If they're foreigners to the language, they shouldn't be posting in it, period. The only exceptions should be heritage speakers or advanced learners, not someone with zero connection to the culture and language.
"They shouldn't be posting except in these situations where they can be posting".
Is this the true power of a 2 day old account? If there are "exceptions" then people are allowed to post.
Do you think these exceptions you mentioned are rare scenarios? Reminder that half of Europe has had its language spread throughout the world - UK to USA, Canada, Australia, Ireland - Spain to Mexico, Venezuela, etc (basically half of Latin America) - Portugal to Brazil, and several African Countries - France to a ton of African and middle east countries - Russia to most of Eastern Europe - the list goes on. The world is more connected in terms of language than you think.
Language isn't a special members club, its just how people communicate. Most people are happy and welcoming if you are learning their language as a foreigner, even if you are shit at it.
Besides, what's the problem with having people that don't speak the language post about your local Lolcows?
There are many interesting obscure people out there that deserve discussion and I really don't think this should be language gated. Drakenlord is a great example of a person of interest that we have talked about many times including on MATI, and yet he is stuck in the German board. Just this week we talked about Japanese elections and 4chan owner on Community Features and MATI.