How to persist selected language in Flutter? 

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart';

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final prefs = await SharedPreferences.getInstance();

  runApp(MyApp(prefs: prefs));
}

class MyApp extends StatelessWidget {
  final SharedPreferences _prefs;

  const MyApp({Key? key, required SharedPreferences prefs})
      : _prefs = prefs,
        super(key: key);

  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      create: (context) => LocaleModel(_prefs),
      child: Consumer<LocaleModel>(
        builder: (context, localeModel, child) => MaterialApp(
          title: 'Your app title',
          localizationsDelegates: AppLocalizations.localizationsDelegates,
          supportedLocales: AppLocalizations.supportedLocales,
          locale: localeModel.locale,
          /* ... */
        ),
      ),
    );
  }
}

class LocaleModel extends ChangeNotifier {
  Locale? _locale;
  final SharedPreferences _prefs;

  LocaleModel(this._prefs) {
    var selectedLocale = _prefs.getString("selectedLocale");
    if (selectedLocale != null) {
      _locale = Locale(selectedLocale);
    }
  }

  Locale? get locale => _locale;

  void set(Locale locale) {
    _locale = locale;
    _prefs.setString('selectedLocale', locale.toString());

    notifyListeners();
  }
}