Actually, come to think of it, in English I will sometimes say “pierogis” as well for the plural. My father has the habit of double-pluralizing when he borrows English words and puts them into Polish, so a phrase like hot dogs becomes hot dogsy in Polish-English. (The proper Polish plural would be hot dogi for the borrowed word.) He’s the only one I know who seems to do it this way.
Trying to preserve plural forms from another language is a fool’s errand.
Take paparazzi. That’s an Italian plural. The singular is paparazzo (male) and paparazza (female). Egad, like we need more gender specific job descriptions now.
Just going with paparazzi as singular and plural works, but I would have no problem with paparazzis.