/flutter-setup-localization

name: flutter-setup-localization
description: Add `flutter_localizations` and `intl` dependencies, enable "generate true" in `pubspec.yaml`, and create an `l10n.yaml` configuration file. Use when initializing localization support for a new Flutter project.
metadata:
  model: models/gemini-3.1-pro-preview
  last_modified: Tue, 21 Apr 2026 21:27:35 GMT

Internationalizing Flutter Applications

Contents

• [Core Concepts](#core-concepts)
• [Setup Workflow](#setup-workflow)
• [Implementation Workflow](#implementation-workflow)
• [Advanced Formatting](#advanced-formatting)
• [Examples](#examples)

Core Concepts

Flutter handles internationalization (i18n) and localization (l10n) via the `flutter_localizations` and `intl` packages. The standard approach uses App Resource Bundle (`.arb`) files to define localized strings, which are then compiled into a generated `AppLocalizations` class for type-safe access within the widget tree.

Setup Workflow

Copy and track this checklist when initializing internationalization in a Flutter project:

• [ ] **Task Progress**
• [ ] 1. Add dependencies to `pubspec.yaml`.
• [ ] 2. Enable the `generate` flag.
• [ ] 3. Create the `l10n.yaml` configuration file.
• [ ] 4. Configure `MaterialApp` or `CupertinoApp`.

1. Add Dependencies

Add the required localization packages to the project. Execute the following commands in the terminal:

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

Verify your `pubspec.yaml` includes the following under `dependencies`:

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

2. Enable Code Generation

Open `pubspec.yaml` and enable the `generate` flag within the `flutter` section to automate localization tasks:

flutter:
  generate: true

3. Create Configuration File

Create a new file named `l10n.yaml` in the root directory of the Flutter project. Define the input directory, template file, and output file:

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

4. Configure the App Entry Point

Import the generated localizations and the `flutter_localizations` library in your `main.dart`. Inject the delegates and supported locales into your `MaterialApp` or `CupertinoApp`.

import 'package:flutter_localizations/flutter_localizations.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart'; // Adjust path if synthetic-package is false

// ... inside build method
return MaterialApp(
  localizationsDelegates: const [
    AppLocalizations.delegate,
    GlobalMaterialLocalizations.delegate,
    GlobalWidgetsLocalizations.delegate,
    GlobalCupertinoLocalizations.delegate,
  ],
  supportedLocales: const [
    Locale('en'), // English
    Locale('es'), // Spanish
  ],
  home: const MyHomePage(),
);

Implementation Workflow

Follow this workflow when adding or modifying localized content.

1. Define ARB Files

• **If creating NEW content:** Add the base string to the template file (`lib/l10n/app_en.arb`). Include a description for context.
• **If EDITING existing content:** Locate the key in all supported `.arb` files and update the values.

{
  "helloWorld": "Hello World!",
  "@helloWorld": {
    "description": "The conventional newborn programmer greeting"
  }
}

Create corresponding files for other locales (e.g., `app_es.arb`):

{
  "helloWorld": "¡Hola Mundo!"
}

2. Generate Localization Classes

Run the following command to trigger code generation:

flutter pub get

*Feedback Loop:* Run validator -> review terminal output for ARB syntax errors -> fix missing commas or mismatched placeholders -> re-run `flutter pub get`.

3. Consume Localized Strings

Access the localized strings in your widget tree using `AppLocalizations.of(context)`. Ensure the widget calling this is a descendant of `MaterialApp`.

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

Advanced Formatting

Use placeholders for dynamic data, plurals, and conditional selects.

Placeholders

Define parameters within curly braces and specify their type in the metadata object.

"hello": "Hello {userName}",
"@hello": {
  "description": "A message with a single parameter",
  "placeholders": {
    "userName": {
      "type": "String",
      "example": "Bob"
    }
  }
}

Plurals

Use the `plural` syntax to handle quantity-based string variations. The `other` case is mandatory.

"nWombats": "{count, plural, =0{no wombats} =1{1 wombat} other{{count} wombats}}",
"@nWombats": {
  "description": "A plural message",
  "placeholders": {
    "count": {
      "type": "num",
      "format": "compact"
    }
  }
}

Selects

Use the `select` syntax for conditional strings, such as gendered text.

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

Examples

Complete `l10n.yaml`

arb-dir: lib/l10n
template-arb-file: app_en.arb
output-localization-file: app_localizations.dart
synthetic-package: true
use-escaping: true

Complete Widget Implementation

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

class GreetingWidget extends StatelessWidget {
  final String userName;
  final int notificationCount;

  const GreetingWidget({
    super.key, 
    required this.userName, 
    required this.notificationCount,
  });

  @override
  Widget build(BuildContext context) {
    final l10n = AppLocalizations.of(context)!;

    return Column(
      children: [
        Text(l10n.hello(userName)),
        Text(l10n.nWombats(notificationCount)),
      ],
    );
  }
}