diff --git a/src/main/api/dto/folders.ts b/src/main/api/dto/folders.ts
index 6ce8dade5..14715706e 100644
--- a/src/main/api/dto/folders.ts
+++ b/src/main/api/dto/folders.ts
@@ -14,6 +14,12 @@ const foldersUpdate = t.Object({
   orderIndex: t.Optional(t.Number()),
 })
 
+const foldersDefaultLanguageUpdate = t.Object({
+  language: t.String(),
+  updateDescendantFolders: t.Boolean(),
+  updateSnippetContents: t.Boolean(),
+})
+
 const foldersItem = t.Object({
   id: t.Number(),
   name: t.String(),
@@ -38,6 +44,7 @@ const foldersTreeResponse = t.Array(foldersItemWithChildren)
 
 export const foldersDTO = new Elysia().model({
   foldersAdd,
+  foldersDefaultLanguageUpdate,
   foldersResponse,
   foldersUpdate,
   foldersTreeResponse,
diff --git a/src/main/api/routes/folders.ts b/src/main/api/routes/folders.ts
index 354cc4a66..bebd87242 100644
--- a/src/main/api/routes/folders.ts
+++ b/src/main/api/routes/folders.ts
@@ -149,6 +149,33 @@ app
       },
     },
   )
+  .patch(
+    '/:id/default-language',
+    ({ params, body, status }) => {
+      const storage = useStorage()
+      try {
+        const { notFound } = storage.folders.updateFolderDefaultLanguage(
+          Number(params.id),
+          body,
+        )
+
+        if (notFound) {
+          return status(404, { message: 'Folder not found' })
+        }
+
+        return { message: 'Folder language updated' }
+      }
+      catch (error) {
+        return mapStorageError(status, error)
+      }
+    },
+    {
+      body: 'foldersDefaultLanguageUpdate',
+      detail: {
+        tags: ['Folders'],
+      },
+    },
+  )
   // Удаление папки
   .delete(
     '/:id',
diff --git a/src/main/i18n/locales/en_US/ui.json b/src/main/i18n/locales/en_US/ui.json
index a842fea1d..c8940af86 100644
--- a/src/main/i18n/locales/en_US/ui.json
+++ b/src/main/i18n/locales/en_US/ui.json
@@ -1197,6 +1197,11 @@
   },
   "folder": {
     "untitled": "Untitled folder",
+    "defaultLanguageDialog": {
+      "title": "Update nested content",
+      "descendantFolders": "Update the default language for all nested folders",
+      "snippetContents": "Update the language for all nested snippet contents"
+    },
     "iconPicker": {
       "searchPlaceholder": "Search icons...",
       "emojiSearchPlaceholder": "Search emoji...",
@@ -1242,6 +1247,7 @@
     "back": "Back",
     "cancel": "Cancel",
     "confirm": "Confirm",
+    "yes": "Yes",
     "copy": "Copy",
     "fit": "Fit",
     "generate": "Generate",
diff --git a/src/main/i18n/locales/ru_RU/ui.json b/src/main/i18n/locales/ru_RU/ui.json
index 2f546d1b1..10bdfc54f 100644
--- a/src/main/i18n/locales/ru_RU/ui.json
+++ b/src/main/i18n/locales/ru_RU/ui.json
@@ -1200,6 +1200,11 @@
   },
   "folder": {
     "untitled": "Папка без названия",
+    "defaultLanguageDialog": {
+      "title": "Обновить вложенные файлы",
+      "descendantFolders": "Обновить язык по умолчанию для всех вложенных папок",
+      "snippetContents": "Обновить язык для всех вложенных сниппетов"
+    },
     "iconPicker": {
       "searchPlaceholder": "Поиск иконок...",
       "emojiSearchPlaceholder": "Поиск эмодзи...",
@@ -1245,6 +1250,7 @@
     "back": "Назад",
     "cancel": "Отмена",
     "confirm": "Подтвердить",
+    "yes": "Да",
     "copy": "Копировать",
     "fit": "По размеру",
     "generate": "Сгенерировать",
diff --git a/src/main/storage/contracts.ts b/src/main/storage/contracts.ts
index 2a46f77c8..2abed23ad 100644
--- a/src/main/storage/contracts.ts
+++ b/src/main/storage/contracts.ts
@@ -59,11 +59,21 @@ export interface FolderUpdateResult {
   notFound: boolean
 }
 
+export interface FolderDefaultLanguageUpdateInput {
+  language: string
+  updateDescendantFolders: boolean
+  updateSnippetContents: boolean
+}
+
 export interface FoldersStorage {
   createFolder: (input: FolderCreateInput) => { id: number }
   deleteFolder: (id: number) => { deleted: boolean }
   getFolders: () => FolderRecord[]
   getFoldersTree: () => FolderTreeRecord[]
+  updateFolderDefaultLanguage: (
+    id: number,
+    input: FolderDefaultLanguageUpdateInput,
+  ) => FolderUpdateResult
   updateFolder: (id: number, input: FolderUpdateInput) => FolderUpdateResult
 }
 
diff --git a/src/main/storage/providers/markdown/storages/__tests__/folders.test.ts b/src/main/storage/providers/markdown/storages/__tests__/folders.test.ts
index ce248c601..883e89a9e 100644
--- a/src/main/storage/providers/markdown/storages/__tests__/folders.test.ts
+++ b/src/main/storage/providers/markdown/storages/__tests__/folders.test.ts
@@ -14,6 +14,7 @@ import {
 import { ensureStateFile } from '../../runtime/state'
 import { resetRuntimeCache } from '../../runtime/sync'
 import { createFoldersStorage } from '../folders'
+import { createSnippetsStorage } from '../snippets'
 
 let tempVaultPath = ''
 
@@ -138,6 +139,39 @@ describe('code folders storage validations', () => {
     expect(result).toEqual({ invalidInput: true, notFound: false })
   })
 
+  it('updates the selected folder and opted-in nested content language', () => {
+    const folders = createFoldersStorage()
+    const snippets = createSnippetsStorage()
+    const { id: parentId } = folders.createFolder({ name: 'Parent' })
+    const { id: childId } = folders.createFolder({ name: 'Child', parentId })
+    const parentSnippet = snippets.createSnippet({
+      name: 'Parent snippet',
+      folderId: parentId,
+    })
+    const childSnippet = snippets.createSnippet({
+      name: 'Child snippet',
+      folderId: childId,
+    })
+    snippets.createSnippetContent(parentSnippet.id, {
+      label: 'Fragment 1', language: 'plain_text', value: '',
+    })
+    snippets.createSnippetContent(childSnippet.id, {
+      label: 'Fragment 1', language: 'plain_text', value: '',
+    })
+
+    const result = folders.updateFolderDefaultLanguage(parentId, {
+      language: 'typescript',
+      updateDescendantFolders: true,
+      updateSnippetContents: true,
+    })
+
+    expect(result).toEqual({ invalidInput: false, notFound: false })
+    expect(folders.getFolders().find(folder => folder.id === parentId)?.defaultLanguage).toBe('typescript')
+    expect(folders.getFolders().find(folder => folder.id === childId)?.defaultLanguage).toBe('typescript')
+    expect(snippets.getSnippetById(parentSnippet.id)?.contents[0]?.language).toBe('typescript')
+    expect(snippets.getSnippetById(childSnippet.id)?.contents[0]?.language).toBe('typescript')
+  })
+
   it('moving folder into sibling level with same name auto-resolves unique name', () => {
     const storage = createFoldersStorage()
     const { id: parentId } = storage.createFolder({ name: 'Parent' })
diff --git a/src/main/storage/providers/markdown/storages/folders.ts b/src/main/storage/providers/markdown/storages/folders.ts
index 298d277da..bfbb89d8e 100644
--- a/src/main/storage/providers/markdown/storages/folders.ts
+++ b/src/main/storage/providers/markdown/storages/folders.ts
@@ -25,11 +25,13 @@ import {
   syncFolderMetadataFiles,
   throwStorageError,
   validateEntryName,
+  writeSnippetToFile,
 } from '../runtime'
 import {
   getFileAvailability,
   markAppWrittenFileAsLocal,
 } from '../runtime/shared/cloudFiles'
+import { assertEntityFileWritable } from '../runtime/shared/cloudGuards'
 import {
   applyFolderParentAndOrder,
   assertFolderMoveTargetValid,
@@ -102,6 +104,63 @@ export function createFoldersStorage(): FoldersStorage {
 
       return { id }
     },
+    updateFolderDefaultLanguage: (id, input): FolderUpdateResult => {
+      const paths = getPaths(getVaultPath())
+      const { state, snippets } = getRuntimeCache(paths)
+      const folder = findFolderById(state, id)
+
+      if (!folder) {
+        return { invalidInput: false, notFound: true }
+      }
+
+      const descendantFolderIds = collectDescendantIds(state.folders, id)
+      const contentFolderIds = new Set(descendantFolderIds)
+      contentFolderIds.add(id)
+      const snippetsToUpdate = input.updateSnippetContents
+        ? snippets.filter(
+            snippet =>
+              snippet.isDeleted !== 1
+              && snippet.folderId !== null
+              && contentFolderIds.has(snippet.folderId),
+          )
+        : []
+
+      snippetsToUpdate.forEach((snippet) => {
+        assertEntityFileWritable(
+          path.join(paths.vaultPath, snippet.filePath),
+          snippet,
+        )
+      })
+
+      const now = Date.now()
+      folder.defaultLanguage = input.language || folder.defaultLanguage
+      folder.updatedAt = now
+
+      if (input.updateDescendantFolders) {
+        state.folders.forEach((childFolder) => {
+          if (!descendantFolderIds.has(childFolder.id)) {
+            return
+          }
+
+          childFolder.defaultLanguage
+            = input.language || childFolder.defaultLanguage
+          childFolder.updatedAt = now
+        })
+      }
+
+      snippetsToUpdate.forEach((snippet) => {
+        snippet.contents.forEach((content) => {
+          content.language = input.language || content.language
+        })
+        snippet.updatedAt = now
+        writeSnippetToFile(paths, snippet)
+      })
+
+      syncFolderMetadataFiles(paths, state)
+      saveState(paths, state)
+
+      return { invalidInput: false, notFound: false }
+    },
     updateFolder: (id, input): FolderUpdateResult => {
       const paths = getPaths(getVaultPath())
 
diff --git a/src/renderer/components/sidebar/folders/DefaultLanguageUpdateDialog.vue b/src/renderer/components/sidebar/folders/DefaultLanguageUpdateDialog.vue
new file mode 100644
index 000000000..170c596cc
--- /dev/null
+++ b/src/renderer/components/sidebar/folders/DefaultLanguageUpdateDialog.vue
@@ -0,0 +1,56 @@
+<script setup lang="ts">
+import { Checkbox } from '@/components/ui/shadcn/checkbox'
+import * as Dialog from '@/components/ui/shadcn/dialog'
+import { i18n } from '@/electron'
+
+interface Props {
+  hasDescendantFolders: boolean
+  hasSnippetContents: boolean
+}
+
+const props = defineProps<Props>()
+const open = defineModel<boolean>('open', { required: true })
+const emit = defineEmits<{
+  confirm: [options: { updateDescendantFolders: boolean, updateSnippetContents: boolean }]
+}>()
+const updateDescendantFolders = ref(false)
+const updateSnippetContents = ref(false)
+
+function confirm() {
+  emit('confirm', {
+    updateDescendantFolders: updateDescendantFolders.value,
+    updateSnippetContents: updateSnippetContents.value,
+  })
+}
+
+watch(open, (isOpen) => {
+  if (!isOpen) {
+    updateDescendantFolders.value = false
+    updateSnippetContents.value = false
+  }
+})
+</script>
+
+<template>
+  <Dialog.Dialog v-model:open="open">
+    <Dialog.DialogContent class="cursor-default sm:max-w-[425px]">
+      <Dialog.DialogHeader>
+        <Dialog.DialogTitle>{{ i18n.t('folder.defaultLanguageDialog.title') }}</Dialog.DialogTitle>
+      </Dialog.DialogHeader>
+      <div class="space-y-3">
+        <label v-if="props.hasDescendantFolders" class="flex cursor-pointer items-center gap-2">
+          <Checkbox v-model="updateDescendantFolders" />
+          <UiText as="span">{{ i18n.t('folder.defaultLanguageDialog.descendantFolders') }}</UiText>
+        </label>
+        <label v-if="props.hasSnippetContents" class="flex cursor-pointer items-center gap-2">
+          <Checkbox v-model="updateSnippetContents" />
+          <UiText as="span">{{ i18n.t('folder.defaultLanguageDialog.snippetContents') }}</UiText>
+        </label>
+      </div>
+      <Dialog.DialogFooter>
+        <UiButton class="cursor-pointer" variant="outline" @click="open = false">{{ i18n.t('button.cancel') }}</UiButton>
+        <UiButton class="cursor-pointer" @click="confirm">{{ i18n.t('button.yes') }}</UiButton>
+      </Dialog.DialogFooter>
+    </Dialog.DialogContent>
+  </Dialog.Dialog>
+</template>
diff --git a/src/renderer/components/sidebar/folders/Tree.vue b/src/renderer/components/sidebar/folders/Tree.vue
index 590fb9f16..416fe02a2 100644
--- a/src/renderer/components/sidebar/folders/Tree.vue
+++ b/src/renderer/components/sidebar/folders/Tree.vue
@@ -19,6 +19,7 @@ import {
   getEntryNameConflictMessage,
   getEntryNameValidationMessage,
 } from '@/utils'
+import { api } from '@/services/api'
 import { Folder } from 'lucide-vue-next'
 import CustomIcons from './custom-icons/CustomIcons.vue'
 
@@ -45,6 +46,7 @@ const {
   deleteSelectedFolders,
   folders,
   updateFolder,
+  updateFolderDefaultLanguage,
   getFolderByIdFromTree,
   getFolders,
   selectedFolderIds,
@@ -115,6 +117,10 @@ const highlightedIds = computed({
 // --- Context menu state ---
 
 const contextNode = ref<Node | null>(null)
+const isDefaultLanguageDialogOpen = ref(false)
+const pendingDefaultLanguage = ref<string | null>(null)
+const hasDescendantFolders = ref(false)
+const hasSnippetContents = ref(false)
 
 const isContextMultiSelection = computed(() => {
   if (!contextNode.value)
@@ -304,10 +310,47 @@ function onRenameFolder() {
   }, 100)
 }
 
-function onSelectLanguage(language: string) {
+async function onSelectLanguage(language: string) {
   if (!contextNode.value)
     return
-  updateFolder(contextNode.value.id, { defaultLanguage: language })
+
+  const folderIds = flattenFolders([contextNode.value]).map(folder => folder.id)
+  hasDescendantFolders.value = folderIds.length > 1
+  const { data: snippets } = await api.snippets.getSnippets({})
+  hasSnippetContents.value = snippets.some(
+    snippet =>
+      !snippet.isDeleted
+      && snippet.folder
+      && folderIds.includes(snippet.folder.id)
+      && snippet.contents.length > 0,
+  )
+
+  if (!hasDescendantFolders.value && !hasSnippetContents.value) {
+    await updateFolderDefaultLanguage(contextNode.value.id, {
+      language,
+      updateDescendantFolders: false,
+      updateSnippetContents: false,
+    })
+    return
+  }
+
+  pendingDefaultLanguage.value = language
+  isDefaultLanguageDialogOpen.value = true
+}
+
+async function onConfirmDefaultLanguageUpdate(options: {
+  updateDescendantFolders: boolean
+  updateSnippetContents: boolean
+}) {
+  if (!contextNode.value || !pendingDefaultLanguage.value)
+    return
+
+  await updateFolderDefaultLanguage(contextNode.value.id, {
+    language: pendingDefaultLanguage.value,
+    ...options,
+  })
+  isDefaultLanguageDialogOpen.value = false
+  pendingDefaultLanguage.value = null
 }
 
 function scrollToSelectedLanguage(el: any, isSelected: boolean) {
@@ -369,6 +412,12 @@ useDeleteShortcut({
     data-code-folders-tree
     class="h-full min-h-0"
   >
+    <SidebarFoldersDefaultLanguageUpdateDialog
+      v-model:open="isDefaultLanguageDialogOpen"
+      :has-descendant-folders="hasDescendantFolders"
+      :has-snippet-contents="hasSnippetContents"
+      @confirm="onConfirmDefaultLanguageUpdate"
+    />
     <ContextMenu.ContextMenu>
       <ContextMenu.ContextMenuTrigger as-child>
         <UiTree
@@ -455,7 +504,7 @@ useDeleteShortcut({
                         contextNodeDefaultLanguage === language.value,
                       )
                   "
-                  :checked="contextNodeDefaultLanguage === language.value"
+                  :model-value="contextNodeDefaultLanguage === language.value"
                   @click="onSelectLanguage(language.value)"
                 >
                   {{ language.name }}
diff --git a/src/renderer/composables/useFolders.ts b/src/renderer/composables/useFolders.ts
index 89761a291..2a81acdef 100644
--- a/src/renderer/composables/useFolders.ts
+++ b/src/renderer/composables/useFolders.ts
@@ -391,6 +391,30 @@ async function updateFolder(folderId: number, data: FoldersUpdate) {
   }
 }
 
+async function updateFolderDefaultLanguage(
+  folderId: number,
+  data: {
+    language: string
+    updateDescendantFolders: boolean
+    updateSnippetContents: boolean
+  },
+) {
+  try {
+    markPersistedStorageMutation()
+    await api.folders.patchFoldersByIdDefaultLanguage(String(folderId), data)
+    await getFolders(false)
+
+    const { getSnippets, refreshSelectedSnippet } = useSnippets()
+    if (folderId === state.folderId) {
+      await getSnippets({ folderId })
+    }
+    await refreshSelectedSnippet()
+  }
+  catch (error) {
+    console.error(error)
+  }
+}
+
 async function deleteFolder(folderId: number, shouldRefresh = true) {
   try {
     markPersistedStorageMutation()
@@ -513,5 +537,6 @@ export function useFolders() {
     setFolderSelection,
     selectFolder,
     updateFolder,
+    updateFolderDefaultLanguage,
   }
 }
diff --git a/src/renderer/services/api/generated/index.ts b/src/renderer/services/api/generated/index.ts
index c1fcba36d..7f9875fe5 100644
--- a/src/renderer/services/api/generated/index.ts
+++ b/src/renderer/services/api/generated/index.ts
@@ -155,6 +155,12 @@ export interface FoldersAdd {
   parentId?: number | null;
 }
 
+export interface FoldersDefaultLanguageUpdate {
+  language: string;
+  updateDescendantFolders: boolean;
+  updateSnippetContents: boolean;
+}
+
 export type FoldersResponse = {
   id: number;
   name: string;
@@ -2165,6 +2171,26 @@ export class Api<
         ...params,
       }),
 
+    /**
+     * No description
+     *
+     * @tags Folders
+     * @name PatchFoldersByIdDefaultLanguage
+     * @request PATCH:/folders/{id}/default-language
+     */
+    patchFoldersByIdDefaultLanguage: (
+      id: string,
+      data: FoldersDefaultLanguageUpdate,
+      params: RequestParams = {},
+    ) =>
+      this.request<void, any>({
+        path: `/folders/${id}/default-language`,
+        method: "PATCH",
+        body: data,
+        type: ContentType.Json,
+        ...params,
+      }),
+
     /**
      * No description
      *