I'm hungarian, and since we share many vowels, I never struggled with those. We even have something similar to the ch shound so that wasn't that difficult either. One word I still can't pronounce properly however is Euro. It has that throat sound that I just cant get the hang of.

interesting for me hearing and saying the german u and ue has been easy. how ever id say took me about 6 months to hear the difference in the oe sound. im 9 months in learning the language and that sound still scares me