If someone is harassing you, IMO the best approach is not blocking but contacting the admins; either of your instance or the person’s instance. If you simply block the person they’ll keep harassing you, but now on your back as you won’t see their comments.
Me, in the meantime: “fuck, now I need to know what’s written there!”, followed by machine translation, followed by a bored “…ah.”
(Replace the bored “…ah.” with some genuine laugh when it’s something from szmer.info. I don’t speak Polish but people in that instance have an odd sense of humour, that I enjoy quite a bit.)