Different English accents have a massive variety of vowel and consonant sounds, and usually one can find a "difficult" vowel sound in some English accent. As a counter-example, in my experience Spanish accents have very little vowel sound variation.

Perhaps learning how to mimic accents of people from different regions (Irish, Jordie, Scottish, Alabama, BBC etc etc) of your own mother tongue gives you opportunity to learn how to hear and say different vowels and consonants from another language. Or practice the accent off non-native speakers e.g. a French accent for a Parisian speaking English.