I have had
Silent Hunter Mods Forum as a multi-language forum since the very beginning, but it does not accumulate much more native language forum members being active in their own languages anyway. And I seriously doubt it will be any better in Subsim. Subsim is still regarded as an anglophone forum, and the German native speaking members and guests will most likely frequent the German Ubi forum and MarineSims.de the most as they have always done.
Then again, it can't hurt...