RTL and localization setup

import 'package:flutter/widgets.dart';

class AppStrings {
  AppStrings(this.locale);
  final Locale locale;

  static const supported = [Locale('en'), Locale('ar')];
  static const _table = <String, Map<String, String>>{
    'en': {'book': 'Book now', 'greeting': 'Hello, {name}'},
    'ar': {'book': 'احجز الآن', 'greeting': 'مرحبا، {name}'},
  };

  static AppStrings of(BuildContext c) => Localizations.of<AppStrings>(c, AppStrings)!;

  String _t(String k) => _table[locale.languageCode]?[k] ?? _table['en']![k]!;
  String get book => _t('book');
  String greeting(String name) => _t('greeting').replaceAll('{name}', name);

  static const delegate = _Delegate();
}

class _Delegate extends LocalizationsDelegate<AppStrings> {
  const _Delegate();
  @override
  bool isSupported(Locale l) => AppStrings.supported.any((s) => s.languageCode == l.languageCode);
  @override
  Future<AppStrings> load(Locale l) async => AppStrings(l); // synchronous table
  @override
  bool shouldReload(_Delegate old) => false;
}

import 'package:flutter/material.dart';
import 'package:flutter_localizations/flutter_localizations.dart';
import 'app_strings.dart';

class LanguageApp extends StatefulWidget {
  const LanguageApp({super.key});
  static void setLocale(BuildContext c, Locale l) {
    final state = c.findAncestorStateOfType<_LanguageAppState>()!;
    // ignore: invalid_use_of_protected_member
    state.setState(() => state._locale = l);
  }

  @override
  State<LanguageApp> createState() => _LanguageAppState();
}

class _LanguageAppState extends State<LanguageApp> {
  Locale? _locale; // null follows the device language

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      locale: _locale,
      supportedLocales: AppStrings.supported,
      localizationsDelegates: const [
        AppStrings.delegate,
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate, // supplies text direction
        GlobalCupertinoLocalizations.delegate,
      ],
      home: const _Home(),
    );
  }
}

class _Home extends StatelessWidget {
  const _Home();
  @override
  Widget build(BuildContext context) {
    final s = AppStrings.of(context);
    return Scaffold(
      appBar: AppBar(title: Text(s.greeting('Sam')), actions: [
        TextButton(onPressed: () => LanguageApp.setLocale(context, const Locale('ar')), child: const Text('AR')),
        TextButton(onPressed: () => LanguageApp.setLocale(context, const Locale('en')), child: const Text('EN')),
      ]),
      // Padding and alignment use Directional types so they mirror in RTL.
      body: Padding(
        padding: const EdgeInsetsDirectional.only(start: 24, top: 24),
        child: Align(alignment: AlignmentDirectional.topStart, child: FilledButton(onPressed: () {}, child: Text(s.book))),
      ),
    );
  }
}