Hm, yeah, it kind of crossed my mind that it could be a bit complicated whenever a language is only present in one country. The problem is where to draw the line exactly, a cursory look at the
Japanese Thread tells me that there are just as much people interested on the language (or that have Japanese ancestry, but that's besides the point) than actual Japanese people (even though Japan is pretty much the only place in the world where Japanese is actively spoken), which I guess would be one of the points this measure would try to address.
So at any rate, multi-country languages (except for English because, you know) would probably be acceptable, like, let's say for example: Spanish, Arabic, German, French, Portuguese, Tamil, Bengali, and Russian (maybe Chinese too, but that's a different problem altogether —hell, maybe even Dutch depending on who you're asking). And after that, I suppose we can go on a case-by-case basis: check if there are people from different places interacting with the thread, and if that's not the case, shut it down and direct them to the appropriate country's thread. I guess that, at the end of the day, it would depend on the amount of people we may get from different parts of the world. Even if the languages I listed above have lots of speakers from more than one country, it doesn't really make sense to keep a thread for it if none of the speakers visit this place.