fix(mobile): fallback localizations for unsupported locales

mobile/lib/main.dart

@@ -40,6 +40,7 @@ import 'package:immich_mobile/theme/theme_data.dart';
 import 'package:immich_mobile/utils/bootstrap.dart';
 import 'package:immich_mobile/utils/cache/widgets_binding.dart';
 import 'package:immich_mobile/utils/debug_print.dart';
+import 'package:immich_mobile/utils/fallback_localizations.dart';
 import 'package:immich_mobile/utils/licenses.dart';
 import 'package:immich_mobile/utils/migration.dart';
 import 'package:immich_mobile/wm_executor.dart';
@@ -283,7 +284,7 @@ class ImmichAppState extends ConsumerState<ImmichApp> with WidgetsBindingObserve
         title: 'Immich',
         debugShowCheckedModeBanner: true,
         scaffoldMessengerKey: scaffoldMessengerKey,
-        localizationsDelegates: context.localizationDelegates,
+        localizationsDelegates: [...context.localizationDelegates, ...fallbackLocalizationDelegates],
         supportedLocales: context.supportedLocales,
         locale: context.locale,
         themeMode: ref.watch(appConfigProvider.select((config) => config.theme.mode)),

mobile/lib/pages/common/splash_screen.page.dart

@@ -24,6 +24,7 @@ import 'package:immich_mobile/providers/websocket.provider.dart';
 import 'package:immich_mobile/routing/router.dart';
 import 'package:immich_mobile/theme/color_scheme.dart';
 import 'package:immich_mobile/theme/theme_data.dart';
+import 'package:immich_mobile/utils/fallback_localizations.dart';
 import 'package:immich_mobile/widgets/common/immich_logo.dart';
 import 'package:immich_mobile/widgets/common/immich_title_text.dart';
 import 'package:logging/logging.dart';
@@ -49,7 +50,7 @@ class BootstrapErrorWidget extends StatelessWidget {
         builder: (lCtx) => MaterialApp(
           title: 'Immich',
           debugShowCheckedModeBanner: true,
-          localizationsDelegates: lCtx.localizationDelegates,
+          localizationsDelegates: [...lCtx.localizationDelegates, ...fallbackLocalizationDelegates],
           supportedLocales: lCtx.supportedLocales,
           locale: lCtx.locale,
           themeMode: ThemeMode.system,

mobile/lib/utils/fallback_localizations.dart

@@ -0,0 +1,23 @@
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+
+// Flutter ships no Material or Cupertino strings for some of our languages, use English for those
+const List<LocalizationsDelegate> fallbackLocalizationDelegates = [
+  _FallbackLocalizationsDelegate<MaterialLocalizations>(DefaultMaterialLocalizations.delegate),
+  _FallbackLocalizationsDelegate<CupertinoLocalizations>(DefaultCupertinoLocalizations.delegate),
+];
+
+class _FallbackLocalizationsDelegate<T> extends LocalizationsDelegate<T> {
+  final LocalizationsDelegate<T> delegate;
+
+  const _FallbackLocalizationsDelegate(this.delegate);
+
+  @override
+  bool isSupported(Locale locale) => true;
+
+  @override
+  Future<T> load(Locale locale) => delegate.load(locale);
+
+  @override
+  bool shouldReload(_FallbackLocalizationsDelegate<T> old) => false;
+}

mobile/test/utils/fallback_localizations_test.dart

@@ -0,0 +1,17 @@
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../widget_tester_extensions.dart';
+
+void main() {
+  testWidgets('Material and Cupertino widgets work in languages Flutter has no translations for', (tester) async {
+    await tester.pumpConsumerWidget(
+      const Column(children: [BackButton(), CupertinoSearchTextField()]),
+      locale: const Locale('mi'),
+    );
+
+    expect(find.byTooltip('Back'), findsOneWidget);
+    expect(find.text('Search'), findsOneWidget);
+  });
+}

mobile/test/widget_tester_extensions.dart

@@ -4,6 +4,7 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:hooks_riverpod/hooks_riverpod.dart';
 import 'package:immich_mobile/constants/locales.dart';
 import 'package:immich_mobile/generated/codegen_loader.g.dart';
+import 'package:immich_mobile/utils/fallback_localizations.dart';
 
 extension PumpConsumerWidget on WidgetTester {
   /// Wraps the provided [widget] with a localized Material app such that it
@@ -20,12 +21,13 @@ extension PumpConsumerWidget on WidgetTester {
     Duration? duration,
     EnginePhase phase = EnginePhase.sendSemanticsUpdate,
     List<Override> overrides = const [],
+    Locale? locale,
   }) async {
     await pumpWidget(
       EasyLocalization(
         supportedLocales: locales.values.toList(),
         path: translationsPath,
-        startLocale: locales.values.first,
+        startLocale: locale ?? locales.values.first,
         fallbackLocale: locales.values.first,
         saveLocale: false,
         useFallbackTranslations: true,
@@ -35,7 +37,7 @@ extension PumpConsumerWidget on WidgetTester {
           child: Builder(
             builder: (context) => MaterialApp(
               debugShowCheckedModeBanner: false,
-              localizationsDelegates: context.localizationDelegates,
+              localizationsDelegates: [...context.localizationDelegates, ...fallbackLocalizationDelegates],
               supportedLocales: context.supportedLocales,
               locale: context.locale,
               home: Material(child: widget),