diff --git a/web/src/lib/components/shared-components/settings/SettingsLanguageSelector.svelte b/web/src/lib/components/shared-components/settings/SettingsLanguageSelector.svelte
index 269edb2204..146c37b7ec 100644
--- a/web/src/lib/components/shared-components/settings/SettingsLanguageSelector.svelte
+++ b/web/src/lib/components/shared-components/settings/SettingsLanguageSelector.svelte
@@ -3,7 +3,7 @@
   import Combobox from '$lib/components/shared-components/Combobox.svelte';
   import { defaultLang } from '$lib/constants';
   import { lang } from '$lib/stores/preferences.store';
-  import { getClosestAvailableLocale, langCodes, langs } from '$lib/utils/i18n';
+  import { convertBCP47, getClosestAvailableLocale, langCodes, langs } from '$lib/utils/i18n';
   import { Label, Text } from '@immich/ui';
   import { locale as i18nLocale, t } from 'svelte-i18n';
 
@@ -13,14 +13,14 @@
 
   let { showSettingDescription = false }: Props = $props();
 
-  const langOptions = langs.map((lang) => ({ label: lang.name, value: lang.code }));
+  const langOptions = langs.map((lang) => ({ label: lang.name, value: convertBCP47(lang.code) }));
 
   const defaultLangOption = { label: defaultLang.name, value: defaultLang.code };
 
   const handleLanguageChange = async (newLang: string | undefined) => {
     if (newLang) {
       $lang = newLang;
-      await i18nLocale.set(newLang);
+      await i18nLocale.set(convertBCP47(newLang));
       await invalidateAll();
     }
   };
diff --git a/web/src/lib/stores/preferences.store.ts b/web/src/lib/stores/preferences.store.ts
index d08dfc0475..2584312220 100644
--- a/web/src/lib/stores/preferences.store.ts
+++ b/web/src/lib/stores/preferences.store.ts
@@ -1,12 +1,12 @@
 import { persisted } from 'svelte-persisted-store';
 import { browser } from '$app/environment';
 import { defaultLang } from '$lib/constants';
-import { getPreferredLocale } from '$lib/utils/i18n';
+import { convertBCP47, getPreferredLocale } from '$lib/utils/i18n';
 
 // Locale to use for formatting dates, numbers, etc.
 export const locale = persisted('locale', 'default', {
   serializer: {
-    parse: (text) => text || 'default',
+    parse: (text) => convertBCP47(text) || 'default',
     stringify: (object) => object ?? '',
   },
 });
@@ -14,7 +14,7 @@ export const locale = persisted('locale', 'default', {
 const preferredLocale = browser ? getPreferredLocale() : undefined;
 export const lang = persisted<string>('lang', preferredLocale || defaultLang.code, {
   serializer: {
-    parse: (text) => text,
+    parse: (text) => convertBCP47(text),
     stringify: (object) => object ?? '',
   },
 });
diff --git a/web/src/lib/utils.ts b/web/src/lib/utils.ts
index 4ff3564ffa..0e31782164 100644
--- a/web/src/lib/utils.ts
+++ b/web/src/lib/utils.ts
@@ -28,7 +28,7 @@ import { downloadManager } from '$lib/managers/download-manager.svelte';
 import { alwaysLoadOriginalFile, lang } from '$lib/stores/preferences.store';
 import { isWebCompatibleImage } from '$lib/utils/asset-utils';
 import { handleError } from '$lib/utils/handle-error';
-import { langs } from '$lib/utils/i18n';
+import { convertBCP47, langs } from '$lib/utils/i18n';
 
 interface DownloadRequestOptions<T = unknown> {
   method?: 'GET' | 'POST' | 'PUT' | 'DELETE';
@@ -47,7 +47,7 @@ interface DateFormatter {
 export const initLanguage = async () => {
   const preferenceLang = get(lang);
   for (const { code, loader } of langs) {
-    register(code, loader);
+    register(convertBCP47(code), loader);
   }
 
   await init({ fallbackLocale: preferenceLang === 'dev' ? 'dev' : defaultLang.code, initialLocale: preferenceLang });
diff --git a/web/src/lib/utils/i18n.ts b/web/src/lib/utils/i18n.ts
index d179efb5bd..85331ddf7c 100644
--- a/web/src/lib/utils/i18n.ts
+++ b/web/src/lib/utils/i18n.ts
@@ -19,7 +19,7 @@ const fileCodes = Object.keys(modules)
   .map((path) => path.match(/\/(\w+)\.json$/)?.[1])
   .filter(Boolean) as string[];
 
-const convertBCP47 = (code: string) => code.replaceAll('_', '-');
+export const convertBCP47 = (code: string) => code.replaceAll('_', '-');
 
 export const langCodes = fileCodes.map((code) => convertBCP47(code));