Hi Christian,
I would suggest you to install dotLRN so you can see how it works, as long as I know every package that uses dotLRN is ready for internationalization, you will find the "change locale" link that you are looking for.
The server effort for translating is at http://translate.dotlrn.collaboraid.net/
I have done i18n stuff with the survey module, Dave has now it, I don't know if anyone else have done something else with other packages.
