I’ve been listening to some videos by a Ukrainian immigrant to Poland (he has enough Polish ancestry to be recognized as Polish and his channel is Polak z Ukrainy (A Pole from Ukraine). Mostly he compares things between the two countries like food (Polish słonina isn’t as good as Ukrainian salo while Polish wieners have much more meat content than do Ukrainian ones) and some of the things that have surprised him (Poland follows the German model where the ‘first floor’ of a building is what you’d call the ‘second floor’ in the US over the ‘ground floor’) while Ukraine follows the Russian (and US) model.
Situations that are awkward for him (described in one video) often involve speaking in public where others can hear. His Polish is very fluent but with a very heavy accent that he’s still self-conscious about (most commenters tell him he’s doing fine).
Pretty cut and dried in theory….
It does remind me of how different languages have different centers of gravity in the mouth. American English (for me) is in the middle of the mouth and requires a lot of jaw and lip and tongue movement. Polish is centered toward the front of the mouth with very little lip movement and the tongue has to be light and nimble as it alternately flattens (ś) or comes to a point (sz). Russian is all about the tongue which seems to fill the entire oral cavity and other sounds escape the mouth as best they can around this giant obstacle. But after getting past the tongue they still have to negotiate the lips (a Russophone speaking Polish seems to add a lot of English w sounds).
Russian speaking Ukrainians in Poland learn survival Polish with almost no effort but no matter how fluent they get the accent remains distinctive. I haven’t known/heard enough Ukrainians who mostly speak Ukrainian to say anything about their accents.