dependencies:
  flutter:
    sdk: flutter
  flutter_localizations:
    sdk: flutter
  intl: any

flutter pub add flutter_localizations --sdk=flutter
flutter pub add intl:any

flutter:
  generate: true

arb-dir: lib/l10n
template-arb-file: app_en.arb
output-localization-file: app_localizations.dart

{
  "helloWorld": "Hello World!",
  "@helloWorld": {
    "description": "Greeting message"
  }
}

{
  "helloWorld": "¡Hola Mundo!"
}

flutter gen-l10n

flutter run

import 'package:flutter/material.dart';
import 'package:flutter_localizations/flutter_localizations.dart';
import 'l10n/app_localizations.dart';

MaterialApp(
  localizationsDelegates: [
    AppLocalizations.delegate,
    GlobalMaterialLocalizations.delegate,
    GlobalWidgetsLocalizations.delegate,
    GlobalCupertinoLocalizations.delegate,
  ],
  supportedLocales: [
    Locale('en'),
    Locale('es'),
  ],
  home: MyHomePage(),
)

Text(AppLocalizations.of(context)!.helloWorld)

{
  "welcome": "Welcome to our app",
  "@welcome": {
    "description": "Welcome message"
  }
}

{
  "greeting": "Hello {userName}!",
  "@greeting": {
    "description": "Personalized greeting",
    "placeholders": {
      "userName": {
        "type": "String",
        "example": "Alice"
      }
    }
  }
}

Text(AppLocalizations.of(context)!.greeting('Alice'))

{
  "itemCount": "{count, plural, =0{No items} =1{1 item} other{{count} items}}",
  "@itemCount": {
    "placeholders": {
      "count": {
        "type": "int"
      }
    }
  }
}

Text(AppLocalizations.of(context)!.itemCount(5))

{
  "pronoun": "{gender, select, male{he} female{she} other{they}}",
  "@pronoun": {
    "placeholders": {
      "gender": {
        "type": "String"
      }
    }
  }
}

Text(AppLocalizations.of(context)!.pronoun('male'))

{
  "price": "Price: {value}",
  "@price": {
    "placeholders": {
      "value": {
        "type": "int",
        "format": "simpleCurrency"
      }
    }
  }
}

{
  "eventDate": "Event on {date}",
  "@eventDate": {
    "placeholders": {
      "date": {
        "type": "DateTime",
        "format": "yMMMd"
      }
    }
  }
}

Localizations.override(
  context: context,
  locale: const Locale('es'),
  child: CalendarDatePicker(...),
)

supportedLocales: [
  Locale.fromSubtags(languageCode: 'zh'),
  Locale.fromSubtags(languageCode: 'zh', scriptCode: 'Hans'),
  Locale.fromSubtags(languageCode: 'zh', scriptCode: 'Hant', countryCode: 'TW'),
]

MaterialApp(
  localeResolutionCallback: (locale, supportedLocales) {
    // Always accept user's locale
    return locale;
  },
)

Locale myLocale = Localizations.localeOf(context);

class DemoLocalizations {
  DemoLocalizations(this.localeName);

  static Future<DemoLocalizations> load(Locale locale) {
    final String name = Intl.canonicalizedLocale(locale.toString());
    return initializeMessages(name).then((_) => DemoLocalizations(name));
  }

  static DemoLocalizations of(BuildContext context) {
    return Localizations.of<DemoLocalizations>(context, DemoLocalizations)!;
  }

  String get title {
    return Intl.message(
      'Hello World',
      name: 'title',
      desc: 'Title',
      locale: localeName,
    );
  }
}

class DemoLocalizationsDelegate extends LocalizationsDelegate<DemoLocalizations> {
  const DemoLocalizationsDelegate();

  @override
  bool isSupported(Locale locale) => ['en', 'es'].contains(locale.languageCode);

  @override
  Future<DemoLocalizations> load(Locale locale) => DemoLocalizations.load(locale);

  @override
  bool shouldReload(DemoLocalizationsDelegate old) => false;
}

dart run intl_translation:extract_to_arb --output-dir=lib/l10n lib/main.dart
dart run intl_translation:generate_from_arb --output-dir=lib/l10n lib/main.dart lib/l10n/intl_*.arb

class DemoLocalizations {
  DemoLocalizations(this.locale);

  final Locale locale;

  static DemoLocalizations of(BuildContext context) {
    return Localizations.of<DemoLocalizations>(context, DemoLocalizations)!;
  }

  static const _localizedValues = <String, Map<String, String>>{
    'en': {'title': 'Hello World'},
    'es': {'title': 'Hola Mundo'},
  };

  String get title {
    return _localizedValues[locale.languageCode]!['title']!;
  }
}