This is like with me and my little brother, we always fight of ho has the reason.Oh well. In fact mine L1 is Polish, but that doesn't means I have to post in Polish. Try to understand that making many local-oriented subforums will split discussion between them, making then unreadable for others. The way we develop TMW determine that we have to understand each other. So the best solution in this case is to create own forum in Spanish, German, Polish, etc. If need this for some reasons I think It wouldn't be a problem to provide link to forum on main TWM site.
And of course there is another reason why we don't implement multi-lingual forums. That reason is limited bandwidth. As you noticed TMW is non commercial project. We can not afford to pay for super-hiper-extra-turbo hosting which will handle such traffic.
My answer for multi-lingual support on forums is NO.
But let see i have no knowledges of create forums, and even if i do it, i could not maintenance it.
And i put it in English and Spanish, for that everybody understand that the two things are the same.
FOR YOU ITS NO AND FOR ME ITS YES, ITS DISCUSSION; JUST THAT.
PS: Its TMW not TWM. Of course, a mistake is a mistake.