How to add localization to a Flutter application…

Adding dependencies:

In the pubspec.yaml file, add dependencies for localization:

dependencies:
  flutter:
    sdk: flutter

  flutter_localizations:
    sdk: flutter
  intl: ^0.18.0 # Example version, may vary

Then run flutter pub get.

Creating localization files:

Create directories for localization resources, e.g., ./lib/l10n/. Inside, create .arb files for each supported language. For example, for English and Russian:

app_en.arb:
```
{
  "helloWorld": "Hello World!",
  "@@locale": "en"
}
```
app_ru.arb:
```
{
  "helloWorld": "Привет мир!",
  "@@locale": "ru"
}
```

Configuring code generation:

In the pubspec.yaml file, specify the path to localization files and configure .arb generation:

flutter:
  generate: true # Enable generation

  assets:
    - assets/... # Your other assets

  l10n:
    arb-dir: lib/l10n # Directory with .arb files
    template-arb-file: app_en.arb # Template .arb file
    output-localization-file: app_localizations.dart # Name of generated file

After saving pubspec.yaml, Flutter will automatically generate the file ./lib/generated/l10n.dart (or the specified output-localization-file).

Using localized strings:

In the app where you need to use localized strings, import the generated file:
```
import 'package:flutter_gen/gen_l10n/app_localizations.dart';
```
Then access the localized string via AppLocalizations.of(context)!:
```
Text(AppLocalizations.of(context)!.helloWorld),
```

Configuring MaterialApp or CupertinoApp:

In the top-level widget (usually MaterialApp or CupertinoApp), specify language support and localization delegates:

import 'package:flutter_gen/gen_l10n/app_localizations.dart';

MaterialApp(
  // ... other settings
  localizationsDelegates: const [
    AppLocalizations.delegate, // Delegate from generated file
    GlobalMaterialLocalizations.delegate,
    GlobalWidgetsLocalizations.delegate,
    GlobalCupertinoLocalizations.delegate,
  ],
  supportedLocales: const [
    Locale('en', ''), // English
    Locale('ru', ''), // Russian
    // ... other supported languages
  ],
  // ...
);

Now the app will automatically select localization based on the user's device settings if available in supportedLocales. To manually change the locale, you can use Locale and update the app state.

How to add localization to a Flutter application?