There are dangers of people using that language as a loophole to spread misinformation, hate, or any type of normally restricted content. If Facebook does not have the ability to properly regulate posts that are written in a language unknown to moderators, then the people who's first language is that are at risk for negative influences.

I read this article which talked about how Tumblr went from a very large sharing platform to its now more dead site. Tumblr grew in popularity with creative users and fandoms, but once Yahoo bought the site it began to die out. This was due to aggressive moderation and then a later ban on adult content which steered many off the site.