Thanks! Looks like I picked a bad test case for Polish, I tried a few more and some look perfect (boring corporate text) and others around the same as Google Translate (I don't know Polish or Spanish and mostly looked at song lyrics). I don't know if specific examples are helpful, but it looks like it particularly has a tough time with "W poprzek wpław" and I think a few more issues in:

https://www.musixmatch.com/lyrics/Teskno/Woda-t%C4%99skno-gr...

I'll add a few feature requests to the issue tracker (if not there already) hopefully later today. Including a request to put that web page in the extension :).