I don't speak Polish but I do know a few words. At the beginning of the movie, when Rush is telling about how Harvie's mother worked in the mines and got lead poisoning, remember how she drops a wheelbarrow full of something and then says something that sounds like "Kooooooorva"? I'm pretty sure that means *beep* in Polish.
Anyway, just thought I'd share. :D
That word is "kurwa" and it means "whore", but it is often used as a curse, like "Oh s h i t!"
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It is even used as something like a comma by some individuals. Some are even so extreme that it's their every second or third word.
As for the film, besides this word polish details don't seem very accurate. There is no such first name as "Harvek". "Maciek" (the father) is a diminutive form, so it wouldn't be written on his grave. "Krumpetzki" sounds possible, but it would be spelled differently, there is no "tz" in polish words.
Also, the mother doesn't speak Polish, just some gibberish. It isn't really an inaccuracy though, I can buy that as a convention.