		"spec":     map[string]any{"templateRef": map[string]any{"name": "e2e-i18n-template"}},
+	}
+	status, ct, raw := rawDo(t, viewer, http.MethodPost, "/servers", gs, "")
+	if status != http.StatusForbidden {
+		t.Fatalf("viewer POST /servers (plain): status=%d body=%q", status, string(raw))
+	}
+	if !strings.HasPrefix(ct, "text/plain") || string(raw) != "forbidden\n" {
+		t.Errorf("viewer POST /servers (plain): Content-Type=%q body=%q, want text/plain and \"forbidden\\n\"", ct, string(raw))
+	}
+	for _, accept := range []string{"*/*", "application/problem+json;q=0"} {
+		status, ct, raw = rawDo(t, viewer, http.MethodPost, "/servers", gs, accept)
+		if status != http.StatusForbidden {
+			t.Fatalf("viewer POST /servers (Accept %q): status=%d", accept, status)
+		}
+		if !strings.HasPrefix(ct, "text/plain") || string(raw) != "forbidden\n" {
+			t.Errorf("viewer POST /servers (Accept %q): Content-Type=%q body=%q, want the plain body", accept, ct, string(raw))
+		}
+	}
+	status, ct, raw = rawDo(t, viewer, http.MethodPost, "/servers", gs, i18nProblemAccept)
+	if status != http.StatusForbidden {
+		t.Fatalf("viewer POST /servers (problem): status=%d body=%q", status, string(raw))
+	}
+	doc := decodeProblemBody(t, "viewer POST /servers (problem)", ct, raw)
+	requireProblemFields(t, "viewer POST /servers (problem)", doc, http.StatusForbidden, "server.forbidden", "forbidden")
+	if args, ok := doc["args"].(map[string]any); !ok || len(args) != 0 {
+		t.Errorf("viewer POST /servers (problem): args=%v, want empty object", doc["args"])
+	}
+
+	// Validation: an unsupported notification sink kind is a 422 whose plain
+	// body and problem detail carry the same sentence.
+	notif := map[string]any{"sinks": []any{map[string]any{"name": "x", "kind": "telegram", "enabled": false}}}
+	const notifText = "sinks[0].kind must be one of discord|slack|smtp|webhook|ntfy"
+	status, _, raw = rawDo(t, admin, http.MethodPut, "/admin/config/notifications", notif, "")
+	if status != http.StatusUnprocessableEntity {
+		t.Fatalf("PUT /admin/config/notifications (plain): status=%d body=%q", status, string(raw))
+	}
+	if string(raw) != notifText+"\n" {
+		t.Errorf("PUT /admin/config/notifications (plain): body=%q, want %q", string(raw), notifText+"\n")
+	}
+	status, ct, raw = rawDo(t, admin, http.MethodPut, "/admin/config/notifications", notif, i18nProblemAccept)
+	if status != http.StatusUnprocessableEntity {
+		t.Fatalf("PUT /admin/config/notifications (problem): status=%d body=%q", status, string(raw))
+	}
+	doc = decodeProblemBody(t, "PUT /admin/config/notifications (problem)", ct, raw)
+	requireProblemFields(t, "PUT /admin/config/notifications (problem)", doc, http.StatusUnprocessableEntity, "server.generic.422", notifText)
+
+	// Validation with an argument: an unlisted instance language is a 400
+	// whose problem document carries the language as a message argument.
+	status, _, raw = rawDo(t, admin, http.MethodPut, "/admin/config/i18n", map[string]any{"defaultLanguage": "zz"}, "")
+	if status != http.StatusBadRequest {
+		t.Fatalf("PUT /admin/config/i18n (plain): status=%d body=%q", status, string(raw))
+	}
+	if string(raw) != "language is not available: zz\n" {
+		t.Errorf("PUT /admin/config/i18n (plain): body=%q", string(raw))
+	}
+	status, ct, raw = rawDo(t, admin, http.MethodPut, "/admin/config/i18n", map[string]any{"defaultLanguage": "zz"}, i18nProblemAccept)
+	if status != http.StatusBadRequest {
+		t.Fatalf("PUT /admin/config/i18n (problem): status=%d body=%q", status, string(raw))
+	}
+	doc = decodeProblemBody(t, "PUT /admin/config/i18n (problem)", ct, raw)
+	requireProblemFields(t, "PUT /admin/config/i18n (problem)", doc, http.StatusBadRequest, "server.i18n.unlisted_language", "language is not available: zz")
+	if args, ok := doc["args"].(map[string]any); !ok || args["language"] != "zz" {
+		t.Errorf("PUT /admin/config/i18n (problem): args=%v, want language=zz", doc["args"])
+	}
+
+	// Login privacy (FR-030): an unknown user and a wrong password get the
+	// same problem document, byte for byte. A fresh client without a cookie
+	// jar keeps these attempts out of the viewer's session.
+	rawLogin := func(body string) (int, string, []byte) {
+		req, err := http.NewRequestWithContext(t.Context(), http.MethodPost, viewer.BaseURL+"/auth/login", strings.NewReader(body))
+		if err != nil {
+			t.Fatalf("build login request: %v", err)
+		}
+		req.Header.Set("Content-Type", "application/json")
+		req.Header.Set("Accept", i18nProblemAccept)
+		resp, err := (&http.Client{Timeout: viewer.HTTP.Timeout}).Do(req)
+		if err != nil {
+			t.Fatalf("login do: %v", err)
+		}
+		defer func() { _ = resp.Body.Close() }()
+		b, err := io.ReadAll(resp.Body)
+		if err != nil {
+			t.Fatalf("login read: %v", err)
+		}
+		if resp.StatusCode == http.StatusTooManyRequests {
+			t.Fatalf("login rate limited (429) body=%q", string(b))
+		}
+		return resp.StatusCode, resp.Header.Get("Content-Type"), b
+	}
+	uStatus, uCT, uBody := rawLogin(`{"username":"e2e-i18n-does-not-exist","password":"definitely-not-the-password"}`)
+	wStatus, wCT, wBody := rawLogin(`{"username":"` + username + `","password":"definitely-not-the-password"}`)
+	if uStatus != http.StatusUnauthorized || wStatus != http.StatusUnauthorized {
+		t.Fatalf("login statuses: unknown=%d wrong=%d, want 401 for both", uStatus, wStatus)
+	}
+	uDoc := decodeProblemBody(t, "login unknown user", uCT, uBody)
+	requireProblemFields(t, "login unknown user", uDoc, http.StatusUnauthorized, "server.auth.invalid_credentials", "invalid credentials")
+	wDoc := decodeProblemBody(t, "login wrong password", wCT, wBody)
+	requireProblemFields(t, "login wrong password", wDoc, http.StatusUnauthorized, "server.auth.invalid_credentials", "invalid credentials")
+	if string(uBody) != string(wBody) {
+		t.Fatalf("login error responses differ — enumeration oracle:\n  unknown: %q\n  wrong:   %q", string(uBody), string(wBody))
+	}
+
+	// Unauthenticated: a request with no session cookie gets the generic
+	// unauthenticated text, plain or as a problem document.
+	anon := &APIClient{BaseURL: viewer.BaseURL, HTTP: &http.Client{Timeout: viewer.HTTP.Timeout}}
+	status, _, raw = rawDo(t, anon, http.MethodGet, "/servers", nil, "")
+	if status != http.StatusUnauthorized || string(raw) != "unauthenticated\n" {
+		t.Errorf("anonymous GET /servers (plain): status=%d body=%q, want 401 \"unauthenticated\\n\"", status, string(raw))
+	}
+	status, ct, raw = rawDo(t, anon, http.MethodGet, "/servers", nil, i18nProblemAccept)
+	if status != http.StatusUnauthorized {
+		t.Fatalf("anonymous GET /servers (problem): status=%d body=%q", status, string(raw))
+	}
+	anonDoc := decodeProblemBody(t, "anonymous GET /servers (problem)", ct, raw)
+	requireProblemFields(t, "anonymous GET /servers (problem)", anonDoc, http.StatusUnauthorized, "server.common.unauthenticated", "unauthenticated")
+}
diff --git a/web/Dockerfile b/web/Dockerfile
index 0e847eb2f..9dea835a3 100644
--- a/web/Dockerfile
+++ b/web/Dockerfile
@@ -4,6 +4,16 @@
 # publish/release workflows pass `context: .` and `file: web/Dockerfile`).
 # Everything this stage needs lives under web/, so only web/ is copied in.
 
+# ---- compute the language manifest ----
+# The language listing rule (which locales are shown in pickers) lives in the
+# shared Go checker (i18n/), so the manifest is produced by that checker here
+# rather than re-implemented in TypeScript. Only i18n/ is needed for this stage.
+FROM --platform=$BUILDPLATFORM golang:1.27-alpine AS i18n
+WORKDIR /src
+COPY i18n/ ./i18n/
+WORKDIR /src/i18n
+RUN mkdir -p /out && go build -o /tmp/i18n-check ./cmd/i18n-check && /tmp/i18n-check --manifest /out/languages.json --valid-out /out/valid locales
+
 # ---- build the SPA ----
 FROM node:26-bookworm-slim AS build
 WORKDIR /src/web
@@ -12,7 +22,17 @@ WORKDIR /src/web
 COPY web/package.json web/package-lock.json* ./
 RUN npm ci
 
+# Shared locale catalogs live outside web/; the i18n scripts and Vite alias
+# read them from ../i18n/locales relative to /src/web.
+COPY i18n/locales ../i18n/locales
+# Filtered packs (only entries the checker accepts), written by the i18n stage.
+# The compile script reads them through GAMEPLANE_I18N_VALID, so no Go is needed here.
+COPY --from=i18n /out/valid ../i18n/valid
+ENV GAMEPLANE_I18N_VALID=../i18n/valid
+
 COPY web/ ./
+# Generated language manifest (computed by the i18n stage above).
+COPY --from=i18n /out/languages.json ./src/generated/i18n/languages.json
 # Vite emits to web/dist. tsc + vite build run via `npm run build`.
 RUN npm run build
 
diff --git a/web/Dockerfile.dockerignore b/web/Dockerfile.dockerignore
index 3409dacfb..cf82f41df 100644
--- a/web/Dockerfile.dockerignore
+++ b/web/Dockerfile.dockerignore
@@ -9,7 +9,11 @@
 # local copies must never leak in.
 *
 !web
+!i18n
 web/node_modules
 web/dist
 web/.vite
 web/coverage
+# Locally generated i18n output (fixtures, pseudo-language en-XA) must never
+# reach an image; the build regenerates the catalogs and copies languages.json.
+web/src/generated
diff --git a/web/e2e/specs/api-cache.spec.ts b/web/e2e/specs/api-cache.spec.ts
index 6b14f61be..2063d0944 100644
--- a/web/e2e/specs/api-cache.spec.ts
+++ b/web/e2e/specs/api-cache.spec.ts
@@ -65,7 +65,7 @@ test("API reads bypass a cached HTML document at the same URL", async ({ page, b
         revision,
       });
       expect(jsonRequests).toBe(revision);
-      expect(jsonAccepts[revision - 1]).toBe("application/json");
+      expect(jsonAccepts[revision - 1]).toBe("application/json, application/problem+json");
     }
   } finally {
     server.closeAllConnections();
diff --git a/web/eslint.config.js b/web/eslint.config.js
index d80242eaa..f8281dbc5 100644
--- a/web/eslint.config.js
+++ b/web/eslint.config.js
@@ -11,6 +11,11 @@ import tsParser from "@typescript-eslint/parser";
 import tsPlugin from "@typescript-eslint/eslint-plugin";
 import reactPlugin from "eslint-plugin-react";
 import reactHooksPlugin from "eslint-plugin-react-hooks";
+import formatjs from "eslint-plugin-formatjs";
+
+// Files whose user-facing strings have moved to the i18n runtime. This list
+// grows with each string-migration task and switches to all of src in T058.
+const MIGRATED_I18N_PATHS = ["src/lib/i18n/**/*.{ts,tsx}"];
 
 export default [
   {
@@ -68,4 +73,26 @@ export default [
       react: { version: "detect" },
     },
   },
+  {
+    files: MIGRATED_I18N_PATHS,
+    ignores: ["**/*.test.{ts,tsx}"],
+    plugins: { formatjs },
+    rules: {
+      "formatjs/enforce-description": ["error", "literal"],
+      "formatjs/enforce-placeholders": "error",
+      "formatjs/no-literal-string-in-jsx": [
+        "error",
+        {
+          props: {
+            include: [
+              ["*", "aria-label"],
+              ["*", "title"],
+              ["*", "placeholder"],
+              ["*", "alt"],
+            ],
+          },
+        },
+      ],
+    },
+  },
 ];
diff --git a/web/index.html b/web/index.html
index 5b03ed9ff..e47bdafc3 100644
--- a/web/index.html
+++ b/web/index.html
@@ -109,6 +109,22 @@
         } catch (e) { /* localStorage unavailable — keep the dark default already in markup */ }
       })();
     </script>
+    <script id="i18n-boot">
+      (function () {
+        // Pre-React language boot (spec 019): reuse the language applied last
+        // time so <html lang> is right before the bundle mounts. v1 never lists
+        // right-to-left languages, so dir is always ltr here.
+        try {
+          var raw = window.localStorage.getItem("gameplane-language");
+          if (!raw) return;
+          var applied = JSON.parse(raw).applied;
+          if (typeof applied === "string" && /^[a-z]{2,3}(-[A-Za-z0-9]{2,8})*$/.test(applied)) {
+            document.documentElement.lang = applied;
+            document.documentElement.dir = "ltr";
+          }
+        } catch (e) { /* localStorage unavailable or corrupt — keep the en default */ }
+      })();
+    </script>
     <link rel="preconnect" href="https://fonts.googleapis.com" />
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
     <link
diff --git a/web/package-lock.json b/web/package-lock.json
index 3ee62e162..b75a76648 100644
--- a/web/package-lock.json
+++ b/web/package-lock.json
@@ -25,10 +25,13 @@
         "react-aria": "^3.53.0",
         "react-aria-components": "^1.22.0",
         "react-dom": "^19.3.0",
+        "react-intl": "^12.1.4",
         "tailwind-merge": "^3.7.0"
       },
       "devDependencies": {
         "@eslint/js": "^9.39.5",
+        "@formatjs/cli": "^6.16.34",
+        "@formatjs/icu-messageformat-parser": "^2.11.4",
         "@playwright/test": "^1.64.0",
         "@tailwindcss/postcss": "^4.3.3",
         "@tanstack/router-devtools": "^1.167.2",
@@ -45,6 +48,7 @@
         "@vitest/coverage-v8": "^5.0.3",
         "autoprefixer": "^10.6.1",
         "eslint": "^9.39.5",
+        "eslint-plugin-formatjs": "^8.1.1",
         "eslint-plugin-react": "^7.37.5",
         "eslint-plugin-react-hooks": "^7.1.1",
         "globals": "^17.13.0",
@@ -917,6 +921,140 @@
         }
       }
     },
+    "node_modules/@formatjs/cli": {
+      "version": "6.16.34",
+      "resolved": "https://registry.npmjs.org/@formatjs/cli/-/cli-6.16.34.tgz",
+      "integrity": "sha512-t4ygg5OXhchsrGxozTg++NGIKV9DvLrQnhH5vgukfQdicAHoXXZtfN5MxAUdxoSN4tU8Wu+Rl1iBnShVg7I1TA==",
+      "dev": true,
+      "license": "MIT",
+      "bin": {
+        "formatjs": "bin/formatjs"
+      },
+      "engines": {
+        "node": ">= 20.12.0"
+      },
+      "optionalDependencies": {
+        "@formatjs/cli-native-darwin-arm64": "1.1.28",
+        "@formatjs/cli-native-linux-arm64": "1.2.28",
+        "@formatjs/cli-native-linux-arm64-musl": "1.0.26",
+        "@formatjs/cli-native-linux-x64": "1.1.28",
+        "@formatjs/cli-native-linux-x64-musl": "1.0.26",
+        "@formatjs/cli-native-win32-x64": "1.1.29"
+      },
+      "peerDependencies": {
+        "@glimmer/syntax": "^0.84.3 || ^0.95.0",
+        "@vue/compiler-core": "3",
+        "content-tag": "4",
+        "vue": "3"
+      },
+      "peerDependenciesMeta": {
+        "@glimmer/env": {
+          "optional": true
+        },
+        "@glimmer/reference": {
+          "optional": true
+        },
+        "@glimmer/syntax": {
+          "optional": true
+        },
+        "@glimmer/validator": {
+          "optional": true
+        },
+        "@vue/compiler-core": {
+          "optional": true
+        },
+        "content-tag": {
+          "optional": true
+        },
+        "vue": {
+          "optional": true
+        }
+      }
+    },
+    "node_modules/@formatjs/cli-native-darwin-arm64": {
+      "version": "1.1.28",
+      "resolved": "https://registry.npmjs.org/@formatjs/cli-native-darwin-arm64/-/cli-native-darwin-arm64-1.1.28.tgz",
+      "integrity": "sha512-kFkM6peuJgZrzcuWZiCbnh3o9SHYWBYq3OW8vwL7Cd3IRnzaH1InnzverZpqhLfRKDs+JGa64ll/IuieW/u+4A==",
+      "cpu": [
+        "arm64"
+      ],
+      "dev": true,
+      "license": "MIT",
+      "optional": true,
+      "os": [
+        "darwin"
+      ]
+    },
+    "node_modules/@formatjs/cli-native-linux-arm64": {
+      "version": "1.2.28",
+      "resolved": "https://registry.npmjs.org/@formatjs/cli-native-linux-arm64/-/cli-native-linux-arm64-1.2.28.tgz",
+      "integrity": "sha512-yW8nfFoFJfWvDCbysEH9aU+zDbBPvoNcq1pYs8qoxwXSrvZS8irBdyfuX//Cqz6hQ2/fyGfbL/fxizotX0O4dQ==",
+      "cpu": [
+        "arm64"
+      ],
+      "dev": true,
+      "license": "MIT",
+      "optional": true,
+      "os": [
+        "linux"
+      ]
+    },
+    "node_modules/@formatjs/cli-native-linux-arm64-musl": {
+      "version": "1.0.26",
+      "resolved": "https://registry.npmjs.org/@formatjs/cli-native-linux-arm64-musl/-/cli-native-linux-arm64-musl-1.0.26.tgz",
+      "integrity": "sha512-nJu7scro7jqNJyrsUUD0ui+onpjog54Z8yf5h58Tqbr8kUJeUtmsz/cP4a42yU5WiJW5cXCFsT5nq2a8wM63Xw==",
+      "cpu": [
+        "arm64"
+      ],
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+      "optional": true,
+      "peer": true,
+      "engines": {
+        "node": ">=12"
+      }
+    },
     "node_modules/w3c-xmlserializer": {
       "version": "6.0.0",
       "resolved": "https://registry.npmjs.org/w3c-xmlserializer/-/w3c-xmlserializer-6.0.0.tgz",
diff --git a/web/package.json b/web/package.json
index 96ef9d776..8b97b6203 100644
--- a/web/package.json
+++ b/web/package.json
@@ -5,7 +5,13 @@
   "type": "module",
   "scripts": {
     "dev": "vite",
-    "build": "tsc -b && vite build",
+    "build": "npm run i18n:compile && tsc -b && vite build",
+    "i18n:extract-only": "formatjs extract \"src/**/*.{ts,tsx}\" --ignore \"src/**/*.test.{ts,tsx}\" --ignore \"src/**/*.d.ts\" --ignore \"src/generated/**\" --out-file src/generated/i18n/extracted.json",
+    "i18n:extract": "npm run i18n:extract-only && node scripts/i18n-reference.mjs",
+    "i18n:compile": "node scripts/i18n-compile.mjs",
+    "i18n:fixtures": "node scripts/i18n-fixtures.mjs",
+    "i18n:pseudo": "node scripts/i18n-pseudo.mjs",
+    "i18n:manifest": "cd ../i18n && go run ./cmd/i18n-check --manifest ../web/src/generated/i18n/languages.json locales",
     "preview": "vite preview",
     "lint": "eslint .",
     "test": "vitest run",
@@ -36,10 +42,13 @@
     "react-aria": "^3.53.0",
     "react-aria-components": "^1.22.0",
     "react-dom": "^19.3.0",
+    "react-intl": "^12.1.4",
     "tailwind-merge": "^3.7.0"
   },
   "devDependencies": {
     "@eslint/js": "^9.39.5",
+    "@formatjs/cli": "^6.16.34",
+    "@formatjs/icu-messageformat-parser": "^2.11.4",
     "@playwright/test": "^1.64.0",
     "@tailwindcss/postcss": "^4.3.3",
     "@tanstack/router-devtools": "^1.167.2",
@@ -56,6 +65,7 @@
     "@vitest/coverage-v8": "^5.0.3",
     "autoprefixer": "^10.6.1",
     "eslint": "^9.39.5",
+    "eslint-plugin-formatjs": "^8.1.1",
     "eslint-plugin-react": "^7.37.5",
     "eslint-plugin-react-hooks": "^7.1.1",
     "globals": "^17.13.0",
diff --git a/web/scripts/i18n-compile.mjs b/web/scripts/i18n-compile.mjs
new file mode 100644
index 000000000..6f0f74158
--- /dev/null
+++ b/web/scripts/i18n-compile.mjs
@@ -0,0 +1,58 @@
+// Compiles every shared locale catalog into an AST-format JSON chunk under
+// src/generated/i18n/<tag>.json. The dashboard loads these chunks at runtime
+// via import.meta.glob (src/lib/i18n/languages.ts).
+//
+// Only entries the shared Go checker accepts are compiled (i18n-check
+// --valid-out). Invalid, unknown and missing entries are left out, so the
+// dashboard shows English for them. The filtered packs come from
+// GAMEPLANE_I18N_VALID when a build already has them (the web Docker stage
+// copies them in). Otherwise this script runs the checker to write them to
+// ../i18n/.valid, which needs Go on PATH.
+//
+// Node ESM, no dependencies beyond the local @formatjs/cli binary. Skips
+// silently when the shared locales directory is absent.
+import { execFileSync, spawnSync } from "node:child_process";
+import { existsSync, mkdirSync, readdirSync, rmSync } from "node:fs";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const webRoot = path.resolve(here, "..");
+const localesDir = path.resolve(webRoot, "../i18n/locales");
+const outDir = path.join(webRoot, "src/generated/i18n");
+const formatjsBin = path.join(webRoot, "node_modules/.bin/formatjs");
+const i18nDir = path.resolve(webRoot, "../i18n");
+const generatedValidDir = path.join(i18nDir, ".valid");
+
+if (!existsSync(localesDir)) {
+  process.exit(0);
+}
+
+let validDir = process.env.GAMEPLANE_I18N_VALID ? path.resolve(process.env.GAMEPLANE_I18N_VALID) : "";
+if (validDir === "") {
+  // Exit status 1 means the checker reported findings. Those still come with
+  // the filtered packs, and CI fails on them separately. Other failures stop
+  // the build.
+  rmSync(generatedValidDir, { recursive: true, force: true });
+  const run = spawnSync("go", ["run", "./cmd/i18n-check", "--valid-out", generatedValidDir, "locales"], {
+    cwd: i18nDir,
+    stdio: "inherit",
+  });
+  if (run.error || (run.status !== 0 && run.status !== 1)) {
+    console.error("i18n:compile could not write the filtered language packs");
+    process.exit(1);
+  }
+  validDir = generatedValidDir;
+}
+
+mkdirSync(outDir, { recursive: true });
+
+for (const entry of readdirSync(validDir, { withFileTypes: true })) {
+  if (!entry.isDirectory()) continue;
+  const tag = entry.name;
+  const source = path.join(validDir, tag, "app.json");
+  if (!existsSync(source)) continue;
+  const target = path.join(outDir, `${tag}.json`);
+  execFileSync(formatjsBin, ["compile", source, "--ast", "--out-file", target], { stdio: "inherit" });
+  console.log(`i18n:compile ${tag} -> src/generated/i18n/${tag}.json`);
+}
diff --git a/web/scripts/i18n-fixtures.mjs b/web/scripts/i18n-fixtures.mjs
new file mode 100644
index 000000000..e8e677d6c
--- /dev/null
+++ b/web/scripts/i18n-fixtures.mjs
@@ -0,0 +1,29 @@
+// Writes the fixture language used by the i18n E2E specs (spec 019, T046):
+// a listed language "zz" with 0% completeness and an empty compiled catalog,
+// so the specs can switch languages and see the English fallback text.
+//
+// Run by `npm run i18n:fixtures`, and by vite.config.ts when
+// VITE_I18N_FIXTURES=1. Release builds never run it, so the generated files
+// never exist there and languages.json never contains "zz".
+import { mkdirSync, writeFileSync } from "node:fs";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const outDir = path.resolve(here, "../src/generated/i18n");
+
+const fixtureManifest = [
+  {
+    tag: "zz",
+    nativeName: "Fixture 0%",
+    englishName: "Fixture",
+    direction: "ltr",
+    completeness: 0,
+    listed: true,
+  },
+];
+
+mkdirSync(outDir, { recursive: true });
+writeFileSync(path.join(outDir, "languages.fixtures.json"), `${JSON.stringify(fixtureManifest, null, 2)}\n`);
+writeFileSync(path.join(outDir, "zz.json"), "{}\n");
+console.log("i18n:fixtures wrote languages.fixtures.json and zz.json");
diff --git a/web/scripts/i18n-pseudo-lib.d.mts b/web/scripts/i18n-pseudo-lib.d.mts
new file mode 100644
index 000000000..17fa8c30a
--- /dev/null
+++ b/web/scripts/i18n-pseudo-lib.d.mts
@@ -0,0 +1,19 @@
+import type { MessageFormatElement } from "@formatjs/icu-messageformat-parser";
+
+export const PSEUDO_TAG: string;
+export const LENGTH_FACTOR: number;
+export function accent(text: string): string;
+export function pseudoLiteral(text: string): string;
+export function pseudoLocalizeAst(elements: MessageFormatElement[]): MessageFormatElement[];
+export function pseudoLocalizeMessage(message: string): MessageFormatElement[];
+export function buildPseudoCatalog(
+  reference: Record<string, { defaultMessage: string }>,
+): Record<string, MessageFormatElement[]>;
+export const pseudoManifestEntry: {
+  tag: string;
+  nativeName: string;
+  englishName: string;
+  direction: "ltr" | "rtl";
+  completeness: number;
+  listed: boolean;
+};
diff --git a/web/scripts/i18n-pseudo-lib.mjs b/web/scripts/i18n-pseudo-lib.mjs
new file mode 100644
index 000000000..396659c62
--- /dev/null
+++ b/web/scripts/i18n-pseudo-lib.mjs
@@ -0,0 +1,97 @@
+// Pseudo-localization transform for the en-XA test language (spec 019, T099,
+// FR-038). Pure functions only; scripts/i18n-pseudo.mjs does the file I/O.
+//
+// The transform works on the parsed ICU AST, so placeholders, plural and
+// select syntax, the pound sign and rich-text tags are never touched: only
+// literal text is accented and lengthened.
+import { parse, TYPE } from "@formatjs/icu-messageformat-parser";
+
+const ACCENTS = {
+  a: "á", b: "ƀ", c: "ç", d: "ð", e: "é", f: "ƒ", g: "ĝ", h: "ĥ", i: "í", j: "ĵ",
+  k: "ķ", l: "ļ", m: "ɱ", n: "ñ", o: "ó", p: "þ", q: "ǫ", r: "ŕ", s: "š", t: "ţ",
+  u: "ú", v: "ṽ", w: "ŵ", x: "ẋ", y: "ý", z: "ž",
+  A: "Á", B: "Ɓ", C: "Ç", D: "Ð", E: "É", F: "Ƒ", G: "Ĝ", H: "Ĥ", I: "Í", J: "Ĵ",
+  K: "Ķ", L: "Ļ", M: "Ṁ", N: "Ñ", O: "Ó", P: "Þ", Q: "Ǫ", R: "Ŕ", S: "Š", T: "Ţ",
+  U: "Ú", V: "Ṽ", W: "Ŵ", X: "Ẋ", Y: "Ý", Z: "Ž",
+};
+
+// Padding repeats this cycle so lengthened text stays readable as pseudo text.
+const PADDING = "~·";
+
+export const PSEUDO_TAG = "en-XA";
+export const LENGTH_FACTOR = 0.4;
+
+// accent replaces ASCII letters with accented look-alikes.
+export function accent(text) {
+  let out = "";
+  for (const ch of text) out += ACCENTS[ch] ?? ch;
+  return out;
+}
+
+// pseudoLiteral accents a run of literal text and appends padding so it is
+// about 40% longer. Whitespace-only runs are left alone.
+export function pseudoLiteral(text) {
+  if (text.trim() === "") return text;
+  const extra = Math.ceil([...text].length * LENGTH_FACTOR);
+  let pad = "";
+  for (let i = 0; i < extra; i += 1) pad += PADDING[i % PADDING.length];
+  return accent(text) + pad;
+}
+
+function transformElements(elements) {
+  return elements.map((el) => {
+    switch (el.type) {
+      case TYPE.literal:
+        return { ...el, value: pseudoLiteral(el.value) };
+      case TYPE.tag:
+        return { ...el, children: transformElements(el.children) };
+      case TYPE.plural:
+      case TYPE.select: {
+        const options = {};
+        for (const [key, option] of Object.entries(el.options)) {
+          options[key] = { ...option, value: transformElements(option.value) };
+        }
+        return { ...el, options };
+      }
+      default:
+        return el;
+    }
+  });
+}
+
+// pseudoLocalizeAst returns the pseudo-localized AST for one parsed message,
+// wrapped in square brackets.
+export function pseudoLocalizeAst(elements) {
+  return [
+    { type: TYPE.literal, value: "[" },
+    ...transformElements(elements),
+    { type: TYPE.literal, value: "]" },
+  ];
+}
+
+// pseudoLocalizeMessage parses an ICU message and returns its compiled AST in
+// the same shape `formatjs compile --ast` writes.
+export function pseudoLocalizeMessage(message) {
+  return pseudoLocalizeAst(parse(message));
+}
+
+// buildPseudoCatalog maps every id of the English reference ({id: {defaultMessage}})
+// to its pseudo-localized AST.
+export function buildPseudoCatalog(reference) {
+  const catalog = {};
+  for (const id of Object.keys(reference).sort()) {
+    catalog[id] = pseudoLocalizeMessage(reference[id].defaultMessage);
+  }
+  return catalog;
+}
+
+// pseudoManifestEntry is the language-manifest row merged in only when
+// VITE_I18N_PSEUDO=1.
+export const pseudoManifestEntry = {
+  tag: PSEUDO_TAG,
+  nativeName: "Pseudo",
+  englishName: "Pseudo-locale",
+  direction: "ltr",
+  completeness: 100,
+  listed: true,
+};
diff --git a/web/scripts/i18n-pseudo.mjs b/web/scripts/i18n-pseudo.mjs
new file mode 100644
index 000000000..43560574a
--- /dev/null
+++ b/web/scripts/i18n-pseudo.mjs
@@ -0,0 +1,26 @@
+// Writes the pseudo-language "en-XA" used to spot untranslated or clipped text
+// (spec 019, T099, FR-038): src/generated/i18n/en-XA.json is compiled from the
+// shared English reference with accented, ~40% longer, bracketed text, keeping
+// ICU placeholders, plural/select syntax and rich-text tags untouched. A
+// manifest row is written to languages.pseudo.json, which languages.ts merges
+// the same way as the fixture manifest.
+//
+// Run by `npm run i18n:pseudo`, and by vite.config.ts when VITE_I18N_PSEUDO=1.
+// Release builds never run it, so the generated files never exist there and
+// languages.json never contains "en-XA".
+import { mkdirSync, readFileSync, writeFileSync } from "node:fs";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import { buildPseudoCatalog, pseudoManifestEntry } from "./i18n-pseudo-lib.mjs";
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const outDir = path.resolve(here, "../src/generated/i18n");
+const referencePath = path.resolve(here, "../../i18n/locales/en/app.json");
+
+const reference = JSON.parse(readFileSync(referencePath, "utf8"));
+const catalog = buildPseudoCatalog(reference);
+
+mkdirSync(outDir, { recursive: true });
+writeFileSync(path.join(outDir, "en-XA.json"), `${JSON.stringify(catalog)}\n`);
+writeFileSync(path.join(outDir, "languages.pseudo.json"), `${JSON.stringify([pseudoManifestEntry], null, 2)}\n`);
+console.log(`i18n:pseudo wrote en-XA.json (${Object.keys(catalog).length} messages) and languages.pseudo.json`);
diff --git a/web/scripts/i18n-reference.mjs b/web/scripts/i18n-reference.mjs
new file mode 100644
index 000000000..eea16e875
--- /dev/null
+++ b/web/scripts/i18n-reference.mjs
@@ -0,0 +1,37 @@
+// Builds the extracted-message reference: every message the dashboard source
+// uses (from `formatjs extract`) plus every server.*, condition.* and notify.*
+// entry from the shared English catalog. Written back sorted by key so the
+// output is stable across runs.
+//
+// Node ESM, no dependencies. Run via `npm run i18n:extract`.
+import { readFileSync, writeFileSync } from "node:fs";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const webRoot = path.resolve(here, "..");
+const extractedPath = path.join(webRoot, "src/generated/i18n/extracted.json");
+const referencePath = path.join(webRoot, "../i18n/locales/en/app.json");
+
+const SERVER_PREFIXES = ["server.", "condition.", "notify."];
+
+const extracted = JSON.parse(readFileSync(extractedPath, "utf8"));
+const reference = JSON.parse(readFileSync(referencePath, "utf8"));
+
+const merged = {};
+for (const [id, entry] of Object.entries(reference)) {
+  if (SERVER_PREFIXES.some((prefix) => id.startsWith(prefix))) {
+    merged[id] = entry;
+  }
+}
+for (const [id, entry] of Object.entries(extracted)) {
+  merged[id] = { defaultMessage: entry.defaultMessage, description: entry.description };
+}
+
+const sorted = {};
+for (const key of Object.keys(merged).sort()) {
+  sorted[key] = merged[key];
+}
+
+writeFileSync(extractedPath, JSON.stringify(sorted, null, 2) + "\n");
+console.log(`i18n:extract wrote ${Object.keys(sorted).length} message(s) to src/generated/i18n/extracted.json`);
diff --git a/web/specs.md b/web/specs.md
index b840a44d6..6c94f3e5a 100644
--- a/web/specs.md
+++ b/web/specs.md
@@ -1067,6 +1067,23 @@ Each namespace is an object of typed functions building and fetching URLs:
 - **events.ts** — event severity / reason → display strings
 - **quantity.ts** — parse/format K8s quantities (500m → 0.5, 1Gi → 1073741824 bytes)
 
+## Internationalization (spec 019)
+
+- **Provider.** `src/lib/i18n/I18nProvider.tsx` wraps the whole app inside `QueryClientProvider` in `src/main.tsx`, so `/login` and `/share/*` are covered. It renders react-intl `IntlProvider` and react-aria `I18nProvider` with the same locale, and exposes `useLanguage()` (`language`, `setLanguage`, `direction`). Outside a provider `useLanguage()` and `useFormat()` fall back to English.
+- **App wiring** (`AppI18nProvider`, same file). `src/main.tsx` mounts `AppI18nProvider` rather than the bare provider. It supplies the two server inputs to resolution: the user's saved language, read from the cached `["me"]` profile (`preferences.language`) without starting a fetch, so the route guards stay the only `/users/me` caller and the value updates when that cache entry changes; and the instance default from `GET /auth/locale` (`Auth.locale()`, query key `["auth-locale"]`, `staleTime: Infinity`, no retry). A failed locale request leaves the instance default unset, so resolution falls through to `en`. `Users.setLanguage(tag | null)` (`PUT /users/me/language`) is the write path for the saved choice; the picker that calls it is not yet built.
+- **Resolution order** (`src/lib/i18n/resolve.ts`): user choice, then browser choice (storage), then each `navigator.languages` entry (regional, then base language, so `fr-CA` resolves to `fr`), then the instance default, then `en`. Candidates that are not listed languages are skipped. Listing comes only from the generated manifest.
+- **Storage key.** `localStorage["gameplane-language"]` holds `{choice, applied}`. `choice` is the viewer's pick on this browser; `applied` is the language last rendered. Every access is guarded, and failures mean "no preference".
+- **Boot snippet.** `<script id="i18n-boot">` in `web/index.html` reads `applied` before React mounts and sets `<html lang>` (and `dir="ltr"`). It accepts only tags matching `^[a-z]{2,3}(-[A-Za-z0-9]{2,8})*$`.
+- **Catalogs and generated files.** Messages come from the shared `i18n/locales/<tag>/app.json`. The build writes `src/generated/i18n/` (not committed; ignored by `.gitignore`): `<tag>.json` compiled AST catalogs, `extracted.json` (reference for `formatjs extract`), and `languages.json` (the manifest computed by `i18n/cmd/i18n-check`). A missing message renders its `defaultMessage`, and `MISSING_TRANSLATION` is not logged.
+- **Scripts** (`web/package.json`). `i18n:extract` runs `formatjs extract` and then `scripts/i18n-reference.mjs`. `i18n:compile` runs `scripts/i18n-compile.mjs`. `i18n:manifest` runs `i18n-check --manifest`. `build` runs `i18n:compile` first. Vite and Vitest alias `@i18n` to `../i18n/locales`.
+- **Fixture language (E2E only).** `npm run i18n:fixtures` (`scripts/i18n-fixtures.mjs`) writes `src/generated/i18n/languages.fixtures.json` (one listed row: tag `zz`, nativeName `Fixture 0%`, englishName `Fixture`, `completeness: 0`) and an empty `zz.json` catalog. `languages.ts` merges that manifest into the listing. `vite.config.ts` runs the same script only when `VITE_I18N_FIXTURES=1`. Fixtures are written only on request; release builds never request them, and `src/generated/` is gitignored, so `languages.json` never lists `zz` in a release. The Playwright i18n specs (spec 019 T037) run with the flag set.
+- **Pseudo-language (testing only).** `npm run i18n:pseudo` (`scripts/i18n-pseudo.mjs`, transform in `scripts/i18n-pseudo-lib.mjs`) writes `src/generated/i18n/en-XA.json` and `languages.pseudo.json` (one listed row: tag `en-XA`, nativeName `Pseudo`, ltr). The catalog is compiled from the English reference (`i18n/locales/en/app.json`) by parsing each message with `@formatjs/icu-messageformat-parser` and rewriting only literal text in the AST: letters become accented look-alikes, each literal is padded about 40% longer, and the whole message is wrapped in `[ ]`. Placeholders, plural/select syntax, the pound sign and rich-text tags are never touched. `languages.ts` merges the pseudo manifest like the fixture manifest, and `vite.config.ts` runs the script only when `VITE_I18N_PSEUDO=1` (dev server; the planned Playwright `en-XA` project, T100, will set it too). Release builds never set the flag, `src/generated/` is gitignored, and the Go checker never lists `en-XA` (`pack.Listed` excludes it), so a release `languages.json` never contains it (FR-038). Unit tests: `src/lib/i18n/pseudo.test.ts`.
+- **Docker.** The `web` image builds `languages.json` in a Go stage (`i18n-check`), so the listing rule lives in one place.
+- **API errors.** The client sends `Accept: application/json, application/problem+json`. A problem+json body sets `APIError.messageId`, `args` and `detail`, and keeps `body`/`message` equal to the English `detail`. `serverMessageText` and `useServerMessage` (`src/lib/i18n/serverMessage.ts`) translate a `messageId` when the catalog has it. `errorTextIntl` (`src/lib/errors.ts`) falls back to `errorText`.
+- **Formatting.** `useFormat()` (`src/lib/i18n/format.ts`) provides `date`, `time`, `dateTime`, `number`, `relative`, `list` and `duration`, bound to the active locale. The pure `format*In(locale, …)` helpers are for non-React code. Default options match the old no-argument `toLocale*String()` calls, so English output is unchanged.
+- **Lint.** `eslint-plugin-formatjs` rules apply to `src/lib/i18n/**` (`MIGRATED_I18N_PATHS` in `eslint.config.js`). The list grows with each string migration.
+- **CI.** The `web` job builds the language manifest (`npm run i18n:manifest`), runs `i18n-check` with extraction drift, server-message drift and before/after completeness in the job summary, and self-tests the checker on `i18n/testdata/defective/`. Locally the same checks run as `make check-i18n` (part of `make lint`).
+
 ## Realtime (WebSocket & SSE)
 
 ### WebSocket (`lib/ws.ts`)
diff --git a/web/src/__tests__/i18nBoot.test.ts b/web/src/__tests__/i18nBoot.test.ts
new file mode 100644
index 000000000..0463a59b9
--- /dev/null
+++ b/web/src/__tests__/i18nBoot.test.ts
@@ -0,0 +1,65 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import html from "../../index.html?raw";
+
+const bootScript = /<script id="i18n-boot">([\s\S]*?)<\/script>/.exec(html)?.[1];
+if (!bootScript) throw new Error("i18n boot script not found in index.html");
+
+// The boot script runs against the page's own globals (document, localStorage),
+// which vitest's jsdom environment provides, so it is evaluated directly.
+const runBoot = new Function(bootScript) as () => void;
+
+describe("i18n boot script", () => {
+  beforeEach(() => {
+    document.documentElement.lang = "en";
+    document.documentElement.dir = "ltr";
+    localStorage.clear();
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    localStorage.clear();
+  });
+
+  it("applies the language recorded as applied", () => {
+    localStorage.setItem("gameplane-language", JSON.stringify({ choice: "fr", applied: "fr" }));
+    runBoot();
+    expect(document.documentElement.lang).toBe("fr");
+    expect(document.documentElement.dir).toBe("ltr");
+  });
+
+  it("accepts regional tags", () => {
+    localStorage.setItem("gameplane-language", JSON.stringify({ applied: "pt-BR" }));
+    runBoot();
+    expect(document.documentElement.lang).toBe("pt-BR");
+  });
+
+  it("stays on en when the stored value is not valid JSON", () => {
+    localStorage.setItem("gameplane-language", "{garbage");
+    runBoot();
+    expect(document.documentElement.lang).toBe("en");
+  });
+
+  it("stays on en when the stored value is null or has no applied field", () => {
+    localStorage.setItem("gameplane-language", "null");
+    runBoot();
+    expect(document.documentElement.lang).toBe("en");
+
+    localStorage.setItem("gameplane-language", JSON.stringify({ choice: "fr" }));
+    runBoot();
+    expect(document.documentElement.lang).toBe("en");
+  });
+
+  it("ignores an applied value that is not a language tag", () => {
+    localStorage.setItem("gameplane-language", JSON.stringify({ applied: "<x>" }));
+    runBoot();
+    expect(document.documentElement.lang).toBe("en");
+  });
+
+  it("stays on en when localStorage throws", () => {
+    vi.spyOn(Storage.prototype, "getItem").mockImplementation(() => {
+      throw new Error("blocked");
+    });
+    expect(() => runBoot()).not.toThrow();
+    expect(document.documentElement.lang).toBe("en");
+  });
+});
diff --git a/web/src/components/CaptureWidget.tsx b/web/src/components/CaptureWidget.tsx
index 8e216c8b3..bc5c762ba 100644
--- a/web/src/components/CaptureWidget.tsx
+++ b/web/src/components/CaptureWidget.tsx
@@ -61,6 +61,7 @@ import { CaptureWarningBanner } from "@/components/ui/CaptureWarningBanner";
 import { ErrorBanner } from "@/components/ui/ErrorBanner";
 import { Chip } from "@/components/ui/PhaseChip";
 import { formatBytes, formatRelative } from "@/lib/utils";
+import { useFormat } from "@/lib/i18n/format";
 import type { GameServer, NetworkCapture } from "@/types";
 
 const DEFAULT_RETENTION_SECONDS = 86400; // 24h — FR-007's engineering default, not a legal mandate.
@@ -129,6 +130,7 @@ interface Props {
 }
 
 export function CaptureWidget({ name, ns, gs }: Props) {
+  const fmt = useFormat();
   const { data: me, isLoading: meLoading, error: meError, refetch: refetchMe } = useMe();
   const permissions = useResourcePermissions();
   const canManage = !!me && resourceCan(permissions, "captures:manage");
@@ -406,7 +408,7 @@ export function CaptureWidget({ name, ns, gs }: Props) {
               </div>
             </div>
             <div className="text-xs text-default-500">
-              {(activeCaptureDetails?.packetsWritten ?? activeCapture.packetsWritten).toLocaleString()} packets captured
+              {fmt.number(activeCaptureDetails?.packetsWritten ?? activeCapture.packetsWritten)} packets captured
             </div>
           </CardContent>
         </Card>
@@ -455,7 +457,7 @@ export function CaptureWidget({ name, ns, gs }: Props) {
                             </Chip>
                           </TableCell>
                           <TableCell className="font-mono text-sm">{formatBytes(c.bytesWritten)}</TableCell>
-                          <TableCell className="font-mono text-sm">{c.packetsWritten.toLocaleString()}</TableCell>
+                          <TableCell className="font-mono text-sm">{fmt.number(c.packetsWritten)}</TableCell>
                           <TableCell className="font-mono text-sm text-default-500">
                             {durationBetween(c.startedAt, c.completedAt)}
                           </TableCell>
diff --git a/web/src/components/ui/NotificationsPanel.tsx b/web/src/components/ui/NotificationsPanel.tsx
index 03ddf7f8c..8cf6bfd28 100644
--- a/web/src/components/ui/NotificationsPanel.tsx
+++ b/web/src/components/ui/NotificationsPanel.tsx
@@ -1,4 +1,4 @@
-import { useState, useEffect } from "react";
+import { useState, useEffect, useRef } from "react";
 import type { JSX } from "react";
 import { useQueryClient, type QueryFilters } from "@tanstack/react-query";
 import {
@@ -7,6 +7,7 @@ import {
 } from "@heroui/react";
 import { Bell } from "lucide-react";
 import { openEventStream, queryFilterForKind, type GameplaneEvent } from "@/lib/sse";
+import { useFormat } from "@/lib/i18n/format";
 
 interface Notice {
   id: number;
@@ -36,10 +37,18 @@ function phaseOf(obj: GameplaneEvent["object"] | undefined): string {
  */
 export function NotificationsPanel(): JSX.Element {
   const qc = useQueryClient();
+  const fmt = useFormat();
+  // The SSE stream is opened once per query client; the formatter is read through
+  // a ref so a language change does not tear down and reopen the stream.
+  const fmtRef = useRef(fmt);
   const [notices, setNotices] = useState<Notice[]>([]);
   const [open, setOpen] = useState(false);
   const [unread, setUnread] = useState(0);
 
+  useEffect(() => {
+    fmtRef.current = fmt;
+  }, [fmt]);
+
   useEffect(() => {
     let seq = 0;
     // Coalesce invalidations per query key: a burst of watch events for one
@@ -89,7 +98,7 @@ export function NotificationsPanel(): JSX.Element {
         const notice: Notice = {
           id: seq,
           text: `${verb} ${ev.kind.replace(/s$/, "")} ${name}`.trim(),
-          at: new Date().toLocaleTimeString(),
+          at: fmtRef.current.time(new Date()),
         };
         setNotices((prev) => [notice, ...prev].slice(0, 50));
         setUnread((u) => u + 1);
diff --git a/web/src/lib/api.test.ts b/web/src/lib/api.test.ts
index 19ee0f112..21519dd7e 100644
--- a/web/src/lib/api.test.ts
+++ b/web/src/lib/api.test.ts
@@ -916,3 +916,99 @@ describe("Telemetry notice client", () => {
     await expect(Telemetry.ack("keep")).rejects.toMatchObject({ status: 409 });
   });
 });
+
+describe("api() problem+json errors", () => {
+  const problemBody = {
+    type: "about:blank",
+    status: 409,
+    title: "Conflict",
+    detail: "role \"operator\" already exists",
+    messageId: "server.role.exists",
+    args: { role: "operator", count: 2, nested: { ignored: true } },
+  };
+
+  function problemRes(body: string, status = 409): Response {
+    return new Response(body, {
+      status,
+      headers: { "Content-Type": "application/problem+json" },
+    });
+  }
+
+  it("parses a problem+json body into detail, messageId and args", async () => {
+    fetchMock.mockResolvedValueOnce(problemRes(JSON.stringify(problemBody)));
+    await expect(api("/roles")).rejects.toMatchObject({
+      detail: "role \"operator\" already exists",
+      messageId: "server.role.exists",
+      args: { role: "operator", count: 2 },
+    });
+  });
+
+  it("sets body and message to the detail sentence", async () => {
+    fetchMock.mockResolvedValueOnce(problemRes(JSON.stringify(problemBody)));
+    const err = await api("/roles").catch((e: unknown) => e);
+    expect(err).toBeInstanceOf(APIError);
+    const apiErr = err as APIError;
+    expect(apiErr.body).toBe("role \"operator\" already exists");
+    expect(apiErr.message).toBe("409: role \"operator\" already exists");
+    expect(apiErr.status).toBe(409);
+    expect(apiErr.isHTML).toBe(false);
+  });
+
+  it("leaves messageId and args unset when the body omits them", async () => {
+    fetchMock.mockResolvedValueOnce(problemRes(JSON.stringify({ detail: "plain detail" }), 400));
+    const err = (await api("/roles").catch((e: unknown) => e)) as APIError;
+    expect(err.detail).toBe("plain detail");
+    expect(err.messageId).toBeUndefined();
+    expect(err.args).toBeUndefined();
+    expect(err.message).toBe("400: plain detail");
+  });
+
+  it("falls back to the raw body when problem+json is not valid JSON", async () => {
+    fetchMock.mockResolvedValueOnce(problemRes("not json {", 500));
+    const err = (await api("/roles").catch((e: unknown) => e)) as APIError;
+    expect(err.body).toBe("not json {");
+    expect(err.message).toBe("500: not json {");
+    expect(err.detail).toBeUndefined();
+    expect(err.messageId).toBeUndefined();
+  });
+
+  it("falls back to the raw body when problem+json has no string detail", async () => {
+    fetchMock.mockResolvedValueOnce(problemRes(JSON.stringify({ messageId: "x" }), 422));
+    const err = (await api("/roles").catch((e: unknown) => e)) as APIError;
+    expect(err.body).toBe(JSON.stringify({ messageId: "x" }));
+    expect(err.detail).toBeUndefined();
+  });
+
+  it("ignores a non-object args value", async () => {
+    fetchMock.mockResolvedValueOnce(
+      problemRes(JSON.stringify({ detail: "d", messageId: "m", args: ["a"] }), 400),
+    );
+    const err = (await api("/roles").catch((e: unknown) => e)) as APIError;
+    expect(err.messageId).toBe("m");
+    expect(err.args).toBeUndefined();
+  });
+
+  it("keeps plain text error bodies unchanged", async () => {
+    fetchMock.mockResolvedValueOnce(new Response("boom", { status: 500, headers: { "Content-Type": "text/plain" } }));
+    const err = (await api("/roles").catch((e: unknown) => e)) as APIError;
+    expect(err.body).toBe("boom");
+    expect(err.message).toBe("500: boom");
+    expect(err.detail).toBeUndefined();
+    expect(err.messageId).toBeUndefined();
+    expect(err.args).toBeUndefined();
+  });
+
+  it("sends the problem+json Accept header by default", async () => {
+    fetchMock.mockResolvedValueOnce(jsonRes(200, { ok: true }));
+    await api("/roles");
+    const [, init] = fetchMock.mock.calls[0];
+    expect((init.headers as Record<string, string>).Accept).toBe("application/json, application/problem+json");
+  });
+
+  it("lets opts.headers override the Accept header", async () => {
+    fetchMock.mockResolvedValueOnce(jsonRes(200, { ok: true }));
+    await api("/roles", { headers: { Accept: "text/plain" } });
+    const [, init] = fetchMock.mock.calls[0];
+    expect((init.headers as Record<string, string>).Accept).toBe("text/plain");
+  });
+});
diff --git a/web/src/lib/api.ts b/web/src/lib/api.ts
index bea5f4dfc..6bfe3b10b 100644
--- a/web/src/lib/api.ts
+++ b/web/src/lib/api.ts
@@ -56,19 +56,72 @@ export function csrfHeaders(): Record<string, string> {
   return { [CSRF_HEADER]: csrfToken() };
 }
 
+// ProblemFields is the subset of an RFC 9457 problem+json body the dashboard
+// reads: the English detail plus the stable message identifier and its args.
+interface ProblemFields {
+  detail: string;
+  messageId?: string;
+  args?: Record<string, string | number>;
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null && !Array.isArray(value);
+}
+
+// parseProblem returns the problem fields when the response is an
+// application/problem+json body with a string detail; anything else (other
+// content types, unparsable JSON, missing detail) yields null.
+function parseProblem(body: string, contentType?: string): ProblemFields | null {
+  if (!contentType?.toLowerCase().includes("application/problem+json")) return null;
+  let parsed: unknown;
+  try {
+    parsed = JSON.parse(body);
+  } catch {
+    return null;
+  }
+  if (!isRecord(parsed) || typeof parsed.detail !== "string") return null;
+  const fields: ProblemFields = { detail: parsed.detail };
+  if (typeof parsed.messageId === "string") fields.messageId = parsed.messageId;
+  if (isRecord(parsed.args)) {
+    const args: Record<string, string | number> = {};
+    for (const [key, value] of Object.entries(parsed.args)) {
+      if (typeof value === "string" || typeof value === "number") args[key] = value;
+    }
+    fields.args = args;
+  }
+  return fields;
+}
+
 export class APIError extends Error {
   status: number;
   body: string;
   isHTML: boolean;
   retryAfter: string | null;
+  /** English detail from a problem+json body; undefined for other responses. */
+  detail?: string;
+  /** Stable message identifier (problem+json `messageId`), used for translation. */
+  messageId?: string;
+  /** Interpolation arguments for `messageId` (problem+json `args`). */
+  args?: Record<string, string | number>;
   constructor(status: number, body: string, statusText?: string, contentType?: string, retryAfter: string | null = null) {
     const isHTML = body.trimStart().startsWith("<") || (contentType?.includes("text/html") ?? false);
-    const message = isHTML ? `${status} ${statusText || ""}`.trim() : `${status}: ${body}`;
+    const problem = parseProblem(body, contentType);
+    const message = problem
+      ? `${status}: ${problem.detail}`
+      : isHTML ? `${status} ${statusText || ""}`.trim() : `${status}: ${body}`;
     super(message);
     this.status = status;
     this.body = body;
     this.isHTML = isHTML;
     this.retryAfter = retryAfter;
+    if (problem) {
+      // body carries the English sentence so existing callers that display
+      // err.body keep showing the same text they showed before problem+json.
+      this.body = problem.detail;
+      this.detail = problem.detail;
+      this.messageId = problem.messageId;
+      this.args = problem.args;
+    }
   }
 }
 
@@ -84,7 +137,7 @@ export interface Options {
 export async function api<T>(path: string, opts: Options = {}): Promise<T> {
   const method = opts.method ?? "GET";
   const headers: Record<string, string> = {
-    Accept: "application/json",
+    Accept: "application/json, application/problem+json",
     "Content-Type": "application/json",
     ...(opts.headers ?? {}),
   };
diff --git a/web/src/lib/endpoints.ts b/web/src/lib/endpoints.ts
index 14069f1af..adf52bd0c 100644
--- a/web/src/lib/endpoints.ts
+++ b/web/src/lib/endpoints.ts
@@ -249,6 +249,10 @@ export const Users = {
     api<UserThemePreferences>("/users/me/preferences", { method: "PUT", body }),
   resetPreferences: (body?: UserPreferencesReset) =>
     api<UserThemePreferences>("/users/me/preferences/reset", { method: "POST", body }),
+  // Saved dashboard language (spec 019): a listed BCP 47 tag, or null to clear
+  // the choice and fall back to the browser and instance default.
+  setLanguage: (language: string | null) =>
+    api<void>("/users/me/language", { method: "PUT", body: { language } }),
 };
 
 export interface RoleWrite {
@@ -281,6 +285,8 @@ export const Auth = {
       : "/auth/oidc/start",
   // Public, pre-auth: which login methods are enabled + their labels.
   providers: () => api<LoginProvidersResp>("/auth/providers"),
+  // Public, pre-auth: the instance default language tag only (spec 019).
+  locale: () => api<{ defaultLanguage: string }>("/auth/locale"),
 };
 
 // Managed clientSecret Secrets behind dashboard-added identity providers
@@ -435,6 +441,12 @@ export const Modules = {
     api<Module>(`/modules/${name}`, { method: "PATCH", body: { version } }),
   uninstall: (name: string) =>
     api<void>(`/modules/${name}`, { method: "DELETE" }),
+  // locales returns the module's translated messages for a language as a
+  // flat id -> message map ({} when there are none).
+  locales: (name: string, tag: string) =>
+    api<Record<string, string>>(
+      `/modules/${name}/locales/${encodeURIComponent(tag)}`,
+    ),
 };
 
 // UploadedModule is the parsed-metadata echo from a bundle upload
diff --git a/web/src/lib/endpoints_modules_locales.test.ts b/web/src/lib/endpoints_modules_locales.test.ts
new file mode 100644
index 000000000..d6f216225
--- /dev/null
+++ b/web/src/lib/endpoints_modules_locales.test.ts
@@ -0,0 +1,37 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { Modules } from "./endpoints";
+
+const fetchMock = vi.fn();
+
+beforeEach(() => {
+  vi.stubGlobal("fetch", fetchMock);
+  fetchMock.mockImplementation(
+    async () =>
+      new Response(JSON.stringify({ "template.displayName": "Jeu" }), {
+        status: 200,
+        headers: { "Content-Type": "application/json" },
+      }),
+  );
+});
+
+afterEach(() => {
+  fetchMock.mockReset();
+  vi.unstubAllGlobals();
+});
+
+describe("Modules.locales", () => {
+  it("GETs the module's translations for a tag", async () => {
+    const got = await Modules.locales("mc", "fr");
+    expect(got).toEqual({ "template.displayName": "Jeu" });
+    const call = fetchMock.mock.calls.at(-1);
+    expect(call).toBeDefined();
+    expect(call![0]).toBe("/modules/mc/locales/fr");
+    expect(((call![1] ?? {}) as { method?: string }).method ?? "GET").toBe("GET");
+  });
+
+  it("encodes the tag", async () => {
+    await Modules.locales("mc", "pt BR/x");
+    const call = fetchMock.mock.calls.at(-1);
+    expect(call![0]).toBe("/modules/mc/locales/pt%20BR%2Fx");
+  });
+});
diff --git a/web/src/lib/endpoints_more.test.ts b/web/src/lib/endpoints_more.test.ts
index 1a98a3aee..be0d8fb65 100644
--- a/web/src/lib/endpoints_more.test.ts
+++ b/web/src/lib/endpoints_more.test.ts
@@ -476,3 +476,19 @@ describe("ModRegistries secrets", () => {
     expect(last().init.method).toBe("DELETE");
   });
 });
+
+describe("Language endpoints (spec 019)", () => {
+  it("Users.setLanguage sends a PUT with the tag", async () => {
+    await expectCall(Users.setLanguage("fr"), "/users/me/language", "PUT");
+    expect(last().init.body).toBe(JSON.stringify({ language: "fr" }));
+  });
+
+  it("Users.setLanguage(null) clears the saved choice", async () => {
+    await expectCall(Users.setLanguage(null), "/users/me/language", "PUT");
+    expect(last().init.body).toBe(JSON.stringify({ language: null }));
+  });
+
+  it("Auth.locale reads the public instance default", async () => {
+    await expectCall(Auth.locale(), "/auth/locale");
+  });
+});
diff --git a/web/src/lib/errors.ts b/web/src/lib/errors.ts
index 9d4b8257b..012d553e0 100644
--- a/web/src/lib/errors.ts
+++ b/web/src/lib/errors.ts
@@ -1,4 +1,7 @@
+import type { IntlShape } from "react-intl";
+
 import { APIError } from "@/lib/api";
+import { serverMessageText } from "@/lib/i18n/serverMessage";
 
 // errorText renders an unknown thrown value as a user-facing string,
 // unwrapping the JSON {error|message} body of an APIError when present.
@@ -23,3 +26,9 @@ export function errorTextWithStatus(err: unknown, fallback = "request failed"):
   if (err instanceof APIError) return `${err.status}: ${errorText(err, fallback)}`;
   return errorText(err, fallback);
 }
+
+// errorTextIntl prefers the translated server message (problem+json messageId)
+// when the active catalog has it, and otherwise behaves exactly like errorText.
+export function errorTextIntl(intl: IntlShape, err: unknown, fallback = "request failed"): string {
+  return serverMessageText(intl, err) ?? errorText(err, fallback);
+}
diff --git a/web/src/lib/i18n/AppI18nProvider.test.tsx b/web/src/lib/i18n/AppI18nProvider.test.tsx
new file mode 100644
index 000000000..19ea63b5e
--- /dev/null
+++ b/web/src/lib/i18n/AppI18nProvider.test.tsx
@@ -0,0 +1,127 @@
+import { render, screen, waitFor, act } from "@testing-library/react";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import { Auth } from "@/lib/endpoints";
+import type { User } from "@/types";
+import { AppI18nProvider, useLanguage } from "./I18nProvider";
+
+vi.mock("./languages", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("./languages")>();
+  const fr = {
+    tag: "fr",
+    nativeName: "Français",
+    englishName: "French",
+    direction: "ltr" as const,
+    completeness: 90,
+    listed: true,
+  };
+  return {
+    ...actual,
+    listedLanguages: () => [actual.ENGLISH, fr],
+    loadMessages: vi.fn(() => Promise.resolve(null)),
+  };
+});
+
+function Probe() {
+  const { language } = useLanguage();
+  return <p data-testid="state">{language}</p>;
+}
+
+function user(language: string | null): User {
+  return {
+    id: 1,
+    username: "u",
+    displayName: "U",
+    email: "u@example.test",
+    role: "viewer",
+    preferences: {
+      themeType: "preset",
+      presetId: "pink",
+      appearanceMode: "system",
+      customCssEnabled: false,
+      language,
+    },
+  } as unknown as User;
+}
+
+function renderApp(client: QueryClient) {
+  return render(
+    <QueryClientProvider client={client}>
+      <AppI18nProvider>
+        <Probe />
+      </AppI18nProvider>
+    </QueryClientProvider>,
+  );
+}
+
+function newClient(): QueryClient {
+  return new QueryClient({ defaultOptions: { queries: { retry: false } } });
+}
+
+describe("AppI18nProvider", () => {
+  let localeSpy: ReturnType<typeof vi.spyOn>;
+  const languagesDescriptor = Object.getOwnPropertyDescriptor(window.navigator, "languages");
+
+  beforeEach(() => {
+    window.localStorage.clear();
+    // Keep the browser candidates from matching English before the instance default.
+    Object.defineProperty(window.navigator, "languages", { value: ["xx-YY"], configurable: true });
+    localeSpy = vi.spyOn(Auth, "locale").mockResolvedValue({ defaultLanguage: "en" });
+  });
+
+  afterEach(() => {
+    localeSpy.mockRestore();
+    window.localStorage.clear();
+    if (languagesDescriptor) {
+      Object.defineProperty(window.navigator, "languages", languagesDescriptor);
+    }
+  });
+
+  it("uses the saved user language from the cached profile ahead of the instance default", async () => {
+    const client = newClient();
+    client.setQueryData(["me"], user("fr"));
+    renderApp(client);
+    await waitFor(() => expect(screen.getByTestId("state")).toHaveTextContent("fr"));
+    await waitFor(() => expect(localeSpy).toHaveBeenCalled());
+  });
+
+  it("does not fetch /users/me itself", async () => {
+    const client = newClient();
+    const fetchSpy = vi.spyOn(client, "fetchQuery");
+    renderApp(client);
+    await waitFor(() => expect(localeSpy).toHaveBeenCalled());
+    expect(fetchSpy).not.toHaveBeenCalledWith(expect.objectContaining({ queryKey: ["me"] }));
+    expect(client.getQueryData(["me"])).toBeUndefined();
+  });
+
+  it("falls back to the instance default when the user has no saved language", async () => {
+    localeSpy.mockResolvedValue({ defaultLanguage: "fr" });
+    const client = newClient();
+    client.setQueryData(["me"], user(null));
+    renderApp(client);
+    await waitFor(() => expect(screen.getByTestId("state")).toHaveTextContent("fr"));
+  });
+
+  it("falls back to English when the locale request fails", async () => {
+    localeSpy.mockRejectedValue(new Error("network down"));
+    renderApp(newClient());
+    await waitFor(() => expect(localeSpy).toHaveBeenCalled());
+    await act(async () => {
+      await new Promise((resolve) => setTimeout(resolve, 0));
+    });
+    expect(screen.getByTestId("state")).toHaveTextContent("en");
+  });
+
+  it("re-resolves when the cached profile gains a saved language", async () => {
+    localeSpy.mockResolvedValue({ defaultLanguage: "en" });
+    const client = newClient();
+    renderApp(client);
+    await waitFor(() => expect(localeSpy).toHaveBeenCalled());
+    expect(screen.getByTestId("state")).toHaveTextContent("en");
+    act(() => {
+      client.setQueryData(["me"], user("fr"));
+    });
+    await waitFor(() => expect(screen.getByTestId("state")).toHaveTextContent("fr"));
+  });
+});
diff --git a/web/src/lib/i18n/I18nProvider.test.tsx b/web/src/lib/i18n/I18nProvider.test.tsx
new file mode 100644
index 000000000..c8793669a
--- /dev/null
+++ b/web/src/lib/i18n/I18nProvider.test.tsx
@@ -0,0 +1,228 @@
+import { act, fireEvent, render, screen, waitFor } from "@testing-library/react";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { MessageFormatError, ReactIntlError, ReactIntlErrorCode, useIntl } from "react-intl";
+
+import { I18nProvider, onIntlError, useLanguage } from "./I18nProvider";
+import { loadMessages } from "./languages";
+import type { CompiledCatalog } from "./languages";
+
+vi.mock("./languages", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("./languages")>();
+  const fr = {
+    tag: "fr",
+    nativeName: "Français",
+    englishName: "French",
+    direction: "ltr" as const,
+    completeness: 90,
+    listed: true,
+  };
+  const catalogs: Record<string, CompiledCatalog> = {
+    fr: { "greeting.hello": [{ type: 0, value: "Bonjour" }] },
+  };
+  return {
+    ...actual,
+    listedLanguages: () => [actual.ENGLISH, fr],
+    loadMessages: vi.fn((tag: string) => Promise.resolve(catalogs[tag] ?? null)),
+  };
+});
+
+// Probe renders what a stateful consumer sees: the resolved language, a translated
+// and a missing-translation message, a text input, and buttons to change language.
+function Probe() {
+  const { language, setLanguage, direction } = useLanguage();
+  const intl = useIntl();
+  return (
+    <div>
+      <p data-testid="state">{`${language}/${direction}`}</p>
+      <p>{intl.formatMessage({ id: "greeting.hello", defaultMessage: "Hello" })}</p>
+      <p>{intl.formatMessage({ id: "missing.key", defaultMessage: "Fallback text" })}</p>
+      <input aria-label="name" />
+      <button type="button" onClick={() => setLanguage("fr")}>
+        choose fr
+      </button>
+      <button type="button" onClick={() => setLanguage(null)}>
+        auto
+      </button>
+    </div>
+  );
+}
+
+describe("I18nProvider", () => {
+  beforeEach(() => {
+    window.localStorage.clear();
+    document.documentElement.lang = "en";
+    document.documentElement.dir = "ltr";
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    window.localStorage.clear();
+  });
+
+  it("renders children with English defaults and sets the document language", async () => {
+    render(
+      <I18nProvider>
+        <Probe />
+      </I18nProvider>,
+    );
+    expect(screen.getByTestId("state")).toHaveTextContent("en/ltr");
+    expect(screen.getByText("Hello")).toBeInTheDocument();
+    await waitFor(() => expect(window.localStorage.getItem("gameplane-language")).toContain('"applied":"en"'));
+    expect(document.documentElement.lang).toBe("en");
+    expect(document.documentElement.dir).toBe("ltr");
+  });
+
+  it("switches language without unmounting a stateful child", async () => {
+    render(
+      <I18nProvider>
+        <Probe />
+      </I18nProvider>,
+    );
+    const input = screen.getByLabelText("name");
+    fireEvent.change(input, { target: { value: "typed" } });
+
+    fireEvent.click(screen.getByRole("button", { name: "choose fr" }));
+
+    await waitFor(() => expect(document.documentElement.lang).toBe("fr"));
+    expect(screen.getByLabelText("name")).toBe(input);
+    expect(input).toHaveValue("typed");
+    await waitFor(() => expect(screen.getByText("Bonjour")).toBeInTheDocument());
+    expect(screen.getByTestId("state")).toHaveTextContent("fr/ltr");
+  });
+
+  it("renders the defaultMessage when the catalog lacks the id (FR-008)", async () => {
+    render(
+      <I18nProvider>
+        <Probe />
+      </I18nProvider>,
+    );
+    fireEvent.click(screen.getByRole("button", { name: "choose fr" }));
+    await waitFor(() => expect(screen.getByText("Bonjour")).toBeInTheDocument());
+    expect(screen.getByText("Fallback text")).toBeInTheDocument();
+  });
+
+  it("writes the applied language to storage after a change", async () => {
+    render(
+      <I18nProvider>
+        <Probe />
+      </I18nProvider>,
+    );
+    fireEvent.click(screen.getByRole("button", { name: "choose fr" }));
+    await waitFor(() => expect(window.localStorage.getItem("gameplane-language")).toContain('"applied":"fr"'));
+    expect(window.localStorage.getItem("gameplane-language")).toContain('"choice":"fr"');
+  });
+
+  it("returns to automatic resolution when the choice is cleared", async () => {
+    render(
+      <I18nProvider>
+        <Probe />
+      </I18nProvider>,
+    );
+    fireEvent.click(screen.getByRole("button", { name: "choose fr" }));
+    await waitFor(() => expect(document.documentElement.lang).toBe("fr"));
+    fireEvent.click(screen.getByRole("button", { name: "auto" }));
+    await waitFor(() => expect(document.documentElement.lang).toBe("en"));
+    expect(window.localStorage.getItem("gameplane-language")).toContain('"choice":null');
+  });
+
+  it("uses the user language from the account ahead of storage", async () => {
+    window.localStorage.setItem("gameplane-language", JSON.stringify({ choice: "fr", applied: "fr" }));
+    render(
+      <I18nProvider userLanguage="en">
+        <Probe />
+      </I18nProvider>,
+    );
+    expect(screen.getByTestId("state")).toHaveTextContent("en/ltr");
+  });
+
+  it("applies the stored browser choice on mount", async () => {
+    window.localStorage.setItem("gameplane-language", JSON.stringify({ choice: "fr", applied: "en" }));
+    render(
+      <I18nProvider>
+        <Probe />
+      </I18nProvider>,
+    );
+    await waitFor(() => expect(document.documentElement.lang).toBe("fr"));
+    await waitFor(() => expect(screen.getByText("Bonjour")).toBeInTheDocument());
+  });
+
+  it("keeps rendering with English when a catalog fails to load", async () => {
+    render(
+      <I18nProvider>
+        <Probe />
+      </I18nProvider>,
+    );
+    // Arm the one-shot failure only after the initial "en" load, so it is consumed by "fr".
+    await waitFor(() => expect(loadMessages).toHaveBeenCalledWith("en"));
+    vi.mocked(loadMessages).mockImplementationOnce(() => Promise.reject(new Error("chunk failed")));
+    fireEvent.click(screen.getByRole("button", { name: "choose fr" }));
+    await waitFor(() => expect(loadMessages).toHaveBeenCalledWith("fr"));
+    // Flush the rejection through the provider's catch handler.
+    await act(async () => {
+      await new Promise((resolve) => setTimeout(resolve, 0));
+    });
+    expect(document.documentElement.lang).toBe("fr");
+    expect(screen.queryByText("Bonjour")).toBeNull();
+    expect(screen.getByText("Hello")).toBeInTheDocument();
+    expect(screen.getByLabelText("name")).toBeInTheDocument();
+  });
+
+  it("ignores a catalog that resolves after the language moved on", async () => {
+    let resolveFr: (value: CompiledCatalog | null) => void = () => {};
+    render(
+      <I18nProvider>
+        <Probe />
+      </I18nProvider>,
+    );
+    // Arm the pending "fr" load only after the initial "en" load has been requested.
+    await waitFor(() => expect(loadMessages).toHaveBeenCalledWith("en"));
+    vi.mocked(loadMessages).mockImplementationOnce(
+      () => new Promise<CompiledCatalog | null>((resolve) => (resolveFr = resolve)),
+    );
+    fireEvent.click(screen.getByRole("button", { name: "choose fr" }));
+    await waitFor(() => expect(loadMessages).toHaveBeenCalledWith("fr"));
+    fireEvent.click(screen.getByRole("button", { name: "auto" }));
+    await waitFor(() => expect(loadMessages).toHaveBeenLastCalledWith("en"));
+    // The stale "fr" catalog resolves after the cancelled effect; it must be ignored.
+    await act(async () => {
+      resolveFr({ "greeting.hello": [{ type: 0, value: "Bonjour" }] });
+      await new Promise((resolve) => setTimeout(resolve, 0));
+    });
+    expect(screen.getByText("Hello")).toBeInTheDocument();
+    expect(screen.queryByText("Bonjour")).not.toBeInTheDocument();
+  });
+
+  it("uses the English fallback outside a provider", () => {
+    function Outside() {
+      const { language, direction, setLanguage } = useLanguage();
+      return (
+        <button type="button" onClick={() => setLanguage("fr")}>
+          {`${language}:${direction}`}
+        </button>
+      );
+    }
+    render(<Outside />);
+    // setLanguage is a no-op outside a provider: the page stays English.
+    fireEvent.click(screen.getByRole("button", { name: "en:ltr" }));
+    expect(screen.getByRole("button", { name: "en:ltr" })).toBeInTheDocument();
+    expect(document.documentElement.lang).toBe("en");
+  });
+});
+
+describe("onIntlError", () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it("ignores missing translations", () => {
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+    onIntlError(new ReactIntlError(ReactIntlErrorCode.MISSING_TRANSLATION, "missing"));
+    expect(warn).not.toHaveBeenCalled();
+  });
+
+  it("warns for other errors in development", () => {
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+    onIntlError(new MessageFormatError("boom", "fr"));
+    expect(warn).toHaveBeenCalledOnce();
+  });
+});
diff --git a/web/src/lib/i18n/I18nProvider.tsx b/web/src/lib/i18n/I18nProvider.tsx
new file mode 100644
index 000000000..6f23a26ba
--- /dev/null
+++ b/web/src/lib/i18n/I18nProvider.tsx
@@ -0,0 +1,144 @@
+import { createContext, useCallback, useContext, useEffect, useMemo, useState, useSyncExternalStore } from "react";
+import type { ReactNode } from "react";
+import { useQuery, useQueryClient } from "@tanstack/react-query";
+import { IntlProvider, ReactIntlErrorCode } from "react-intl";
+import type { IntlConfig } from "react-intl";
+import { I18nProvider as AriaI18nProvider } from "@react-aria/i18n";
+
+import { Auth } from "@/lib/endpoints";
+import type { User } from "@/types";
+import { directionFor, listedLanguages, loadMessages } from "./languages";
+import type { CompiledCatalog } from "./languages";
+import { resolveLanguage } from "./resolve";
+import { readLanguageStorage, writeLanguageStorage } from "./storage";
+
+export interface I18nContextValue {
+  language: string;
+  setLanguage: (tag: string | null) => void;
+  direction: "ltr" | "rtl";
+}
+
+// Outside a provider (tests, isolated renders) the dashboard stays English.
+const FALLBACK: I18nContextValue = {
+  language: "en",
+  setLanguage: () => {},
+  direction: "ltr",
+};
+
+const I18nContext = createContext<I18nContextValue | null>(null);
+
+export function useLanguage(): I18nContextValue {
+  return useContext(I18nContext) ?? FALLBACK;
+}
+
+// onIntlError keeps the console quiet: missing translations are expected (react-intl
+// falls back to defaultMessage), and other formatting problems are only worth a
+// warning while developing.
+// IntlErrorArg is the union react-intl passes to onError (the IntlError subclasses).
+type IntlErrorArg = Parameters<NonNullable<IntlConfig["onError"]>>[0];
+
+export function onIntlError(err: IntlErrorArg): void {
+  if (err.code === ReactIntlErrorCode.MISSING_TRANSLATION) return;
+  if (import.meta.env.DEV) console.warn(err);
+}
+
+export interface I18nProviderProps {
+  children: ReactNode;
+  userLanguage?: string | null;
+  instanceDefault?: string | null;
+}
+
+interface LoadedMessages {
+  tag: string;
+  messages: CompiledCatalog;
+}
+
+export function I18nProvider({ children, userLanguage, instanceDefault }: I18nProviderProps) {
+  const [choice, setChoice] = useState<string | null>(() => readLanguageStorage().choice);
+  const listed = useMemo(() => listedLanguages().map((row) => row.tag), []);
+
+  const language = resolveLanguage({
+    userChoice: userLanguage,
+    browserChoice: choice,
+    navigatorLanguages: navigator.languages,
+    instanceDefault,
+    listed,
+  });
+  const direction = directionFor(language);
+
+  const [loaded, setLoaded] = useState<LoadedMessages>({ tag: "en", messages: {} });
+
+  useEffect(() => {
+    let cancelled = false;
+    void loadMessages(language)
+      .then((messages) => {
+        if (!cancelled) setLoaded({ tag: language, messages: messages ?? {} });
+      })
+      .catch(() => {
+        // A failed chunk leaves the English defaultMessage text in place.
+        if (!cancelled) setLoaded({ tag: language, messages: {} });
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, [language]);
+
+  useEffect(() => {
+    document.documentElement.lang = language;
+    document.documentElement.dir = direction;
+    writeLanguageStorage({ applied: language });
+  }, [language, direction]);
+
+  const setLanguage = useCallback((tag: string | null) => {
+    writeLanguageStorage({ choice: tag });
+    setChoice(tag);
+  }, []);
+
+  const value = useMemo<I18nContextValue>(
+    () => ({ language, setLanguage, direction }),
+    [language, setLanguage, direction],
+  );
+
+  // Children are never remounted on a language change: while the new catalog
+  // loads, the previous messages stay in place.
+  return (
+    <I18nContext.Provider value={value}>
+      <IntlProvider locale={language} defaultLocale="en" messages={loaded.messages} onError={onIntlError}>
+        <AriaI18nProvider locale={language}>{children}</AriaI18nProvider>
+      </IntlProvider>
+    </I18nContext.Provider>
+  );
+}
+
+// useCachedUserLanguage returns the saved language on the cached ["me"]
+// profile. It only observes the query cache and never starts a fetch: the
+// route guards own /users/me, and this hook re-renders when that cache entry
+// changes (login, a later language picker invalidating ["me"]).
+function useCachedUserLanguage(): string | null | undefined {
+  const queryClient = useQueryClient();
+  const cache = queryClient.getQueryCache();
+  const subscribe = useCallback((onChange: () => void) => cache.subscribe(onChange), [cache]);
+  const snapshot = () => queryClient.getQueryData<User>(["me"])?.preferences?.language;
+  return useSyncExternalStore(subscribe, snapshot, snapshot);
+}
+
+// AppI18nProvider feeds I18nProvider the two server-side inputs of the
+// resolution order (spec 019, FR-004): the signed-in user's saved language
+// from /users/me (cache only), and the instance default from /auth/locale.
+// The locale request is public and cached for the session; a failure leaves
+// the instance default unset, so resolution falls through to English.
+export function AppI18nProvider({ children }: { children: ReactNode }) {
+  const userLanguage = useCachedUserLanguage();
+  const locale = useQuery({
+    queryKey: ["auth-locale"],
+    queryFn: () => Auth.locale(),
+    staleTime: Infinity,
+    retry: false,
+  });
+  const instanceDefault = locale.data?.defaultLanguage;
+  return (
+    <I18nProvider userLanguage={userLanguage} instanceDefault={instanceDefault}>
+      {children}
+    </I18nProvider>
+  );
+}
diff --git a/web/src/lib/i18n/format.test.tsx b/web/src/lib/i18n/format.test.tsx
new file mode 100644
index 000000000..64e51524b
--- /dev/null
+++ b/web/src/lib/i18n/format.test.tsx
@@ -0,0 +1,146 @@
+import { render, screen } from "@testing-library/react";
+import { describe, expect, it } from "vitest";
+import { IntlProvider } from "react-intl";
+
+import {
+  formatDateIn,
+  formatDateTimeIn,
+  formatDurationIn,
+  formatListIn,
+  formatNumberIn,
+  formatRelativeIn,
+  formatTimeIn,
+  makeFormat,
+  useFormat,
+} from "./format";
+
+// Dates are compared against Intl output rather than literal strings so the
+// tests do not depend on the ICU data version of the runner.
+const when = new Date(2026, 0, 15, 14, 5, 9);
+
+describe("pure format helpers", () => {
+  it("formats dates with the default options in en and fr", () => {
+    expect(formatDateIn("en", when)).toBe(
+      new Intl.DateTimeFormat("en", { year: "numeric", month: "numeric", day: "numeric" }).format(when),
+    );
+    expect(formatDateIn("fr", when)).toBe(
+      new Intl.DateTimeFormat("fr", { year: "numeric", month: "numeric", day: "numeric" }).format(when),
+    );
+  });
+
+  it("uses explicit date options when given", () => {
+    const options: Intl.DateTimeFormatOptions = { dateStyle: "long" };
+    expect(formatDateIn("en", when, options)).toBe(new Intl.DateTimeFormat("en", options).format(when));
+  });
+
+  it("formats times with the default options and accepts epoch numbers", () => {
+    const expected = new Intl.DateTimeFormat("en", { hour: "numeric", minute: "2-digit", second: "2-digit" }).format(
+      when,
+    );
+    expect(formatTimeIn("en", when)).toBe(expected);
+    expect(formatTimeIn("en", when.getTime())).toBe(expected);
+    expect(formatTimeIn("fr", when)).toBe(
+      new Intl.DateTimeFormat("fr", { hour: "numeric", minute: "2-digit", second: "2-digit" }).format(when),
+    );
+  });
+
+  it("formats combined date and time in both locales", () => {
+    const enDefault = formatDateTimeIn("en", when);
+    expect(enDefault).toContain(formatDateIn("en", when));
+    expect(enDefault).toContain(formatTimeIn("en", when));
+    expect(formatDateTimeIn("fr", when, { dateStyle: "short" })).toBe(
+      new Intl.DateTimeFormat("fr", { dateStyle: "short" }).format(when),
+    );
+  });
+
+  it("formats numbers in en and fr", () => {
+    expect(formatNumberIn("en", 1234567)).toBe(new Intl.NumberFormat("en").format(1234567));
+    expect(formatNumberIn("fr", 1234567)).toBe(new Intl.NumberFormat("fr").format(1234567));
+    expect(formatNumberIn("en", 1234, { notation: "compact" })).toBe(
+      new Intl.NumberFormat("en", { notation: "compact" }).format(1234),
+    );
+  });
+
+  it("formats relative time", () => {
+    expect(formatRelativeIn("en", -3, "hour")).toBe(new Intl.RelativeTimeFormat("en").format(-3, "hour"));
+    expect(formatRelativeIn("fr", 2, "day")).toBe(new Intl.RelativeTimeFormat("fr").format(2, "day"));
+  });
+
+  it("formats lists in en and fr", () => {
+    expect(formatListIn("en", ["a", "b", "c"])).toBe(new Intl.ListFormat("en").format(["a", "b", "c"]));
+    expect(formatListIn("fr", ["a", "b"], { type: "disjunction" })).toBe(
+      new Intl.ListFormat("fr", { type: "disjunction" }).format(["a", "b"]),
+    );
+  });
+
+  it("formats durations as unit parts and drops zero leading units", () => {
+    const unitOf = (locale: string, amount: number, unit: "hour" | "minute" | "second") =>
+      new Intl.NumberFormat(locale, { style: "unit", unit, unitDisplay: "short" }).format(amount);
+    const enHour = unitOf("en", 1, "hour");
+    const enMinute = unitOf("en", 5, "minute");
+    expect(formatDurationIn("en", 3900)).toBe(
+      new Intl.ListFormat("en", { style: "long", type: "unit" }).format([enHour, enMinute]),
+    );
+    expect(formatDurationIn("en", 0)).toBe(unitOf("en", 0, "second"));
+    expect(formatDurationIn("en", 45)).toBe(unitOf("en", 45, "second"));
+    expect(formatDurationIn("en", 120)).toBe(
+      new Intl.ListFormat("en", { style: "long", type: "unit" }).format([unitOf("en", 2, "minute")]),
+    );
+    expect(formatDurationIn("fr", 3600)).toBe(
+      new Intl.ListFormat("fr", { style: "long", type: "unit" }).format([unitOf("fr", 1, "hour")]),
+    );
+  });
+
+  it("clamps invalid durations to zero seconds", () => {
+    expect(formatDurationIn("en", -5)).toBe(formatDurationIn("en", 0));
+    expect(formatDurationIn("en", Number.NaN)).toBe(formatDurationIn("en", 0));
+    expect(formatDurationIn("en", Number.POSITIVE_INFINITY)).toBe(formatDurationIn("en", 0));
+  });
+});
+
+describe("makeFormat", () => {
+  it("binds the helpers to one locale", () => {
+    const fmt = makeFormat("fr");
+    expect(fmt.number(1000)).toBe(formatNumberIn("fr", 1000));
+    expect(fmt.date(when)).toBe(formatDateIn("fr", when));
+    expect(fmt.time(when)).toBe(formatTimeIn("fr", when));
+    expect(fmt.dateTime(when)).toBe(formatDateTimeIn("fr", when));
+    expect(fmt.relative(1, "week")).toBe(formatRelativeIn("fr", 1, "week"));
+    expect(fmt.list(["x", "y"])).toBe(formatListIn("fr", ["x", "y"]));
+    expect(fmt.duration(90)).toBe(formatDurationIn("fr", 90));
+  });
+
+  it("passes options through to the helpers", () => {
+    const fmt = makeFormat("en");
+    expect(fmt.number(0.5, { style: "percent" })).toBe(formatNumberIn("en", 0.5, { style: "percent" }));
+    expect(fmt.dateTime(when, { dateStyle: "medium" })).toBe(
+      formatDateTimeIn("en", when, { dateStyle: "medium" }),
+    );
+    expect(fmt.time(when, { hour: "2-digit" })).toBe(formatTimeIn("en", when, { hour: "2-digit" }));
+    expect(fmt.date(when, { month: "long" })).toBe(formatDateIn("en", when, { month: "long" }));
+    expect(fmt.list(["x", "y"], { type: "disjunction" })).toBe(
+      formatListIn("en", ["x", "y"], { type: "disjunction" }),
+    );
+  });
+});
+
+describe("useFormat", () => {
+  function Stamp() {
+    const fmt = useFormat();
+    return <p>{fmt.date(when, { dateStyle: "long" })}</p>;
+  }
+
+  it("uses the English fallback outside an IntlProvider", () => {
+    render(<Stamp />);
+    expect(screen.getByText(formatDateIn("en", when, { dateStyle: "long" }))).toBeInTheDocument();
+  });
+
+  it("follows the locale of the surrounding IntlProvider", () => {
+    render(
+      <IntlProvider locale="fr" defaultLocale="en" messages={{}}>
+        <Stamp />
+      </IntlProvider>,
+    );
+    expect(screen.getByText(formatDateIn("fr", when, { dateStyle: "long" }))).toBeInTheDocument();
+  });
+});
diff --git a/web/src/lib/i18n/format.ts b/web/src/lib/i18n/format.ts
new file mode 100644
index 000000000..96d5d9cb3
--- /dev/null
+++ b/web/src/lib/i18n/format.ts
@@ -0,0 +1,93 @@
+import { useContext, useMemo } from "react";
+import { IntlContext, createIntl } from "react-intl";
+import type { IntlShape } from "react-intl";
+
+import { onIntlError } from "./I18nProvider";
+
+// Locale-aware formatting (spec 019, FR-006). The pure helpers take a locale so
+// non-React code can call them; useFormat() binds them to the active locale.
+// Default options reproduce Date/Number toLocale*String() with no arguments, so
+// English output does not change.
+
+const DATE_DEFAULT: Intl.DateTimeFormatOptions = { year: "numeric", month: "numeric", day: "numeric" };
+const TIME_DEFAULT: Intl.DateTimeFormatOptions = { hour: "numeric", minute: "2-digit", second: "2-digit" };
+const DATE_TIME_DEFAULT: Intl.DateTimeFormatOptions = { ...DATE_DEFAULT, ...TIME_DEFAULT };
+
+export function formatDateIn(locale: string, value: Date | number, options?: Intl.DateTimeFormatOptions): string {
+  return new Intl.DateTimeFormat(locale, options ?? DATE_DEFAULT).format(value);
+}
+
+export function formatTimeIn(locale: string, value: Date | number, options?: Intl.DateTimeFormatOptions): string {
+  return new Intl.DateTimeFormat(locale, options ?? TIME_DEFAULT).format(value);
+}
+
+export function formatDateTimeIn(locale: string, value: Date | number, options?: Intl.DateTimeFormatOptions): string {
+  return new Intl.DateTimeFormat(locale, options ?? DATE_TIME_DEFAULT).format(value);
+}
+
+export function formatNumberIn(locale: string, value: number, options?: Intl.NumberFormatOptions): string {
+  return new Intl.NumberFormat(locale, options).format(value);
+}
+
+export function formatRelativeIn(locale: string, value: number, unit: Intl.RelativeTimeFormatUnit): string {
+  return new Intl.RelativeTimeFormat(locale).format(value, unit);
+}
+
+export function formatListIn(locale: string, items: readonly string[], options?: Intl.ListFormatOptions): string {
+  return new Intl.ListFormat(locale, options).format(items);
+}
+
+// formatDurationIn renders seconds as unit parts, e.g. 3900 -> "1 hr, 5 min".
+// Zero-valued leading units are dropped; zero seconds render as "0 sec".
+export function formatDurationIn(locale: string, seconds: number): string {
+  const total = Number.isFinite(seconds) ? Math.max(0, Math.round(seconds)) : 0;
+  const hours = Math.floor(total / 3600);
+  const minutes = Math.floor((total % 3600) / 60);
+  const secs = total % 60;
+  const unit = (amount: number, name: "hour" | "minute" | "second"): string =>
+    formatNumberIn(locale, amount, { style: "unit", unit: name, unitDisplay: "short" });
+  const parts: string[] = [];
+  if (hours > 0) parts.push(unit(hours, "hour"));
+  if (minutes > 0) parts.push(unit(minutes, "minute"));
+  if (secs > 0 || parts.length === 0) parts.push(unit(secs, "second"));
+  return formatListIn(locale, parts, { style: "long", type: "unit" });
+}
+
+export interface FormatApi {
+  date: (value: Date | number, options?: Intl.DateTimeFormatOptions) => string;
+  time: (value: Date | number, options?: Intl.DateTimeFormatOptions) => string;
+  dateTime: (value: Date | number, options?: Intl.DateTimeFormatOptions) => string;
+  number: (value: number, options?: Intl.NumberFormatOptions) => string;
+  relative: (value: number, unit: Intl.RelativeTimeFormatUnit) => string;
+  list: (items: readonly string[], options?: Intl.ListFormatOptions) => string;
+  duration: (seconds: number) => string;
+}
+
+// makeFormat binds the pure helpers to one locale.
+export function makeFormat(locale: string): FormatApi {
+  return {
+    date: (value, options) => formatDateIn(locale, value, options),
+    time: (value, options) => formatTimeIn(locale, value, options),
+    dateTime: (value, options) => formatDateTimeIn(locale, value, options),
+    number: (value, options) => formatNumberIn(locale, value, options),
+    relative: (value, unit) => formatRelativeIn(locale, value, unit),
+    list: (items, options) => formatListIn(locale, items, options),
+    duration: (seconds) => formatDurationIn(locale, seconds),
+  };
+}
+
+// FALLBACK_INTL serves components rendered outside an IntlProvider (isolated
+// tests); it is English with no catalog.
+const FALLBACK_INTL: IntlShape = createIntl({ locale: "en", defaultLocale: "en", onError: onIntlError });
+
+// useOptionalIntl returns the provided IntlShape, or the English fallback when
+// no IntlProvider is mounted. Unlike useIntl() it never throws.
+export function useOptionalIntl(): IntlShape {
+  const provided: IntlShape | null = useContext(IntlContext);
+  return provided ?? FALLBACK_INTL;
+}
+
+export function useFormat(): FormatApi {
+  const intl = useOptionalIntl();
+  return useMemo(() => makeFormat(intl.locale), [intl.locale]);
+}
diff --git a/web/src/lib/i18n/languages.test.ts b/web/src/lib/i18n/languages.test.ts
new file mode 100644
index 000000000..ba053f7ad
--- /dev/null
+++ b/web/src/lib/i18n/languages.test.ts
@@ -0,0 +1,76 @@
+import { describe, expect, it, vi } from "vitest";
+import {
+  ENGLISH,
+  allLanguages,
+  directionFor,
+  isListed,
+  listedLanguages,
+  loadCatalogFrom,
+  parseManifests,
+  type LanguageInfo,
+} from "./languages";
+
+const fr: LanguageInfo = {
+  tag: "fr",
+  nativeName: "Français",
+  englishName: "French",
+  direction: "ltr",
+  completeness: 80,
+  listed: true,
+};
+
+describe("parseManifests", () => {
+  it("always includes English, prepended when the manifest omits it", () => {
+    expect(parseManifests({})).toEqual([ENGLISH]);
+    expect(parseManifests({ "/x.json": [fr] })).toEqual([ENGLISH, fr]);
+  });
+
+  it("keeps the manifest's English row when present", () => {
+    const manifestEn: LanguageInfo = { ...ENGLISH, completeness: 99 };
+    expect(parseManifests({ "/x.json": [manifestEn, fr] })).toEqual([manifestEn, fr]);
+  });
+
+  it("skips non-array modules and malformed rows", () => {
+    const bad = { tag: "xx" } as unknown as LanguageInfo;
+    expect(parseManifests({ "/x.json": undefined, "/y.json": [bad, fr] })).toEqual([ENGLISH, fr]);
+  });
+});
+
+describe("manifest accessors", () => {
+  it("contain English and report it as listed", () => {
+    expect(allLanguages().map((row) => row.tag)).toContain("en");
+    expect(isListed("en")).toBe(true);
+    expect(listedLanguages().some((row) => row.tag === "en")).toBe(true);
+  });
+
+  it("report unknown tags as unlisted and default their direction to ltr", () => {
+    expect(isListed("zz")).toBe(false);
+    expect(directionFor("zz")).toBe("ltr");
+    expect(directionFor("ar", [{ ...fr, tag: "ar", direction: "rtl" }])).toBe("rtl");
+  });
+});
+
+describe("loadCatalogFrom", () => {
+  it("returns the chunk for a tag with a generated catalog", async () => {
+    const chunk = { "server.generic.x": [] };
+    const loaders = { "/src/generated/i18n/fr.json": vi.fn(() => Promise.resolve(chunk)) };
+    await expect(loadCatalogFrom(loaders, "fr")).resolves.toBe(chunk);
+    expect(loaders["/src/generated/i18n/fr.json"]).toHaveBeenCalledOnce();
+  });
+
+  it("returns null when no chunk exists for the tag", async () => {
+    await expect(loadCatalogFrom({}, "de")).resolves.toBeNull();
+  });
+
+  it("returns null when the chunk is not an object", async () => {
+    const loaders = { "/src/generated/i18n/fr.json": () => Promise.resolve([1, 2]) };
+    await expect(loadCatalogFrom(loaders, "fr")).resolves.toBeNull();
+    const nullLoader = { "/src/generated/i18n/fr.json": () => Promise.resolve(null) };
+    await expect(loadCatalogFrom(nullLoader, "fr")).resolves.toBeNull();
+  });
+
+  it("does not load a file whose tag is not a plain catalog key", async () => {
+    const loaders = { "/src/generated/i18n/fr.json": () => Promise.resolve({}) };
+    await expect(loadCatalogFrom(loaders, "../languages")).resolves.toBeNull();
+  });
+});
diff --git a/web/src/lib/i18n/languages.ts b/web/src/lib/i18n/languages.ts
new file mode 100644
index 000000000..a024588a9
--- /dev/null
+++ b/web/src/lib/i18n/languages.ts
@@ -0,0 +1,124 @@
+import type { MessageFormatElement } from "react-intl";
+
+// LanguageInfo is one row of the language manifest computed by the shared Go
+// checker (`i18n-check --manifest`); the dashboard never derives listing rules
+// itself.
+export interface LanguageInfo {
+  tag: string;
+  nativeName: string;
+  englishName: string;
+  direction: "ltr" | "rtl";
+  completeness: number;
+  listed: boolean;
+}
+
+export const ENGLISH: LanguageInfo = {
+  tag: "en",
+  nativeName: "English",
+  englishName: "English",
+  direction: "ltr",
+  completeness: 100,
+  listed: true,
+};
+
+// CompiledCatalog maps each message id to its compiled AST (formatjs --ast).
+export type CompiledCatalog = Record<string, MessageFormatElement[]>;
+
+const manifests = import.meta.glob<LanguageInfo[]>("/src/generated/i18n/languages.json", {
+  eager: true,
+  import: "default",
+});
+
+// Fixture manifest for E2E builds only (npm run i18n:fixtures, or
+// VITE_I18N_FIXTURES=1). Release builds never write it, so no fixture language
+// is listed there.
+const fixtureManifests = import.meta.glob<LanguageInfo[]>("/src/generated/i18n/languages.fixtures.json", {
+  eager: true,
+  import: "default",
+});
+
+// Pseudo-language manifest (en-XA) for VITE_I18N_PSEUDO=1 builds only; see
+// scripts/i18n-pseudo.mjs. Absent in release builds.
+const pseudoManifests = import.meta.glob<LanguageInfo[]>("/src/generated/i18n/languages.pseudo.json", {
+  eager: true,
+  import: "default",
+});
+
+const catalogs = import.meta.glob<Record<string, unknown>>(
+  [
+    "/src/generated/i18n/*.json",
+    "!/src/generated/i18n/languages.json",
+    "!/src/generated/i18n/languages.fixtures.json",
+    "!/src/generated/i18n/languages.pseudo.json",
+    "!/src/generated/i18n/extracted.json",
+  ],
+  { import: "default" },
+);
+
+function isLanguageInfo(value: unknown): value is LanguageInfo {
+  if (typeof value !== "object" || value === null) return false;
+  const row = value as Partial<LanguageInfo>;
+  return (
+    typeof row.tag === "string" &&
+    typeof row.nativeName === "string" &&
+    typeof row.englishName === "string" &&
+    (row.direction === "ltr" || row.direction === "rtl") &&
+    typeof row.completeness === "number" &&
+    typeof row.listed === "boolean"
+  );
+}
+
+// parseManifests flattens the eagerly loaded manifest modules into one list
+// that always contains English. Pure so tests can pass fixtures.
+export function parseManifests(records: Record<string, LanguageInfo[] | undefined>): LanguageInfo[] {
+  const rows: LanguageInfo[] = [];
+  for (const value of Object.values(records)) {
+    if (!Array.isArray(value)) continue;
+    for (const row of value) {
+      if (isLanguageInfo(row)) rows.push(row);
+    }
+  }
+  if (rows.some((row) => row.tag === ENGLISH.tag)) return rows;
+  return [ENGLISH, ...rows];
+}
+
+let allCache: LanguageInfo[] | null = null;
+
+// allLanguages returns the manifest entries (or just English when the
+// generated manifest is absent, e.g. before `npm run build`).
+export function allLanguages(): LanguageInfo[] {
+  allCache ??= parseManifests({ ...manifests, ...fixtureManifests, ...pseudoManifests });
+  return allCache;
+}
+
+export function listedLanguages(): LanguageInfo[] {
+  return allLanguages().filter((row) => row.listed);
+}
+
+export function isListed(tag: string): boolean {
+  return listedLanguages().some((row) => row.tag === tag);
+}
+
+// directionFor returns the text direction for a tag; unknown tags are ltr.
+export function directionFor(tag: string, languages: readonly LanguageInfo[] = allLanguages()): "ltr" | "rtl" {
+  return languages.find((row) => row.tag === tag)?.direction ?? "ltr";
+}
+
+// CatalogLoaders maps a glob path to a lazy loader, as import.meta.glob returns.
+export type CatalogLoaders = Record<string, () => Promise<unknown>>;
+
+// loadCatalogFrom resolves one locale's compiled chunk from a loader map, or
+// null when no chunk was generated for the tag.
+export async function loadCatalogFrom(loaders: CatalogLoaders, tag: string): Promise<CompiledCatalog | null> {
+  const loader = loaders[`/src/generated/i18n/${tag}.json`];
+  if (!loader) return null;
+  const data = await loader();
+  if (typeof data !== "object" || data === null || Array.isArray(data)) return null;
+  // The chunk is produced by `formatjs compile --ast` at build time, so every
+  // value is a MessageFormatElement[]; the runtime cannot check that cheaply.
+  return data as CompiledCatalog;
+}
+
+export function loadMessages(tag: string): Promise<CompiledCatalog | null> {
+  return loadCatalogFrom(catalogs, tag);
+}
diff --git a/web/src/lib/i18n/pseudo.test.ts b/web/src/lib/i18n/pseudo.test.ts
new file mode 100644
index 000000000..1c5f7e7ed
--- /dev/null
+++ b/web/src/lib/i18n/pseudo.test.ts
@@ -0,0 +1,87 @@
+import { describe, expect, it } from "vitest";
+import { parse, TYPE } from "@formatjs/icu-messageformat-parser";
+import type { MessageFormatElement } from "@formatjs/icu-messageformat-parser";
+import {
+  accent,
+  buildPseudoCatalog,
+  pseudoLiteral,
+  pseudoLocalizeAst,
+  pseudoLocalizeMessage,
+  pseudoManifestEntry,
+} from "../../../scripts/i18n-pseudo-lib.mjs";
+
+// shape strips literal text so two ASTs can be compared by structure only.
+function shape(elements: MessageFormatElement[]): unknown {
+  return elements.map((el) => {
+    switch (el.type) {
+      case TYPE.literal:
+        return "lit";
+      case TYPE.tag:
+        return { tag: el.value, children: shape(el.children) };
+      case TYPE.plural:
+      case TYPE.select:
+        return {
+          type: el.type,
+          value: el.value,
+          options: Object.fromEntries(Object.entries(el.options).map(([k, o]) => [k, shape(o.value)])),
+        };
+      default:
+        return { type: el.type, value: (el as { value: string }).value };
+    }
+  });
+}
+
+describe("pseudo-locale transform", () => {
+  it("accents letters and leaves other characters alone", () => {
+    expect(accent("Save 1!")).toBe("Šáṽé 1!");
+  });
+
+  it("lengthens literals by about 40% and leaves whitespace alone", () => {
+    const out = pseudoLiteral("Start server");
+    expect([...out].length).toBe(12 + Math.ceil(12 * 0.4));
+    expect(pseudoLiteral("  ")).toBe("  ");
+  });
+
+  it("wraps the message in brackets", () => {
+    const ast = pseudoLocalizeMessage("Hello");
+    expect(ast[0]).toEqual({ type: TYPE.literal, value: "[" });
+    expect(ast[ast.length - 1]).toEqual({ type: TYPE.literal, value: "]" });
+  });
+
+  it("keeps placeholders, plural, select, pound and rich-text tags intact", () => {
+    const message =
+      "Hi {name}, you have {count, plural, one {# server} other {# servers}} <b>online</b> {kind, select, a {Alpha} other {Other}}";
+    const original = parse(message);
+    const pseudo = pseudoLocalizeMessage(message);
+    const inner = pseudo.slice(1, -1);
+    expect(shape(inner)).toEqual(shape(original));
+    const plural = inner.find((el) => el.type === TYPE.plural);
+    expect(plural?.type === TYPE.plural && plural.options.one?.value[0]?.type).toBe(TYPE.pound);
+  });
+
+  it("accents literals nested in tags and plural options", () => {
+    const ast = pseudoLocalizeMessage("<b>bold</b> {n, plural, other {items}}");
+    const text = JSON.stringify(ast);
+    expect(text).toContain("ƀóļð");
+    expect(text).toContain("íţéɱš");
+    expect(text).not.toContain('"bold"');
+  });
+
+  it("is idempotent in structure when applied to an AST directly", () => {
+    const ast = pseudoLocalizeAst(parse("Plain text"));
+    expect(ast).toHaveLength(3);
+  });
+
+  it("builds a catalog keyed by id, sorted", () => {
+    const catalog = buildPseudoCatalog({
+      "b.id": { defaultMessage: "Two" },
+      "a.id": { defaultMessage: "One {x}" },
+    });
+    expect(Object.keys(catalog)).toEqual(["a.id", "b.id"]);
+    expect(catalog["a.id"]?.some((el) => el.type === TYPE.argument)).toBe(true);
+  });
+
+  it("declares a listed left-to-right manifest row for en-XA", () => {
+    expect(pseudoManifestEntry).toMatchObject({ tag: "en-XA", nativeName: "Pseudo", direction: "ltr", listed: true });
+  });
+});
diff --git a/web/src/lib/i18n/resolve.test.ts b/web/src/lib/i18n/resolve.test.ts
new file mode 100644
index 000000000..dc6d5b884
--- /dev/null
+++ b/web/src/lib/i18n/resolve.test.ts
@@ -0,0 +1,70 @@
+import { describe, expect, it } from "vitest";
+import { matchListed, resolveLanguage } from "./resolve";
+
+const listed = ["en", "fr", "de", "pt-BR"];
+
+describe("matchListed", () => {
+  it("matches exactly, case-insensitively, and returns the listed spelling", () => {
+    expect(matchListed("FR", listed)).toBe("fr");
+    expect(matchListed("pt-br", listed)).toBe("pt-BR");
+  });
+
+  it("falls back from a regional tag to its base language", () => {
+    expect(matchListed("fr-CA", listed)).toBe("fr");
+    expect(matchListed("de-AT", listed)).toBe("de");
+  });
+
+  it("returns null for unlisted, empty, or blank tags", () => {
+    expect(matchListed("ja", listed)).toBeNull();
+    expect(matchListed("ja-JP", listed)).toBeNull();
+    expect(matchListed("", listed)).toBeNull();
+    expect(matchListed("   ", listed)).toBeNull();
+  });
+});
+
+describe("resolveLanguage", () => {
+  it("prefers the user choice over every other step", () => {
+    expect(
+      resolveLanguage({
+        userChoice: "de",
+        browserChoice: "fr",
+        navigatorLanguages: ["fr"],
+        instanceDefault: "fr",
+        listed,
+      }),
+    ).toBe("de");
+  });
+
+  it("uses the browser choice when there is no user choice", () => {
+    expect(
+      resolveLanguage({ browserChoice: "fr", navigatorLanguages: ["de"], instanceDefault: "de", listed }),
+    ).toBe("fr");
+  });
+
+  it("walks navigator languages in order, with regional before base", () => {
+    expect(resolveLanguage({ navigatorLanguages: ["ja", "fr-CA", "de"], listed })).toBe("fr");
+    expect(resolveLanguage({ navigatorLanguages: ["pt-BR"], listed })).toBe("pt-BR");
+  });
+
+  it("uses the instance default when no earlier step matches", () => {
+    expect(resolveLanguage({ navigatorLanguages: ["ja"], instanceDefault: "de", listed })).toBe("de");
+  });
+
+  it("skips unlisted candidates at every step", () => {
+    expect(
+      resolveLanguage({
+        userChoice: "ja",
+        browserChoice: "ko",
+        navigatorLanguages: ["zh-CN"],
+        instanceDefault: "it",
+        listed,
+      }),
+    ).toBe("en");
+  });
+
+  it("falls back to en when nothing is provided", () => {
+    expect(resolveLanguage({ listed: [] })).toBe("en");
+    expect(resolveLanguage({ userChoice: null, browserChoice: null, instanceDefault: null, listed })).toBe("en");
+    expect(resolveLanguage({ userChoice: "", listed })).toBe("en");
+  });
+});
diff --git a/web/src/lib/i18n/resolve.ts b/web/src/lib/i18n/resolve.ts
new file mode 100644
index 000000000..67e3776a2
--- /dev/null
+++ b/web/src/lib/i18n/resolve.ts
@@ -0,0 +1,41 @@
+// Language resolution (spec 019, FR-004). The first candidate that matches a
+// listed language wins; English is the terminal fallback.
+
+export interface ResolveInput {
+  userChoice?: string | null;
+  browserChoice?: string | null;
+  navigatorLanguages?: readonly string[];
+  instanceDefault?: string | null;
+  listed: readonly string[];
+}
+
+// matchListed maps a BCP 47 tag onto a listed language: an exact
+// (case-insensitive) match first, then the base language before "-"
+// (so `fr-CA` resolves to `fr`). Returns the listed spelling or null.
+export function matchListed(tag: string, listed: readonly string[]): string | null {
+  const wanted = tag.trim().toLowerCase();
+  if (wanted === "") return null;
+  const exact = listed.find((candidate) => candidate.toLowerCase() === wanted);
+  if (exact !== undefined) return exact;
+  const base = wanted.split("-")[0];
+  if (base === undefined || base === wanted) return null;
+  return listed.find((candidate) => candidate.toLowerCase() === base) ?? null;
+}
+
+// resolveLanguage applies the order: user choice, browser choice, each
+// navigator language (regional, then base), instance default, then "en".
+// Candidates that do not match a listed language are skipped.
+export function resolveLanguage(input: ResolveInput): string {
+  const candidates: (string | null | undefined)[] = [
+    input.userChoice,
+    input.browserChoice,
+    ...(input.navigatorLanguages ?? []),
+    input.instanceDefault,
+  ];
+  for (const candidate of candidates) {
+    if (!candidate) continue;
+    const matched = matchListed(candidate, input.listed);
+    if (matched !== null) return matched;
+  }
+  return "en";
+}
diff --git a/web/src/lib/i18n/serverMessage.test.tsx b/web/src/lib/i18n/serverMessage.test.tsx
new file mode 100644
index 000000000..13ac40389
--- /dev/null
+++ b/web/src/lib/i18n/serverMessage.test.tsx
@@ -0,0 +1,107 @@
+import { render, screen } from "@testing-library/react";
+import { describe, expect, it } from "vitest";
+import { createIntl, IntlProvider } from "react-intl";
+import type { IntlShape } from "react-intl";
+
+import { APIError } from "@/lib/api";
+import { errorText, errorTextIntl } from "@/lib/errors";
+import { serverMessageText, useServerMessage } from "./serverMessage";
+
+const PROBLEM = "application/problem+json";
+
+function problem(body: Record<string, unknown>): APIError {
+  return new APIError(409, JSON.stringify(body), "Conflict", PROBLEM);
+}
+
+function intlWith(messages: Record<string, string>): IntlShape {
+  return createIntl({ locale: "fr", defaultLocale: "en", messages, onError: () => {} });
+}
+
+describe("serverMessageText", () => {
+  it("returns null for errors that are not APIError", () => {
+    expect(serverMessageText(intlWith({}), new Error("nope"))).toBeNull();
+    expect(serverMessageText(intlWith({}), "string")).toBeNull();
+  });
+
+  it("returns null when the APIError has no messageId", () => {
+    const err = new APIError(500, "plain body", "Server Error", "text/plain");
+    expect(serverMessageText(intlWith({ "server.x": "Texte" }), err)).toBeNull();
+  });
+
+  it("returns null when the messageId is not in the catalog", () => {
+    const err = problem({ detail: "English", messageId: "server.unknown" });
+    expect(serverMessageText(intlWith({}), err)).toBeNull();
+  });
+
+  it("formats the translated message with the problem args", () => {
+    const err = problem({
+      detail: "server is at 5 of 3",
+      messageId: "server.limit.reached",
+      args: { max: 3 },
+    });
+    const intl = intlWith({ "server.limit.reached": "Limite de {max} atteinte" });
+    expect(serverMessageText(intl, err)).toBe("Limite de 3 atteinte");
+  });
+
+  it("appends the English detail for server.generic.* ids when it differs", () => {
+    const err = problem({
+      detail: "pod evicted",
+      messageId: "server.generic.failed",
+    });
+    const intl = intlWith({ "server.generic.failed": "Échec de l'opération" });
+    expect(serverMessageText(intl, err)).toBe("Échec de l'opération pod evicted");
+  });
+
+  it("does not repeat the detail when it equals the translated text", () => {
+    const err = problem({ detail: "Échec", messageId: "server.generic.same" });
+    const intl = intlWith({ "server.generic.same": "Échec" });
+    expect(serverMessageText(intl, err)).toBe("Échec");
+  });
+
+  it("does not append detail for non-generic ids", () => {
+    const err = problem({ detail: "extra", messageId: "server.named" });
+    const intl = intlWith({ "server.named": "Nommé" });
+    expect(serverMessageText(intl, err)).toBe("Nommé");
+  });
+
+  it("does not append an empty detail", () => {
+    const err = problem({ detail: "", messageId: "server.generic.empty" });
+    const intl = intlWith({ "server.generic.empty": "Vide" });
+    expect(serverMessageText(intl, err)).toBe("Vide");
+  });
+});
+
+describe("errorTextIntl", () => {
+  it("prefers the translated server message", () => {
+    const err = problem({ detail: "English", messageId: "server.named" });
+    expect(errorTextIntl(intlWith({ "server.named": "Nommé" }), err, "fallback")).toBe("Nommé");
+  });
+
+  it("falls back to errorText when the message is not translated", () => {
+    const err = new APIError(400, JSON.stringify({ error: "bad input" }), "Bad Request", "application/json");
+    expect(errorTextIntl(intlWith({}), err, "fallback")).toBe(errorText(err, "fallback"));
+    expect(errorTextIntl(intlWith({}), new Error("boom"), "fallback")).toBe("boom");
+  });
+});
+
+describe("useServerMessage", () => {
+  function Message({ err }: { err: unknown }) {
+    return <p>{useServerMessage(err) ?? "none"}</p>;
+  }
+
+  it("translates through the surrounding IntlProvider", () => {
+    const err = problem({ detail: "English", messageId: "server.named" });
+    render(
+      <IntlProvider locale="fr" defaultLocale="en" messages={{ "server.named": "Nommé" }}>
+        <Message err={err} />
+      </IntlProvider>,
+    );
+    expect(screen.getByText("Nommé")).toBeInTheDocument();
+  });
+
+  it("returns null outside a provider so callers keep their English text", () => {
+    const err = problem({ detail: "English", messageId: "server.named" });
+    render(<Message err={err} />);
+    expect(screen.getByText("none")).toBeInTheDocument();
+  });
+});
diff --git a/web/src/lib/i18n/serverMessage.ts b/web/src/lib/i18n/serverMessage.ts
new file mode 100644
index 000000000..e4da5a648
--- /dev/null
+++ b/web/src/lib/i18n/serverMessage.ts
@@ -0,0 +1,33 @@
+import type { IntlShape } from "react-intl";
+
+import { APIError } from "@/lib/api";
+
+import { useOptionalIntl } from "./format";
+
+// serverMessageText returns the translated text for an API error carrying a
+// messageId (problem+json) that exists in the active catalog. Returns null when
+// the error has no messageId or the id is not translated, so the caller keeps
+// its existing English text.
+export function serverMessageText(intl: IntlShape, err: unknown): string | null {
+  if (!(err instanceof APIError) || !err.messageId) return null;
+  const id = err.messageId;
+  if (!Object.hasOwn(intl.messages, id)) return null;
+  // The id comes from the API response; its English text and translator note
+  // live in the server.* catalog entries (api/internal/messages), not here.
+  const formatted: unknown = intl.formatMessage(
+    { id, description: "API error; text and note come from the server.* catalog entry" },
+    err.args,
+  );
+  if (typeof formatted !== "string") return null;
+  // Generic server errors carry a free-form English detail (for example the
+  // underlying Kubernetes message) that is shown after the translated sentence.
+  if (id.startsWith("server.generic.") && err.detail && err.detail !== formatted) {
+    return `${formatted} ${err.detail}`;
+  }
+  return formatted;
+}
+
+// useServerMessage is serverMessageText bound to the active intl instance.
+export function useServerMessage(err: unknown): string | null {
+  return serverMessageText(useOptionalIntl(), err);
+}
diff --git a/web/src/lib/i18n/storage.test.ts b/web/src/lib/i18n/storage.test.ts
new file mode 100644
index 000000000..9c2e6e170
--- /dev/null
+++ b/web/src/lib/i18n/storage.test.ts
@@ -0,0 +1,62 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { LANGUAGE_STORAGE_KEY, readLanguageStorage, writeLanguageStorage } from "./storage";
+
+describe("language storage", () => {
+  beforeEach(() => {
+    window.localStorage.clear();
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    window.localStorage.clear();
+  });
+
+  it("reads nulls when nothing is stored", () => {
+    expect(readLanguageStorage()).toEqual({ choice: null, applied: null });
+  });
+
+  it("reads choice and applied when stored", () => {
+    window.localStorage.setItem(LANGUAGE_STORAGE_KEY, JSON.stringify({ choice: "fr", applied: "fr" }));
+    expect(readLanguageStorage()).toEqual({ choice: "fr", applied: "fr" });
+  });
+
+  it("treats bad JSON, non-objects, and wrong field types as empty", () => {
+    window.localStorage.setItem(LANGUAGE_STORAGE_KEY, "{not json");
+    expect(readLanguageStorage()).toEqual({ choice: null, applied: null });
+
+    window.localStorage.setItem(LANGUAGE_STORAGE_KEY, "42");
+    expect(readLanguageStorage()).toEqual({ choice: null, applied: null });
+
+    window.localStorage.setItem(LANGUAGE_STORAGE_KEY, "null");
+    expect(readLanguageStorage()).toEqual({ choice: null, applied: null });
+
+    window.localStorage.setItem(LANGUAGE_STORAGE_KEY, JSON.stringify({ choice: 7, applied: ["fr"] }));
+    expect(readLanguageStorage()).toEqual({ choice: null, applied: null });
+  });
+
+  it("merges a patch into the stored value", () => {
+    writeLanguageStorage({ choice: "fr" });
+    writeLanguageStorage({ applied: "fr" });
+    expect(readLanguageStorage()).toEqual({ choice: "fr", applied: "fr" });
+  });
+
+  it("clears the choice when the patch sets it to null", () => {
+    writeLanguageStorage({ choice: "de", applied: "de" });
+    writeLanguageStorage({ choice: null });
+    expect(readLanguageStorage()).toEqual({ choice: null, applied: "de" });
+  });
+
+  it("ignores read failures from a throwing localStorage", () => {
+    vi.spyOn(Storage.prototype, "getItem").mockImplementation(() => {
+      throw new Error("blocked");
+    });
+    expect(readLanguageStorage()).toEqual({ choice: null, applied: null });
+  });
+
+  it("ignores write failures from a throwing localStorage", () => {
+    vi.spyOn(Storage.prototype, "setItem").mockImplementation(() => {
+      throw new Error("quota");
+    });
+    expect(() => writeLanguageStorage({ choice: "fr" })).not.toThrow();
+  });
+});
diff --git a/web/src/lib/i18n/storage.ts b/web/src/lib/i18n/storage.ts
new file mode 100644
index 000000000..c378dd34b
--- /dev/null
+++ b/web/src/lib/i18n/storage.ts
@@ -0,0 +1,43 @@
+// Per-browser language preference (spec 019, FR-005). The value is
+// `{choice, applied}`: `choice` is what the viewer picked on this browser,
+// `applied` is the language last rendered (read pre-React by the boot snippet
+// in index.html). Storage can be unavailable (private mode, blocked site data),
+// so every access is guarded and failures degrade to "no preference".
+
+export const LANGUAGE_STORAGE_KEY = "gameplane-language";
+
+export interface LanguageStorage {
+  choice: string | null;
+  applied: string | null;
+}
+
+const EMPTY: LanguageStorage = { choice: null, applied: null };
+
+export function readLanguageStorage(): LanguageStorage {
+  try {
+    const raw = window.localStorage.getItem(LANGUAGE_STORAGE_KEY);
+    if (!raw) return { ...EMPTY };
+    const parsed: unknown = JSON.parse(raw);
+    if (typeof parsed !== "object" || parsed === null) return { ...EMPTY };
+    const record = parsed as Partial<Record<keyof LanguageStorage, unknown>>;
+    return {
+      choice: typeof record.choice === "string" ? record.choice : null,
+      applied: typeof record.applied === "string" ? record.applied : null,
+    };
+  } catch {
+    return { ...EMPTY };
+  }
+}
+
+export function writeLanguageStorage(patch: { choice?: string | null; applied?: string }): void {
+  try {
+    const current = readLanguageStorage();
+    const next: LanguageStorage = {
+      choice: patch.choice !== undefined ? patch.choice : current.choice,
+      applied: patch.applied !== undefined ? patch.applied : current.applied,
+    };
+    window.localStorage.setItem(LANGUAGE_STORAGE_KEY, JSON.stringify(next));
+  } catch {
+    // Storage unavailable: the language still applies for this page view.
+  }
+}
diff --git a/web/src/main.tsx b/web/src/main.tsx
index 989f1a7ec..687cd73ec 100644
--- a/web/src/main.tsx
+++ b/web/src/main.tsx
@@ -6,6 +6,7 @@ import { RouterProvider as AriaRouterProvider } from "react-aria-components";
 
 import { routeTree } from "@/router/tree";
 import { createAriaNavigate, createAriaUseHref } from "@/lib/ariaRouter";
+import { AppI18nProvider } from "@/lib/i18n/I18nProvider";
 import "@/styles/globals.css";
 
 const router = createRouter({ routeTree });
@@ -34,12 +35,14 @@ async function bootstrap(): Promise<void> {
   ReactDOM.createRoot(document.getElementById("root")!).render(
     <React.StrictMode>
       <QueryClientProvider client={queryClient}>
-        <AriaRouterProvider
-          navigate={createAriaNavigate(router)}
-          useHref={createAriaUseHref(router)}
-        >
-          <RouterProvider router={router} />
-        </AriaRouterProvider>
+        <AppI18nProvider>
+          <AriaRouterProvider
+            navigate={createAriaNavigate(router)}
+            useHref={createAriaUseHref(router)}
+          >
+            <RouterProvider router={router} />
+          </AriaRouterProvider>
+        </AppI18nProvider>
       </QueryClientProvider>
     </React.StrictMode>,
   );
diff --git a/web/src/routes/AdminSettings.tsx b/web/src/routes/AdminSettings.tsx
index 75f8f8445..cc6b3ee22 100644
--- a/web/src/routes/AdminSettings.tsx
+++ b/web/src/routes/AdminSettings.tsx
@@ -74,6 +74,7 @@ import {
 } from "@/lib/config";
 import { ErrorBanner } from "@/components/backups/ErrorBanner";
 import { ModuleSourcesPanel } from "@/components/modules/ModuleSourcesPanel";
+import { useFormat, type FormatApi } from "@/lib/i18n/format";
 
 type Section =
   | "general" | "auth" | "backups" | "modules" | "modRegistries" | "notifications"
@@ -1624,16 +1625,16 @@ const TELEMETRY_KEY = ["telemetry"] as const;
 
 // Intl output is "Oct 6, 2026, 09:12" for these options; the section always
 // renders UTC so the text matches what the receiver stores.
-function formatUtc(iso: string, withTime: boolean): string {
+function formatUtc(iso: string, withTime: boolean, fmt: FormatApi): string {
   const d = new Date(iso);
   if (Number.isNaN(d.getTime())) return iso;
-  const text = new Intl.DateTimeFormat("en-US", {
+  const text = fmt.dateTime(d, {
     month: "short",
     day: "numeric",
     year: "numeric",
     ...(withTime ? { hour: "2-digit", minute: "2-digit", hourCycle: "h23" as const } : {}),
     timeZone: "UTC",
-  }).format(d);
+  });
   return withTime ? `${text} UTC` : text;
 }
 
@@ -1736,12 +1737,13 @@ function TelemetryPreviewBlock({ info }: { info: TelemetryInfo }) {
 
 function TelemetryStatusLines({ info }: { info: TelemetryInfo }) {
   const { status } = info;
+  const fmt = useFormat();
   let text: string;
   if (status.lastOutcome === "ok") {
-    text = `Last report sent successfully on ${status.lastSuccessAt ? formatUtc(status.lastSuccessAt, true) : "an earlier attempt"}.`;
+    text = `Last report sent successfully on ${status.lastSuccessAt ? formatUtc(status.lastSuccessAt, true, fmt) : "an earlier attempt"}.`;
   } else if (status.lastOutcome === "failed") {
     text = status.lastSuccessAt
-      ? `Last attempt failed, will retry. Last successful report: ${formatUtc(status.lastSuccessAt, true)}.`
+      ? `Last attempt failed, will retry. Last successful report: ${formatUtc(status.lastSuccessAt, true, fmt)}.`
       : "Last attempt failed, will retry. No report has been delivered yet.";
   } else {
     text = "No report sent yet.";
@@ -1751,7 +1753,7 @@ function TelemetryStatusLines({ info }: { info: TelemetryInfo }) {
       <div>{text}</div>
       {status.lastIdRotationAt && (
         <div>
-          Install ID replaced on {formatUtc(status.lastIdRotationAt, false)}: the destination
+          Install ID replaced on {formatUtc(status.lastIdRotationAt, false, fmt)}: the destination
           reported it was in use by another key.
         </div>
       )}
diff --git a/web/src/routes/ThemeSettings.tsx b/web/src/routes/ThemeSettings.tsx
index 531b6d77c..25afedf22 100644
--- a/web/src/routes/ThemeSettings.tsx
+++ b/web/src/routes/ThemeSettings.tsx
@@ -44,6 +44,7 @@ import {
 import { MAX_CUSTOM_CSS_LEN, sanitizeCustomCss, type SanitizeResult } from "@/lib/theme-sanitize";
 import { buildThemeExport, validateThemeExport } from "@/lib/theme-export";
 import type { AppearanceMode, CustomColorConfig, ThemePresetId, UserThemePreferences } from "@/types";
+import { useFormat, type FormatApi } from "@/lib/i18n/format";
 
 // Dark-mode accent/surface pair per preset, per contracts/theme-ui.md §3.1
 // and the lWvcv swatch fills.
@@ -106,7 +107,7 @@ function findLine(css: string, re: RegExp): { line: number; text: string } | nul
   return null;
 }
 
-function editorErrorMessage(css: string, result: Extract<SanitizeResult, { ok: false }>): string {
+function editorErrorMessage(css: string, result: Extract<SanitizeResult, { ok: false }>, fmt: FormatApi): string {
   const err = result.error;
   if (err.includes("@import")) {
     const hit = findLine(css, /@import/i);
@@ -124,7 +125,7 @@ function editorErrorMessage(css: string, result: Extract<SanitizeResult, { ok: f
     return "Syntax error: unbalanced braces — every '{' must have a matching '}'.";
   }
   if (err.includes("maximum length")) {
-    return `Custom CSS exceeds the ${MAX_CUSTOM_CSS_LEN.toLocaleString("en-US")}-byte limit.`;
+    return `Custom CSS exceeds the ${fmt.number(MAX_CUSTOM_CSS_LEN)}-byte limit.`;
   }
   if (err.includes("HTML delimiter")) {
     return "HTML <style> and <script> tags are not allowed in custom CSS.";
@@ -147,6 +148,7 @@ function ThemeCard({ title, subtitle, children }: { title: string; subtitle: str
 }
 
 export function ThemeSettingsPage() {
+  const fmt = useFormat();
   const { data: me } = useMe();
   const navigate = useNavigate();
   const queryClient = useQueryClient();
@@ -281,7 +283,7 @@ export function ThemeSettingsPage() {
   const cssDraft = draft?.customCss ?? "";
   const cssBytes = utf8Len(cssDraft);
   const cssResult = useMemo(() => sanitizeCustomCss(cssDraft), [cssDraft]);
-  const cssError = cssResult.ok ? null : editorErrorMessage(cssDraft, cssResult);
+  const cssError = cssResult.ok ? null : editorErrorMessage(cssDraft, cssResult, fmt);
 
   // Live preview: the draft applies to the DOM as it changes; applyThemePreferences
   // mounts the custom-color vars and re-appends #gameplane-custom-css last in <head>.
@@ -702,7 +704,7 @@ export function ThemeSettingsPage() {
                   />
                   <div className="flex items-center justify-between">
                     <span className="text-xs text-muted">
-                      {cssBytes.toLocaleString("en-US")} / {MAX_CUSTOM_CSS_LEN.toLocaleString("en-US")}
+                      {fmt.number(cssBytes)} / {fmt.number(MAX_CUSTOM_CSS_LEN)}
                     </span>
                   </div>
                 </div>
@@ -812,7 +814,7 @@ export function ThemeSettingsPage() {
                     <div className="text-xs text-muted">
                       Custom CSS:{" "}
                       {importPreview.preferences.customCss
-                        ? `${utf8Len(importPreview.preferences.customCss).toLocaleString("en-US")} bytes`
+                        ? `${fmt.number(utf8Len(importPreview.preferences.customCss))} bytes`
                         : "none"}
                     </div>
                     <div className="flex justify-end">
diff --git a/web/src/routes/tabs/Logs.tsx b/web/src/routes/tabs/Logs.tsx
index e69f62052..9c09022b2 100644
--- a/web/src/routes/tabs/Logs.tsx
+++ b/web/src/routes/tabs/Logs.tsx
@@ -6,6 +6,7 @@ import { Button, Input, Tabs, Tab as TabComponent } from "@heroui/react";
 
 
 
+import { useFormat } from "@/lib/i18n/format";
 import { openWS } from "@/lib/ws";
 import { capitalize, cn } from "@/lib/utils";
 import type { GameServerPhase } from "@/types";
@@ -58,6 +59,7 @@ export function LogsTab({
   const resourceTarget = useResourceTarget({ name, namespace: ns });
   const resourceClient = useResourceClient(resourceTarget);
   const { Logs } = resourceClient;
+  const fmt = useFormat();
 
   const [lines, setLines] = useState<string[]>([]);
   const [filter, setFilter] = useState("");
@@ -185,7 +187,7 @@ export function LogsTab({
             ))}
           </Tabs.List>
         </Tabs>
-        <span className="text-xs text-muted">{filtered.length.toLocaleString()} lines</span>
+        <span className="text-xs text-muted">{fmt.number(filtered.length)} lines</span>
         <div className="ml-auto">
           <Button
             size="sm"
diff --git a/web/src/routes/tabs/settings/NetworkCapture.tsx b/web/src/routes/tabs/settings/NetworkCapture.tsx
index 8c9982c60..47558819c 100644
--- a/web/src/routes/tabs/settings/NetworkCapture.tsx
+++ b/web/src/routes/tabs/settings/NetworkCapture.tsx
@@ -1,4 +1,5 @@
 import { useResourceAccess, useResourcePermissions, resourceCan } from "@/lib/resourceTarget";
+import { useFormat } from "@/lib/i18n/format";
 import { useEffect, useState } from "react";
 import {
   Input,
@@ -48,6 +49,7 @@ function bestUnit(seconds: number): RetentionUnit {
 }
 
 export function NetworkCaptureSection({ draft, onChange, onValidityChange }: SectionProps) {
+  const fmt = useFormat();
   const access = useResourceAccess();
   const permissionsReady = access?.permissions !== undefined;
   const permissions = useResourcePermissions();
@@ -91,7 +93,7 @@ export function NetworkCaptureSection({ draft, onChange, onValidityChange }: Sec
     const seconds = Math.round(n * UNIT_SECONDS[u]);
     if (seconds > CLUSTER_MAX_RETENTION_SECONDS) {
       setRetentionError(
-        `Exceeds the cluster maximum of 7 days (${CLUSTER_MAX_RETENTION_SECONDS.toLocaleString()} seconds).`,
+        `Exceeds the cluster maximum of 7 days (${fmt.number(CLUSTER_MAX_RETENTION_SECONDS)} seconds).`,
       );
       return;
     }
@@ -213,7 +215,7 @@ export function NetworkCaptureSection({ draft, onChange, onValidityChange }: Sec
             <FieldError className="text-xs">{retentionError}</FieldError>
           ) : (
             <p className="text-xs text-default-500">
-              Cluster maximum: 7 days ({CLUSTER_MAX_RETENTION_SECONDS.toLocaleString()} seconds)
+              Cluster maximum: 7 days ({fmt.number(CLUSTER_MAX_RETENTION_SECONDS)} seconds)
               — a storage-limitation-informed default, not a legal requirement.
             </p>
           )}
diff --git a/web/src/routes/tabs/settings/ShareLinks.tsx b/web/src/routes/tabs/settings/ShareLinks.tsx
index 1ffb940e4..e07aa47b4 100644
--- a/web/src/routes/tabs/settings/ShareLinks.tsx
+++ b/web/src/routes/tabs/settings/ShareLinks.tsx
@@ -34,6 +34,7 @@ import { AlertCircle, Calendar as CalendarIcon, Copy, Link2 } from "lucide-react
 import type { ShareLink } from "@/types";
 import { type ShareLinkCreateBody } from "@/lib/api";
 import { errorText } from "@/lib/errors";
+import { useFormat, type FormatApi } from "@/lib/i18n/format";
 
 interface ShareLinksProps {
   name: string;
@@ -141,10 +142,10 @@ function getLinkStatus(expiresAt: string | null, revokedAt?: string | null): str
 
 // Format date for display (e.g., "Jul 28, 2026"), or "Never" for a
 // no-expiry link (SC-004).
-function formatDate(dateStr: string | null): string {
+function formatDate(dateStr: string | null, fmt: FormatApi): string {
   if (dateStr === null) return "Never";
   const date = new Date(dateStr);
-  return date.toLocaleDateString("en-US", {
+  return fmt.date(date, {
     month: "short",
     day: "numeric",
     year: "numeric",
@@ -508,6 +509,7 @@ function RevokeDialog({
 
 // Main component
 export function ShareLinksSection({ name, ns }: ShareLinksProps) {
+  const fmt = useFormat();
   const resourceTarget = useResourceTarget({ name, namespace: ns });
   const resourceClient = useResourceClient(resourceTarget);
   const access = useResourceAccess();
@@ -584,8 +586,8 @@ export function ShareLinksSection({ name, ns }: ShareLinksProps) {
               <Table.Body>
                 {links?.map((link) => (
                   <Table.Row key={link.id}>
-                    <Table.Cell>{formatDate(link.createdAt)}</Table.Cell>
-                    <Table.Cell>{formatDate(link.expiresAt)}</Table.Cell>
+                    <Table.Cell>{formatDate(link.createdAt, fmt)}</Table.Cell>
+                    <Table.Cell>{formatDate(link.expiresAt, fmt)}</Table.Cell>
                     <Table.Cell>
                       <Chip
                         variant="soft"
diff --git a/web/src/test/handlers.ts b/web/src/test/handlers.ts
index dd6249304..9df85122a 100644
--- a/web/src/test/handlers.ts
+++ b/web/src/test/handlers.ts
@@ -104,6 +104,9 @@ export const handlers = [
       ],
     }),
   ),
+  // Pre-auth instance default language (spec 019). The dashboard asks for it
+  // on every page load; mock mode reports English.
+  http.get("/auth/locale", () => HttpResponse.json({ defaultLanguage: "en" })),
 
   // Cluster
   // Server-sent events stream the layout opens. Browser mock mode has a
@@ -835,6 +838,8 @@ export function buildScreenshotHandlers() {
     ...fleetHandlers,
     // The Servers page asks which namespaces to list before listing servers.
     http.get("/namespaces", () => HttpResponse.json({ namespaces: ["gameplane-games"] })),
+    // Pre-auth instance default language (spec 019).
+    http.get("/auth/locale", () => HttpResponse.json({ defaultLanguage: "en" })),
     // Auth: reuse default login/logout (screenshot demos don't test auth edge cases)
     http.get("/users/me", ({ cookies }) => {
       if (cookies.e2e_force_401 === "1") {
diff --git a/web/src/types.ts b/web/src/types.ts
index 04b034a09..880c2b72c 100644
--- a/web/src/types.ts
+++ b/web/src/types.ts
@@ -332,7 +332,15 @@ export interface GameTemplate {
       maxLength?: number;
     }>;
   };
-  status?: { inUseCount?: number };
+  status?: {
+    inUseCount?: number;
+    conditions?: Array<{
+      type: string;
+      status: string;
+      reason?: string;
+      message?: string;
+    }>;
+  };
 }
 
 export type GameServerPhase =
@@ -612,6 +620,11 @@ export interface GameServer {
       message?: string;
       lastTransitionTime?: string;
     }>;
+    // Per condition type, the values interpolated into that condition's
+    // English message. Pair it with the condition's reason to render the
+    // localized message (id condition.<type>.<reason>, lower-cased); the
+    // condition's message stays the fallback.
+    conditionArgs?: Record<string, Record<string, string>>;
     startedAt?: string;
     // Observed state of the capture sidecar for this server.
     capture?: CaptureStatus;
@@ -752,6 +765,9 @@ export interface UserThemePreferences {
   customCssEnabled: boolean;
   customCss?: string | null;
   updatedAt?: string;
+  // Saved dashboard language (BCP 47 tag). null or absent means no saved
+  // choice: the app falls back to the browser, then the instance default.
+  language?: string | null;
 }
 
 // Portable export document (FR-014, data-model.md §2.4; full schema in
diff --git a/web/vite.config.ts b/web/vite.config.ts
index f34dc51e0..20d7cab19 100644
--- a/web/vite.config.ts
+++ b/web/vite.config.ts
@@ -1,11 +1,43 @@
 import { defineConfig } from "vite";
+import type { Plugin } from "vite";
 import react from "@vitejs/plugin-react";
+import { execFileSync } from "node:child_process";
 import path from "node:path";
 import { fileURLToPath } from "node:url";
 
 // __dirname isn't defined in ESM; derive it from import.meta.url.
 const here = path.dirname(fileURLToPath(import.meta.url));
 
+// i18nFixtures: VITE_I18N_FIXTURES=1 writes the fixture language "zz" (spec 019,
+// T046) so the E2E i18n specs have a language with 0% completeness to switch to.
+// Fixtures are written only on request; release builds never request them, and
+// web/src/generated/ is gitignored, so a clean checkout never contains them.
+function i18nFixtures(): Plugin {
+  return {
+    name: "gameplane-i18n-fixtures",
+    configResolved() {
+      if (process.env.VITE_I18N_FIXTURES === "1") {
+        execFileSync(process.execPath, [path.resolve(here, "scripts/i18n-fixtures.mjs")], { stdio: "inherit" });
+      }
+    },
+  };
+}
+
+// i18nPseudo: VITE_I18N_PSEUDO=1 writes the pseudo-language "en-XA" (spec 019,
+// T099, FR-038) for the dev server (and the planned Playwright en-XA project,
+// T100). Release builds never set the flag, so en-XA never reaches a release
+// languages.json.
+function i18nPseudo(): Plugin {
+  return {
+    name: "gameplane-i18n-pseudo",
+    configResolved() {
+      if (process.env.VITE_I18N_PSEUDO === "1") {
+        execFileSync(process.execPath, [path.resolve(here, "scripts/i18n-pseudo.mjs")], { stdio: "inherit" });
+      }
+    },
+  };
+}
+
 // API target for the dev server's proxy. Defaults to the standard local
 // process; Playwright live-mode points it at a kubectl port-forward by
 // setting GAMEPLANE_API_URL=http://localhost:18080 before spawning vite.
@@ -23,9 +55,12 @@ function htmlBypass(req: { headers: Record<string, string | string[] | undefined
 }
 
 export default defineConfig({
-  plugins: [react()],
+  plugins: [react(), i18nFixtures(), i18nPseudo()],
   resolve: {
-    alias: { "@": path.resolve(here, "./src") },
+    alias: {
+      "@": path.resolve(here, "./src"),
+      "@i18n": path.resolve(here, "../i18n/locales"),
+    },
   },
   server: {
     port: 5173,
diff --git a/web/vitest.config.ts b/web/vitest.config.ts
index 946b089b7..4fd8ab870 100644
--- a/web/vitest.config.ts
+++ b/web/vitest.config.ts
@@ -8,7 +8,10 @@ const here = path.dirname(fileURLToPath(import.meta.url));
 export default defineConfig({
   plugins: [react()],
   resolve: {
-    alias: { "@": path.resolve(here, "./src") },
+    alias: {
+      "@": path.resolve(here, "./src"),
+      "@i18n": path.resolve(here, "../i18n/locales"),
+    },
   },
   test: {
     environment: "jsdom",