If Polish people annoy you by speaking in General, put them on IGNORE. Nothing you can do about it, it's up the the mods to re-enforce the rules, not you, whether they are there or not. As others said, screen-shotting and whisking it off to a moderator is the only way. And really, I doubt they can understand you. If you really want them to stop, go to Google translate and send them a whisper in their own language asking politely for them to withdraw.