Flutter code sample to manage localization using riverpod

riverpod_localization_sample.dart

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

class LocalizationNotifier extends StateNotifier<Locale?> {
  LocalizationNotifier({
    required this.defaultLocale,
    required this.supportedLocales,
  }) : super(defaultLocale);

  final Locale defaultLocale;
  final List<Locale> supportedLocales;

  Future<void> loadLocale() async {
    // Load the locale from the storage, then set the state accordingly.
    state = const Locale('en');
  }

  Future<void> setLocale(Locale locale) async {
    if (!supportedLocales.contains(locale)) return;
    
    // Save your locale for future usage then set the state.
    state = locale;
  }
}

final localizationProvider =
    StateNotifierProvider.autoDispose<LocalizationNotifier, Locale?>(
  (ref) {
    final defaultLocale = ref.watch(defaultLocaleProvider);
    final supportedLocales = ref.watch(supportedLocalesProvider);

    return LocalizationNotifier(
      defaultLocale: defaultLocale,
      supportedLocales: supportedLocales,
    );
  },
);

final supportedLocalesProvider = Provider<List<Locale>>(
  (ref) => const [Locale('fr'), Locale('en')],
);

final defaultLocaleProvider = Provider<Locale>(
  (ref) => const Locale('en'),
);

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();

  final container = ProviderContainer();
  final localizationNotifier = container.read(localizationProvider.notifier);
  await localizationNotifier.loadLocale();

  runApp(
    UncontrolledProviderScope(
      container: container,
      child: MyApp(),
    ),
  );
}

class MyApp extends ConsumerWidget {
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final locale = ref.watch(localizationProvider);
    final supportedLocales = ref.watch(supportedLocalesProvider);

    return MaterialApp(
      locale: locale,
      supportedLocales: supportedLocales,
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        floatingActionButton: FloatingActionButton(
          onPressed: () {
            ref
                .read(localizationProvider.notifier)
                .setLocale(const Locale('fr'));
          },
          child: const Text('fr'),
        ),
        body: const Center(
          child: MyWidget(),
        ),
      ),
    );
  }
}

class MyWidget extends StatelessWidget {
  const MyWidget({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Text(Localizations.localeOf(context).toString());
  }
}