I think the problem with the Polish language is that the stress falls on the second-last syllable, most of the times, that there are way too many feminine endings (or rhymes, whatever), way too many consonants (seriously, that "prz" thing sounds like beatboxing or awkward sneezing), way too long words etc. I think, grammatical gender also contributes to difficulty of singing in Polish. I say it as a person, who really considers singing in Polish, but finds it difficult, for some odd reason.
When I sing in English, it feels different. Vowels are in the right place, you can play with it, you can experiment with accents, you can manage to sound beautiful etc.
Anyway, that's my subjective impression.
What feels off? timing? Articulation (different for speaking and singing) breath support?