I’ve taught UX design, so I can see what you’re trying to do 
Unfortunately, on this topic my imagination as a user is too limited to produce anything vaguely credible. If I resort to magic though, I can perhaps try something.
Imagine a magic technology that translates texts from any language to any language. Then, my ideal solution would be a unified forum with a set of meaningful categories and tags that I would choose according to my interests, including some for world regions. And all messages would be presented to me in my native language.
Alternatively, comparing to my experiences as a computer programmer, another ‘ideal’ world would be one where everybody speaks English. Once again, a unified forum with categories for world regions but the forum would be 100% in English.
In the real world now… let’s see if clever ideas emerge. I liked the idea of one server per language because it would be easy to select your favorite languages (just connect to the corresponding servers) , but I’m sure there are various drawbacks to that. And it probably does not help much with local tag-cultures.