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§Externalising messages and internationalization

§Specifying languages supported by your application

You specify languages for your application using language tags, specially formatted strings that identify a specific language. Language tags can specify simple languages, such as “en” for English, a specific regional dialect of a language (such as “en-AU” for English as used in Australia), a language and a script (such as “az-Latn” for Azerbaijani written in Latin script), or a combination of several of these (such as “zh-cmn-Hans-CN” for Chinese, Mandarin, Simplified script, as used in China).

To start you need to specify the languages supported by your application in the conf/application.conf file:

play.i18n.langs = [ "en", "en-US", "fr" ]

These language tags will be validated used to create Lang instances. To access the languages supported by your application, you can inject a Langs instance into your component.

§Externalizing messages

You can externalize messages in the conf/messages.xxx files.

The default conf/messages file matches all languages. You can specify additional language messages files, such as conf/messages.fr or conf/messages.en-US.

You can retrieve messages for the current language using the play.i18n.Messages object:

String message = Messages.get("home.title");

The current language is found by looking at the lang field in the current Context. If there’s no current Context then the default language is used. The Context’s lang value is determined by:

  1. Seeing if the Context’s lang field has been set explicitly.
  2. Looking for a PLAY_LANG cookie in the request.
  3. Looking at the Accept-Language headers of the request.
  4. Using the application’s default language.

You can change the Context’s lang field by calling changeLang or setTransientLang. The changeLang method will change the field and also set a PLAY_LANG cookie for future requests. The setTransientLang will set the field for the current request, but doesn’t set a cookie. See below for example usage.

If you don’t want to use the current language you can specify a message’s language explicitly:

String title = Messages.get(Lang.forCode("fr"), "hello");

§Use in templates

You can use the Messages.get method from within a template. This will localize a message with the current language.

@import play.i18n._
@Messages.get("hello")

You can also use the Scala Messages object from within templates. The Scala Messages object has a shorter form that’s equivalent to Messages.get which many people find useful. If you use the Scala Messages object remember not to import the Java play.i18n.Messages class or they will conflict!

@Messages("hello")

Localized templates that use Messages.get or the Scala Messages object are invoked like normal:

public Result index() {
    return ok(hellotemplate.render()); // "hello"
}

If you want to change the language for the template you can call changeLang on the current Context. This will change the language for the current request, and set the language into a cookie so that the language is changed for future requests:

public Result index() {
    ctx().changeLang("fr");
    return ok(hellotemplate.render()); // "bonjour"
}

If you just want to change the language, but only for the current request and not for future requests, call setTransientLang:

public Result index() {
    ctx().setTransientLang("en-US");
    return ok(hellotemplate.render()); // "howdy"
}

§Formatting messages

Messages are formatted using the java.text.MessageFormat library. For example, if you have defined a message like this:

files.summary=The disk {1} contains {0} file(s).

You can then specify parameters as:

Messages.get("files.summary", d.files.length, d.name)

§Notes on apostrophes

Since Messages uses java.text.MessageFormat, please be aware that single quotes are used as a meta-character for escaping parameter substitutions.

For example, if you have the following messages defined:

info.error=You aren''t logged in!
example.formatting=When using MessageFormat, '''{0}''' is replaced with the first parameter.

you should expect the following results:

String errorMessage = Messages.get("info.error");
Boolean areEqual = errorMessage.equals("You aren't logged in!");
String errorMessage = Messages.get("example.formatting");
Boolean areEqual = errorMessage.equals("When using MessageFormat, '{0}' is replaced with the first parameter.");

§Retrieving supported languages from an HTTP request

You can retrieve a specific HTTP request’s supported languages:

public static Result index() {
  return ok(request().acceptLanguages());
}

Next: Dependency Injection

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