If you're gonna make your characters Polish-Americans...

The point you make is valid, however that's not how language works. When the tongue of the old country filters down into American (or whatever) society, there are changes made to the language. Right at the start of the movie, Stef says "Pam made pierogies", when as a Polish-American he should know that 'pierogi' is already plural.

The same thing happened in The Sopranos. Words mispronounced from the original southern Italian dialect, malapropisms abounded, words used oddly, left right and centre.

Quand le doigt montre le ciel, l'imbécile regarde le doigt.

Whenever I speak Spanish (I was born in the US to parents who moved to the states as adults) I get told by friends and relatives that have never lived in the states to learn how to speak and pronounce the language properly or to not attempt to speak Spanish.

And then I've got people upset of my Spanglish. I'm sure there are people upset over how every language changes once it is introduced in a different country with a different language.

I wouldn't have known if I didn't read this, but now I'm thinking that maybe he mispronounced the word on purpose. Maybe Pam's gowumpki is rather lump-ki! Obviosly Roman wasn't interested in eating any of it, as he told Henry to "go get some food", which while watching, I took to mean "real food".