If you can't understand what they are saying, then most likely they are off topic, no?
I report the posts that make completely NO SENSE whatsoever to me.
Yeah, this. I usually give them a polite warning that they should stick to their local board if they have trouble with English (you can send them a PM too if you prefer giving them some friendly advice). If they still spam in their local board then the moderator of that board should pick up on it and deal with it appropriately.