We've seen the same problem with some of our promoted posts and we get a lot of foreign language comments on our posts that sound really spammy. One clue is we

We've seen the same problem with some of our promoted posts and we get a lot of foreign language comments on our posts that sound really spammy. One clue is we usually get a message from someone who say's "we sent 5 likes to your post, please like our page back" or something to that effect. I'm guessing these are "like" harvesters who hope that spamming other people's posts with likes, they will in return get some likes back to their client's posts.