I have a thick accent and find some words like "hippopotamus" difficult to pronounce.
What accent or dialect do you use?
My mother tongue is German. Hippopotamus is Nilferd. Sounds funny to you, yes? Like a bad name for nert?
Nilferd?  That's interesting.  What other words are tough to pronounce ?
Ah, let me think...
I read that English allows for different pronunciations and even spellings of the same word.
Very true. It is difficult. Words like "regularly" and "brewery" and "hereditary". Kind of a pattern, I think
Yes, seems like a vowel or a y after an r seems to be more difficult to pronounce.
A funny challenge from a teacher: try to say "red lorry, yellow lorry" many times fast. VERY hard for me!
Ah, that's name of a British punk band from 1981.