

I took German in primary school (0.5 or 1.5 years, I forget which), Spanish and Korean in late primary school/early high school (3 years), French (5 years) and Vietnamese (1 year) in high school. Of these, I can hold a very basic conversation in French and have good enough grammar to put together fairly sophisticated sentences, very slowly, using a dictionary; and can read the Korean script (the same way someone who speaks Turkish but has literally never heard a word of the language can “read English” because their language uses the same script) and barely any more than that, in any of those languages.
I blame the fact that I changed languages so much for my poor skill in all of them. (Though a lack of will or immersion certainly has a fair amount to do with it, too.)
I do wonder if there might be a difference between the phonemes and the realisation, the way there was in German according to the German commenter.
But also, even without that, stress undoubtedly changes the perception of the vowel (not nearly as much as in English, but certainly not nil), as does an r after a vowel.