http://www.fgdriver.de/phpbb/index.php are the largest Large Scale only German Forum I have found yet.

Even if the name implies that most drivers are running FG's it is NOT an FG only Forum.
There is a lot of discussions going on, but 99% is in German.
(luckily I do read German :p )

People are as helpfull as I have seen here, and they are not badly plagued by Trolls.