diff --git a/apps/rebreak-native/stores/auth.ts b/apps/rebreak-native/stores/auth.ts
index 584527a..17d4de7 100644
--- a/apps/rebreak-native/stores/auth.ts
+++ b/apps/rebreak-native/stores/auth.ts
@@ -7,6 +7,7 @@ import * as AppleAuthentication from 'expo-apple-authentication';
 import { supabase } from '../lib/supabase';
 import { apiFetch } from '../lib/api';
 import i18n from '../lib/i18n';
+import { syncLanguageFromUserMetadata } from './language';
 
 const SUPPORTED_LOCALES = ['de', 'en', 'fr', 'ar'] as const;
 type SupportedLocale = (typeof SUPPORTED_LOCALES)[number];
@@ -69,9 +70,15 @@ export const useAuthStore = create<AuthState>((set) => ({
       user: data.session?.user ?? null,
       loading: false,
     });
+    if (data.session?.user) {
+      void syncLanguageFromUserMetadata(data.session.user);
+    }
 
     supabase.auth.onAuthStateChange((_event, session) => {
       set({ session, user: session?.user ?? null });
+      if (session?.user) {
+        void syncLanguageFromUserMetadata(session.user);
+      }
     });
   },
 
diff --git a/apps/rebreak-native/stores/language.ts b/apps/rebreak-native/stores/language.ts
index 6aef435..a21af21 100644
--- a/apps/rebreak-native/stores/language.ts
+++ b/apps/rebreak-native/stores/language.ts
@@ -61,3 +61,32 @@ export const useLanguageStore = create<LanguageState>((set) => ({
     }
   },
 }));
+
+// Auto-sync language from session.user.user_metadata.locale beim Sign-In.
+// Wenn AsyncStorage @rebreak/language LEER ist (kein explicit user-choice)
+// und Server-side metadata.locale gesetzt — silent apply (kein Restart-Alert).
+// Respektiert User-Choice: AsyncStorage gewinnt immer wenn gesetzt.
+export async function syncLanguageFromUserMetadata(
+  user: { user_metadata?: { locale?: string | null } | null } | null,
+): Promise<void> {
+  if (!user) return;
+  const raw = user.user_metadata?.locale;
+  if (!raw) return;
+  const short = String(raw).split('-')[0].toLowerCase();
+  const valid: AppLanguage[] = ['de', 'en', 'fr', 'ar'];
+  if (!(valid as readonly string[]).includes(short)) return;
+  const lang = short as AppLanguage;
+
+  const stored = await AsyncStorage.getItem(STORAGE_KEY);
+  if (stored) return; // explicit user-choice wins
+
+  if (i18n.language === lang) {
+    await AsyncStorage.setItem(STORAGE_KEY, lang);
+    return;
+  }
+
+  await AsyncStorage.setItem(STORAGE_KEY, lang);
+  await i18n.changeLanguage(lang);
+  applyRTL(lang);
+  useLanguageStore.setState({ language: lang });
+}