Here are some tips for internationalising the guvnor GUI.
We are always keen on volunteers who can contribute translations, either new ones or to exisiting partially finished ones.
Guvnor uses resource bundles (which is pretty standard for java). There is Constants.properties - which is the default language. You can find that in
If you add Constants_pt_BR.properties then that would contain translations for Brasilian Portugese etc etc...
At runtime, the app selects the locale based on URL (putting locale=pt_BR at the end of the URL), the locale of the browser or a meta tag in the HTML page.
In code, the Constants.java interface is used, as per GWT static string Internationalization.
Many IDEs have editors that allow you to edit resource bundles, and there are no doubt many other tools.
If you are interested in voluntering, contact michael DOT neale at gmail.