A package that supports module-level localization resource construction, which is not provided by Flutter's standard features. It provides a mechanism for large-scale Flutter projects where each package can independently manage localization resources.

Features

  • Module-independent Localization: Each package manages its own localization resources
  • Unified Language Management: Consistent language settings across the entire project
  • Automatic Code Generation: Automatic Dart code generation from ARB files
  • Mixin Provision: Localization resource sharing functionality between packages

Getting started

Describe multi-language settings in the localization section of monolith.yaml. Application and package settings can be managed separately.

# monolith.yaml
localization:
  # List of supported languages
  languages:
    - ja
    - en
  
  # Application settings
  app:
    package_name: app
    arb_path: lib/l10n/
    arb_file_prefix: intl_app_
    l10n_helper_class_name: L10nHelper
    l10n_helper_path: lib/l10n/l10n_helper.dart
  
  # Package settings
  package:
    path_prefixes:
      - app/
      - packages/
    resources_path: res/
    module_helper_class_name: L10nStringsMixin
    module_helper_path: lib/gen/strings.dart

Usage

Package Structure Example:

packages/
├── domain/
│   └── user/
│       ├── res/
│       │   └── strings.csv
│       └── lib/
│           └── gen/
│               └── strings.dart  # Auto-generated
└── screen/
    └── login/
        ├── res/
│       │   └── strings.csv
        └── lib/
            └── gen/
                └── strings.dart  # Auto-generated

CSV Resource File Example (packages/domain/user/res/strings.csv):

id,ja,en,description
user_name,ユーザー名,User Name,ユーザー名
user_email,メールアドレス,Email Address,メールアドレス
user_profile,プロフィール,Profile,プロフィール
validation_email_required,メールアドレスは必須です,Email address is required,メールアドレスの必須入力バリデーション
validation_email_invalid,有効なメールアドレスを入力してください,Please enter a valid email address,メールアドレスの形式バリデーション

Generated Dart Code Example:

// packages/domain/user/lib/gen/strings.dart
mixin L10nStringsMixin {
  String get user_name;
  String get user_email;
  String get user_profile;
  String get validation_email_required;
  String get validation_email_invalid;
}

Package Usage Example:

// packages/domain/user/lib/src/user_validator.dart
import '../gen/strings.dart';

final class _Strings with L10nStringsMixin {}

@internal
final strings = _Strings();

class UserValidator {
  String? validateEmail(String? email) {
    if (email == null || email.isEmpty) {
      return strings.validation_email_required;
    }
    
    if (!_isValidEmail(email)) {
      return strings.validation_email_invalid;
    }
    
    return null;
  }
  
  bool _isValidEmail(String email) {
    return RegExp(r'^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$').hasMatch(email);
  }
}

Application Integration Example:

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      localizationsDelegates: L10nHelper.localizationsDelegates,
      supportedLocales: L10nHelper.supportedLocales,
      // Each package's localization is automatically integrated
    );
  }
}

Additional information

This package is optimized for large-scale Flutter projects that adopt modular monolith structures.

Traditional Challenges:

  • Flutter's standard internationalization features only support application level
  • Each package cannot independently manage localization resources
  • Difficulty in separating domain logic from localization resources

Solutions by This Package:

  • Independent localization resource management per package
  • Concise resource definition based on CSV files
  • Type-safe access through automatic code generation
  • Consistent language settings across the entire project

This enables domain packages and screen packages to have their own localization resources while achieving unified multi-language support across the entire application.

Libraries

monolith_localization