The only conceivable problem I see with native language postings is moderation. What if something that appears to be another language is really just semi-randomly generate strings? Or something offensive (or in violation of copyright laws, etc) is posted and nobody else hear speaks that language?
There are three different issues. First,
what happens if someone posts something offensive, and there's
noone here that understands the language? Let me answer
that with an old riddle If a tree falls in a forest,
and there is noone to hear it, does it make a sound?
Can something be insulting if there's noone insulted?
Does it matter?
The second issue is, what if someone posts something that's
a copyright violation. Well, what happens if someone posts
something in English that is a copyright violation? My bet
is that nothing happens, until someone notices and informs
the right people. My bet is, the same happens if someone
posts a copyright violation in a language other than English.
As for the third issue, it's far from trivial to generate
random strings that look like a language but isn't. And
suppose among the thousands of monthly posts here, one or
two are a clever spoof. I don't think that's a problem.
It hasn't been a problem in all the years this site existed,
so I wouldn't worry about it too much.