I completely understand! I'm also Polish American. I have to say it helps when mother's side of family is Gdańsk+west and father's Lublin+east. My wife's family is all from Warsaw area and I had to translate for my father-in-law during a holiday to Władysławowo-Hel (probably helps my aunt's father's side is Kashubian too, mmm... dessert first).

I was blown-away on holiday to Croatia. It was so unexpectedly relatively easily understandable after Czechia, Austria, and Slovenia. I was all, "What just happened!? Shouldn't this be something more like Italian?"

It took only a month for me to be able to communicate in Ukrainian with my ESL students, you're totally right about Cyrillic. And I too think in concepts but switch my brain to express them externally via language, whatever that language may be at the moment. I am terrible at translating OTOH, so unnatural!

But it has it's limits, I got to a point after German and Norwegian that I thought I harbored a super-power. Then I went to school in Hungary ;) I also had an ESL student from Lithuania, yep incomprehensible.