Christoph, the instructions at the beginning of this thread will get you 2/3 of the way to a bilingual PP (although I would also be interested in how phoetic.de pulled it off). I am waiting to get the 1.5 Final before transferring all my language hacks to the index.php file.
My wife's site is an example of the script above:
http://photoblog.sophiepasquet.com
Rob