diff --git a/lib/utils/l10n.spec.ts b/lib/utils/l10n.spec.ts
index 4852ee5f4..af3e91915 100644
--- a/lib/utils/l10n.spec.ts
+++ b/lib/utils/l10n.spec.ts
@@ -13,3 +13,10 @@ test('translation compressing and decompressing is working', async () => {
 	const { t } = await import('./l10n.ts')
 	expect(t('Names must not be empty.')).toMatchInlineSnapshot('"Namen dürfen nicht leer sein."')
 })
+
+// if a language is not available, it should fall back to the base language (e.g. ja-JP -> ja)
+test('properly falls back to base language', async () => {
+	setLanguage('ja')
+	const { t } = await import('./l10n.ts')
+	expect(t('Names must not be empty.')).toMatchInlineSnapshot('"名前は空にできません。"')
+})
diff --git a/lib/utils/l10n.ts b/lib/utils/l10n.ts
index 3b5ef4261..0ca9603d1 100644
--- a/lib/utils/l10n.ts
+++ b/lib/utils/l10n.ts
@@ -5,20 +5,30 @@
 
 import type { GettextTranslation, GettextTranslationBundle } from '@nextcloud/l10n/gettext'
 
+import { getLanguage } from '@nextcloud/l10n'
 import { getGettextBuilder } from '@nextcloud/l10n/gettext'
 
+const currentLanguage = getLanguage().replace('-', '_')
 const gtBuilder = getGettextBuilder()
-	.detectLanguage()
+	.setLanguage(currentLanguage)
 
-for (const data of __TRANSLATIONS__) {
+// eslint-disable-next-line @stylistic/semi
+const translations = __TRANSLATIONS__;
+
+const languages = translations.map(({ language }) => language)
+const useBaseLanguage = !languages.includes(currentLanguage)
+for (const data of translations) {
 	const { language, translations } = data as { language: string, translations: GettextTranslation[] }
-	const bundle: GettextTranslationBundle = {
-		headers: {},
-		translations: {
-			'': Object.fromEntries(translations.map((translation: GettextTranslation) => [translation.msgid, translation])),
-		},
+	const needsRename = useBaseLanguage && currentLanguage === language.split('_')[0]
+	if (language === currentLanguage || language === 'en' || needsRename) {
+		const bundle: GettextTranslationBundle = {
+			headers: {},
+			translations: {
+				'': Object.fromEntries(translations.map((translation: GettextTranslation) => [translation.msgid, translation])),
+			},
+		}
+		gtBuilder.addTranslation(needsRename ? currentLanguage : language, bundle)
 	}
-	gtBuilder.addTranslation(language, bundle)
 }
 
 const gt = gtBuilder.build()