Currently the user when he wants German messages, has to add ?locale=de at the end of the url as in
http://localhost:7080/coregui?locale=de

There should be an automatic way to select the locale, as the browser is already sending the preferred locales.

See e.g. http://google-web-toolkit.googlecode.com/svn/javadoc/1.6/com/google/gwt/i18n/client/LocaleInfo.html#getCurrentLocale()- this seems to allow to get the wanted locale from the browser