Multi-lingual support works in Tapestry as follows:
If several locales are supported by a Tapestry web application and some user visits the application for the first time, Tapestry checks for the preferred language of the user's browser (you can set the preferred language in Internet Explorer by going to Tools | Internet Options | General | Appearance | Languages, in Firefox, by going to Preferences | Advanced | General | Languages). If the web application supports the preferred language, Tapestry displays it in that language; otherwise the application is displayed in the default language.
While doing this, Tapestry applies some reasonable logic. Say, if the preferred language as set in the browser is either English (United Kingdom) or English (United States) and the supported locales are defined as "en" and "de", Tapestry will display the web application in the "en" locale.
If, while working with the application, the user switches the locale (you will see...