Comprehensive Guide to Internationalization and Localization with Flutter's Intl Package

Flutter's intl package provides a robust set of tools for implementing internationalization and localization (i18n/l10n) in your Flutter applications. This allows you to support multiple languages, adapt content to different locales, and provide culturally sensitive experiences for your users.

Getting Started

1. Import the intl Package:

import 'package:intl/intl.dart';

2. Initialize the Default Locale:

By default, intl uses the system locale. To set a custom default locale:

Intl.defaultLocale = 'fr_CA';

Message Translation

1. Wrap Messages with Intl.message:

Use Intl.message to wrap messages that need to be translated. Provide a name, arguments (if any), and a description for translators.

String hiMessage() => Intl.message('Hi there!',
    name: 'hiMessage',
    args: [],
    desc: 'A friendly greeting');

2. Extract Messages for Translation:

Run extract_to_arb.dart to create an intl_messages.arb file containing all translatable messages.

$ pub run intl_translation:extract_to_arb --output-dir=target/directory my_app.dart

3. Generate Translated Libraries:

Translate the intl_messages.arb file and run generate_from_arb.dart to create localized libraries.

$ pub run intl_translation:generate_from_arb --generated_file_prefix=my_app_messages <translated_ARB_files>

4. Load Localized Messages:

Import the generated library and initialize it for the desired locale.

import 'my_app_messages_all.dart';

initializeMessages('fr').then((_) => print(hiMessage()));

Number Formatting

1. Create a NumberFormat Instance:

Specify a format string and optional locale.

var numberFormat = NumberFormat('###.0#', 'en_US');
print(numberFormat.format(12.345)); // Output: 12.35

2. Use Number Symbols:

Access the number symbol data for the current locale.

print(numberFormat.symbols.DECIMAL_SEP); // Output: '.' (decimal separator)

Date Formatting

1. Create a DateFormat Instance:

Use a skeleton or an explicit pattern to create a date formatter.

DateFormat dateFormatter = DateFormat.yMMMMEEEEd('en_US');
print(dateFormatter.format(DateTime.now())); // Output: 'Wednesday, January 10, 2012'

2. Parse Dates:

Parse a date string using the same skeleton or pattern.

DateFormat dateParser = DateFormat.yMd('en_US');
DateTime date = dateParser.parse('1/10/2012'); // Date object representing January 10, 2012

Bidirectional Text

1. Create a BidiFormatter:

Specify directionality with BidiFormatter.RTL or BidiFormatter.LTR.

BidiFormatter bidiFormatter = BidiFormatter.RTL();
String wrappedText = bidiFormatter.wrap('Hello world!');

2. Wrap Text:

Wrap the text with directional indicator characters or HTML spans.

print(bidiFormatter.wrapWithUnicode('Hello world!')); // Output: 'Hello world!'\u202C (RTL mark)
print(bidiFormatter.wrapWithSpan('Hello world!')); // Output: '<span dir="rtl">Hello world!</span>'

Conclusion

The intl package provides a powerful and comprehensive set of features for internationalization and localization. By using its capabilities, you can deliver language-aware and culturally sensitive experiences to your Flutter users.