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https://github.com/dart-archive/intl

Internationalization and localization support
https://github.com/dart-archive/intl

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Internationalization and localization support

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README 

        
## This repository has been moved to https://github.com/dart-lang/i18n/tree/main/pkgs/intl. Please file any PRs and issues there.

---



[![Dart CI](https://github.com/dart-lang/intl/actions/workflows/test-package.yml/badge.svg)](https://github.com/dart-lang/intl/actions/workflows/test-package.yml)

[![Pub](https://img.shields.io/pub/v/intl.svg)](https://pub.dev/packages/intl)



Provides internationalization and localization facilities,

including message translation, plurals and genders, date/number formatting

and parsing, and bidirectional text.



## General

The most important library is [intl][intl_lib]. It defines the [Intl][Intl]

class, with the default locale and methods for accessing most of the

internationalization mechanisms. This library also defines the

[DateFormat][DateFormat], [NumberFormat][NumberFormat], and

[BidiFormatter][BidiFormatter] classes.



## Current locale



The package has a single current locale, called [defaultLocale][defaultLocale].

Operations will use that locale unless told to do otherwise.



You can explicitly set the global locale



```dart

Intl.defaultLocale = 'pt_BR';

```



or get it from the browser



```dart

import 'package:intl/intl_browser.dart';

...

findSystemLocale().then(runTheRestOfMyProgram);

```



To override the current locale for a particular operation, pass the operation

to [withLocale][withLocale]. Note that this includes async tasks

spawned from that operation, and that the argument to

[withLocale][withLocale]

will supercede the [defaultLocale][defaultLocale] while the operation

is active. If you are using different locales within an application,

the [withLocale][withLocale] operation may be preferable to setting

[defaultLocale][defaultLocale].



```dart

Intl.withLocale('fr', () => print(myLocalizedMessage()));

```



To specify the locale for an operation you can create a format object in

a specific locale, pass in the locale as a parameter to methods, or

set the default locale.



```dart

var format = DateFormat.yMd('ar');

var dateString = format.format(DateTime.now());

```



or



```dart

print(myMessage(dateString, locale: 'ar');

```



or



```dart

Intl.defaultLocale = 'es';

DateFormat.jm().format(DateTime.now());

```



## Initialization



All the different types of locale data require an async initialization step

to make

sure the data is available. This reduces the size of the application by only

loading the

data that is actually required.



Each different area of internationalization (messages, dates, numbers) requires

a separate initialization process. That way, if the application only needs to

format dates, it doesn't need to take the time or space to load up messages,

numbers, or other things it may not need.



With messages, there is also a need to import a file that won't exist until

the code generation step has been run. This can be awkward, but can be worked

around by creating a stub `messages_all.dart` file, running an empty translation

step, or commenting out the import until translations are available.

See "Extracting and Using Translated Messages"



## Messages



Messages to be localized are written as functions that return the result of

an [Intl.message][Intl.message] call.



```dart

String continueMessage() => Intl.message(

    'Hit any key to continue',

    name: 'continueMessage',

    args: [],

    desc: 'Explains that we will not proceed further until '

        'the user presses a key');

print(continueMessage());

```



This provides, in addition to the basic message string, a name, a description

for translators, the arguments used in the message, and examples. The `name` and

`args` parameters must match the name (or ClassName_methodName) and arguments

list of the function respectively. For messages without parameters, both of

these can be omitted.



A function with an Intl.message call can be run in the program before any

translation has been done, and will just return the message string. It can also

be extracted to a file and then be made to return a translated version without

modifying the original program. See "Extracting Messages" below for more

details.



The purpose of wrapping the message in a function is to allow it to

have parameters which can be used in the result. The message string is

allowed to use a restricted form of Dart string interpolation, where

only the function's parameters can be used, and only in simple

expressions. Local variables cannot be used, and neither can

expressions with curly braces. Only the message string can have

interpolation. The name, desc, args, and examples must be literals and

not contain interpolations. Only the args parameter can refer to

variables, and it should list exactly the function parameters. If you

are passing numbers or dates and you want them formatted, you must do

the formatting outside the function and pass the formatted string into

the message.



```dart

greetingMessage(name) => Intl.message(

    'Hello $name!',

    name: 'greetingMessage',

    args: [name],

    desc: 'Greet the user as they first open the application',

    examples: const {'name': 'Emily'});

print(greetingMessage('Dan'));

```



There is one special class of complex expressions allowed in the

message string, for plurals and genders.



```dart

remainingEmailsMessage(int howMany, String userName) =>

  Intl.message(

    '''${Intl.plural(howMany,

        zero: 'There are no emails left for $userName.',

        one: 'There is $howMany email left for $userName.',

        other: 'There are $howMany emails left for $userName.')}''',

  name: 'remainingEmailsMessage',

  args: [howMany, userName],

  desc: 'How many emails remain after archiving.',

  examples: const {'howMany': 42, 'userName': 'Fred'});



print(remainingEmailsMessage(1, 'Fred'));

```



However, since the typical usage for a plural or gender is for it to

be at the top-level, we can also omit the [Intl.message][Intl.message] call and

provide its parameters to the [Intl.plural][Intl.plural] call instead.



```dart

remainingEmailsMessage(int howMany, String userName) =>

  Intl.plural(

    howMany,

    zero: 'There are no emails left for $userName.',

    one: 'There is $howMany email left for $userName.',

    other: 'There are $howMany emails left for $userName.',

    name: 'remainingEmailsMessage',

    args: [howMany, userName],

    desc: 'How many emails remain after archiving.',

    examples: const {'howMany': 42, 'userName': 'Fred'});

```



Similarly, there is an [Intl.gender][Intl.gender] message, and plurals

and genders can be nested.



```dart

notOnlineMessage(String userName, String userGender) =>

  Intl.gender(

    userGender,

    male: '$userName is unavailable because he is not online.',

    female: '$userName is unavailable because she is not online.',

    other: '$userName is unavailable because they are not online',

    name: 'notOnlineMessage',

    args: [userName, userGender],

    desc: 'The user is not available to hangout.',

    examples: const {{'userGender': 'male', 'userName': 'Fred'},

        {'userGender': 'female', 'userName' : 'Alice'}});

```



It's recommended to use complete sentences in the sub-messages to keep

the structure as simple as possible for the translators.



## Extracting And Using Translated Messages



When your program contains messages that need translation, these must

be extracted from the program source, sent to human translators, and the

results need to be incorporated. The code for this is in the

[Intl_translation][Intl_translation] package.



To extract messages, run the `extract_to_arb.dart` program.



```console

> pub run intl_translation:extract_to_arb --output-dir=target/directory

    my_program.dart more_of_my_program.dart

```



This will produce a file `intl_messages.arb` with the messages from

all of these programs. See [ARB][ARB].

The resulting translations can be used to generate a set of libraries

using the `generate_from_arb.dart` program.



This expects to receive a series of files, one per

locale.



```console

> pub run intl_translation:generate_from_arb --generated_file_prefix=

     

```



This will generate Dart libraries, one per locale, which contain the

translated versions. Your Dart libraries can import the primary file,

named `messages_all.dart`, and then call the initialization

for a specific locale. Once that's done, any

[Intl.message][Intl.message] calls made in the context of that locale

will automatically print the translated version instead of the

original.



```dart

import 'my_prefix_messages_all.dart';

...

initializeMessages('dk').then(printSomeMessages);

```



Once the future returned from the initialization call returns, the

message data is available.



## Number Formatting and Parsing



To format a number, create a NumberFormat instance.



```dart

var f = NumberFormat('###.0#', 'en_US');

print(f.format(12.345));

  ==> 12.35

```



The locale parameter is optional. If omitted, then it will use the

current locale. The format string is as described in

[NumberFormat][NumberFormat]



It's also possible to access the number symbol data for the current

locale, which provides information as to the various separator

characters, patterns, and other information used for formatting, as



```dart

f.symbols

```



Current known limitations are that the currency format will only print

the name of the currency, and does not support currency symbols, and

that the scientific format does not really agree with scientific

notation. Number parsing is not yet implemented.



## Date Formatting and Parsing



To format a [DateTime][DateTime], create a [DateFormat][DateFormat]

instance. These can be created using a set of commonly used skeletons

taken from ICU/CLDR or using an explicit pattern. For details on the

supported skeletons and patterns see [DateFormat][DateFormat].



```dart

DateFormat.yMMMMEEEEd().format(aDateTime);

  ==> 'Wednesday, January 10, 2012'

DateFormat('EEEEE', 'en_US').format(aDateTime);

  ==> 'Wednesday'

DateFormat('EEEEE', 'ln').format(aDateTime);

  ==> 'mokɔlɔ mwa mísáto'

```



You can also parse dates using the same skeletons or patterns.



```dart

DateFormat.yMd('en_US').parse('1/10/2012');

DateFormat('Hms', 'en_US').parse('14:23:01');

```



Skeletons can be combined, the main use being to print a full date and

time, e.g.



```dart

DateFormat.yMEd().add_jms().format(DateTime.now());

  ==> 'Thu, 5/23/2013 10:21:47 AM'

```



Known limitations: Time zones are not yet supported. Dart

[DateTime][DateTime] objects don't have a time zone, so are either

local or UTC. Formatting and parsing Durations is not yet implemented.



Note that before doing any DateTime formatting for a particular

locale, you must load the appropriate data by calling.



```dart

import 'package:intl/date_symbol_data_local.dart';

...

initializeDateFormatting('de_DE', null).then(formatDates);

```



Once the future returned from the initialization call returns, the

formatting data is available.



There are other mechanisms for loading the date formatting data

implemented, but we expect to deprecate those in favor of having the

data in a library as in the above, and using deferred loading to only

load the portions that are needed. For the time being, this will

include all of the data, which will increase code size.



## Bidirectional Text



The class [BidiFormatter][BidiFormatter] provides utilities for

working with Bidirectional text. We can wrap the string with unicode

directional indicator characters or with an HTML span to indicate

direction. The direction can be specified with the

[RTL][BidiFormatter.RTL] and [LTR][BidiFormatter.LTR] constructors, or

detected from the text.



```dart

BidiFormatter.RTL().wrapWithUnicode('xyz');

BidiFormatter.RTL().wrapWithSpan('xyz');

```



[intl_lib]: https://pub.dev/documentation/intl/latest/intl/intl-library.html

[Intl]: https://pub.dev/documentation/intl/latest/intl/Intl-class.html

[DateFormat]: https://pub.dev/documentation/intl/latest/intl/DateFormat-class.html

[NumberFormat]: https://pub.dev/documentation/intl/latest/intl/NumberFormat-class.html

[withLocale]: https://pub.dev/documentation/intl/latest/intl/Intl/withLocale.html

[defaultLocale]: https://pub.dev/documentation/intl/latest/intl/Intl/defaultLocale.html

[Intl.message]: https://pub.dev/documentation/intl/latest/intl/Intl/message.html

[Intl_translation]: https://pub.dev/packages/intl_translation

[Intl.plural]: https://pub.dev/documentation/intl/latest/intl/Intl/plural.html

[Intl.gender]: https://pub.dev/documentation/intl/latest/intl/Intl/gender.html

[DateTime]: https://api.dart.dev/dart-core/DateTime-class.html

[BidiFormatter]: https://pub.dev/documentation/intl/latest/intl/BidiFormatter-class.html

[BidiFormatter.RTL]: https://pub.dev/documentation/intl/latest/intl/BidiFormatter/BidiFormatter.RTL.html

[BidiFormatter.LTR]: https://pub.dev/documentation/intl/latest/intl/BidiFormatter/BidiFormatter.LTR.html

[ARB]: https://github.com/google/app-resource-bundle