Hi Fenriz !
For your flags, you only need to set this link:
for your forum it would be:
where x is the languageid
So it is the same as it is now, just "langid" instead of "guestlanguageid".
Concerning the automatic language-detection: I made it

You find the hack
here ! Please be so kind and test it and give me a feedback or write a new posting in the new hack thread.
Best regards
J?rg