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The PersistentLocale service can be used to programmatically override the locale for the current request. Note: You should be careful to only set the persistent locale to a supported locale.

@Inject 
private PersistentLocale persistentLocale;

void onActionFromLocaleToggle() {
    if ("en".equalsIgnoreCase(persistentLocale.get().getLanguage())) {
        persistentLocale.set(new Locale("de"));
    } else {
        persistentLocale.set(new Locale("en"));
    }
    return this;
}
public String getDisplayLanguage() {
    return persistentLocale.get().getDisplayLanguage();
}

Once a persistent locale is set, you will see the locale name as the first virtual folder in page render and component event requests URLs. In this way, a persistent locale will, in fact, persist from request to request, or in a user's bookmarks.

You should be careful to only set the persistent locale to a supported locale.You will see the new locale take effect on the next request. If it is changed in a component event request (which is typical), the new locale will be used in the subsequent page render request.

Note that the locale for a page is fixed (it can't change once the page instance is created). In addition, a page may only be attached to a request once. In other words, if code in your page changes the persistent locale, you won't see a change to the page's locale (or localized messages) in that request.

Built-in Locales

While your application can support any locale (and thus any language) that you want, Tapestry provides only a limited set of translations for its own built-in messages. As of Tapestry 5.3, the following locales have translations provided:

Providing translations for Tapestry built-in messages

Fortunately, Tapestry uses all the same mechanisms for its own locale support as it provides for your application. So, to support other locales, just translate the built-in message catalog (property) files yourself:

<style type="text/css">table.sectionMacro { width: auto; }</style>

To have Tapestry use these new files, just put them in the corresponding package-named directory within your own app (for example, src/main/resources/org/apache/tapestry5/core.properties).

Finally, please open a new feature request here and attach the translated files so that they can be included in the next release of Tapestry.