| 1 | --- |
| 2 | name: flutter-setup-localization |
| 3 | 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. |
| 4 | metadata: |
| 5 | model: models/gemini-3.1-pro-preview |
| 6 | last_modified: Tue, 21 Apr 2026 21:27:35 GMT |
| 7 | --- |
| 8 | # Internationalizing Flutter Applications |
| 9 | |
| 10 | ## Contents |
| 11 | - [Core Concepts](#core-concepts) |
| 12 | - [Setup Workflow](#setup-workflow) |
| 13 | - [Implementation Workflow](#implementation-workflow) |
| 14 | - [Advanced Formatting](#advanced-formatting) |
| 15 | - [Examples](#examples) |
| 16 | |
| 17 | ## Core Concepts |
| 18 | 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. |
| 19 | |
| 20 | ## Setup Workflow |
| 21 | |
| 22 | Copy and track this checklist when initializing internationalization in a Flutter project: |
| 23 | |
| 24 | - [ ] **Task Progress** |
| 25 | - [ ] 1. Add dependencies to `pubspec.yaml`. |
| 26 | - [ ] 2. Enable the `generate` flag. |
| 27 | - [ ] 3. Create the `l10n.yaml` configuration file. |
| 28 | - [ ] 4. Configure `MaterialApp` or `CupertinoApp`. |
| 29 | |
| 30 | ### 1. Add Dependencies |
| 31 | Add the required localization packages to the project. Execute the following commands in the terminal: |
| 32 | ```bash |
| 33 | flutter pub add flutter_localizations --sdk=flutter |
| 34 | flutter pub add intl:any |
| 35 | ``` |
| 36 | |
| 37 | Verify your `pubspec.yaml` includes the following under `dependencies`: |
| 38 | ```yaml |
| 39 | dependencies: |
| 40 | flutter: |
| 41 | sdk: flutter |
| 42 | flutter_localizations: |
| 43 | sdk: flutter |
| 44 | intl: any |
| 45 | ``` |
| 46 | |
| 47 | ### 2. Enable Code Generation |
| 48 | Open `pubspec.yaml` and enable the `generate` flag within the `flutter` section to automate localization tasks: |
| 49 | ```yaml |
| 50 | flutter: |
| 51 | generate: true |
| 52 | ``` |
| 53 | |
| 54 | ### 3. Create Configuration File |
| 55 | Create a new file named `l10n.yaml` in the root directory of the Flutter project. Define the input directory, template file, and output file: |
| 56 | ```yaml |
| 57 | arb-dir: lib/l10n |
| 58 | template-arb-file: app_en.arb |
| 59 | output-localization-file: app_localizations.dart |
| 60 | synthetic-package: true |
| 61 | ``` |
| 62 | |
| 63 | ### 4. Configure the App Entry Point |
| 64 | Import the generated localizations and the `flutter_localizations` library in your `main.dart`. Inject the delegates and supported locales into your `MaterialApp` or `CupertinoApp`. |
| 65 | |
| 66 | ```dart |
| 67 | import 'package:flutter_localizations/flutter_localizations.dart'; |
| 68 | import 'package:flutter_gen/gen_l10n/app_localizations.dart'; // Adjust path if synthetic-package is false |
| 69 | |
| 70 | // ... inside build method |
| 71 | return MaterialApp( |
| 72 | localizationsDelegates: const [ |
| 73 | AppLocalizations.delegate, |
| 74 | GlobalMaterialLocalizations.delegate, |
| 75 | GlobalWidgetsLocalizations.delegate, |
| 76 | GlobalCupertinoLocalizations.delegate, |
| 77 | ], |
| 78 | supportedLocales: const [ |
| 79 | Locale('en'), // English |
| 80 | Locale('es'), // Spanish |
| 81 | ], |
| 82 | home: const MyHomePage(), |
| 83 | ); |
| 84 | ``` |
| 85 | |
| 86 | ## Implementation Workflow |
| 87 | |
| 88 | Follow this workflow when adding or modifying localized content. |
| 89 | |
| 90 | ### 1. Define ARB Files |
| 91 | * **If creating NEW content:** Add the base string to the template file (`lib/l10n/app_en.arb`). Include a description for context. |
| 92 | * **If EDITING existing content:** Locate the key in all supported `.arb` files and update the values. |
| 93 | |
| 94 | ```json |
| 95 | { |
| 96 | "helloWorld": "Hello World!", |
| 97 | "@helloWorld": { |
| 98 | "description": "The conventional newborn programmer greeting" |
| 99 | } |
| 100 | } |
| 101 | ``` |
| 102 | |
| 103 | Create corresponding files for other locales (e.g., `app_es.arb`): |
| 104 | ```json |
| 105 | { |
| 106 | "helloWorld": "¡Hola Mundo!" |
| 107 | } |
| 108 | ``` |
| 109 | |
| 110 | ### 2. Generate Localization Classes |
| 111 | Run the following command to trigger code generation: |
| 112 | ```bash |
| 113 | flutter pub get |
| 114 | ``` |
| 115 | *Feedback Loop:* Run validator -> review terminal output for ARB syntax errors -> fix missing commas or mismatched placeholders -> re-run `flutter pub get`. |
| 116 | |
| 117 | ### 3. Consume Localized Strings |
| 118 | Access the localized strings in your widget tree using `AppLocalizations.of(context)`. Ensure the widget calling this is a descendant of `MaterialApp`. |
| 119 | |
| 120 | ```dart |
| 121 | Text(AppLocalizations.of(context)!.helloWorld) |
| 122 | ``` |
| 123 | |
| 124 | ## Advanced Formatting |
| 125 | |
| 126 | Use placeholders for dynamic data, plurals, and conditional selects. |
| 127 | |
| 128 | ### Placeholders |
| 129 | Define parameters within curly braces and specify their type in the metadata object. |
| 130 | ```json |
| 131 | "hello": "Hello {userName}", |
| 132 | "@hello": { |
| 133 | "description": "A message with a single parameter", |
| 134 | "placeholders": { |
| 135 | "userName": { |
| 136 | "type": "String", |
| 137 | "example": "Bob" |
| 138 | } |
| 139 | } |
| 140 | } |
| 141 | ``` |
| 142 | |
| 143 | ### Plurals |
| 144 | Use the `plural` syntax to handle quantity-based string variations. The `other` case is mandatory. |
| 145 | ```json |
| 146 | "nWombats": "{count, plural, =0{no wombats} =1{1 wombat} other{{count} wombats}}", |
| 147 | "@nWombats": { |
| 148 | "description": "A plural message", |
| 149 | "placeholders": { |
| 150 | "count": { |
| 151 | "type": "num", |
| 152 | "format": "compact" |
| 153 | } |
| 154 | } |
| 155 | } |
| 156 | ``` |
| 157 | |
| 158 | ### Selects |
| 159 | Use the `select` syntax for conditional strings, such as gendered text. |
| 160 | ```json |
| 161 | "pronoun": "{gender, select, male{he} female{she} other{they}}", |
| 162 | "@pronoun": { |
| 163 | "description": "A gendered message", |
| 164 | "placeholders": { |
| 165 | "gender": { |
| 166 | "type": "String" |
| 167 | } |
| 168 | } |
| 169 | } |
| 170 | ``` |
| 171 | |
| 172 | ## Examples |
| 173 | |
| 174 | ### Complete `l10n.yaml` |
| 175 | ```yaml |
| 176 | arb-dir: lib/l10n |
| 177 | template-arb-file: app_en.arb |
| 178 | output-localization-file: app_localizations.dart |
| 179 | synthetic-package: true |
| 180 | use-escaping: true |
| 181 | ``` |
| 182 | |
| 183 | ### Complete Widget Implementation |
| 184 | ```dart |
| 185 | import 'package:flutter/material.dart'; |
| 186 | import 'package:flutter_gen/gen_l10n/app_localizations.dart'; |
| 187 | |
| 188 | class GreetingWidget extends StatelessWidget { |
| 189 | final String userName; |
| 190 | final int notificationCount; |
| 191 | |
| 192 | const GreetingWidget({ |
| 193 | super.key, |
| 194 | required this.userName, |
| 195 | required this.notificationCount, |
| 196 | }); |
| 197 | |
| 198 | @override |
| 199 | Widget build(BuildContext context) { |
| 200 | final l10n = AppLocalizations.of(context)!; |
| 201 | |
| 202 | return Column( |
| 203 | children: [ |
| 204 | Text(l10n.hello(userName)), |
| 205 | Text(l10n.nWombats(notificationCount)), |
| 206 | ], |
| 207 | ); |
| 208 | } |
| 209 | } |
| 210 | ``` |