a Polish speaker who typically cannot say the gliding dipthong of the English word
of course they can, Polish has glides, but most intro textbooks don't describe English vowels very well so they get frozen bad pronunciations. They probably find it awkward to produce so many glides but that's a separate issue.
Also Polish speakers have problems with are reducing vowels to almost nothing.
I've never understood the problems many have with ship and sheep (for instance). One reason might be that most textbooks described vowels as long and short (which kind of works in British pronunciation) and not tense and lax (what American pronunciation is based on).
ship has a lax vowel and sheep has a tense vowel but Polish doens't do tense lax distinctions wtih vowels (though it plays a part with consonants as soft consonants tend to be more lax than hard ones.