I'm looking for a word meaning "hard to pronounce"

I believe the word you are looking for is mouthful.

Dictionary.com defines mouthful as (amongst other meanings) :

A long word or group of words, especially one that is hard to pronounce.

It is commonly used in English - e.g., "that was a real mouthful."

A word difficult to pronounce is "a jawbreaker"

• jawbreaker - "a word that is difficult to pronounce" - TFD

"a tongue-twister" usually refers to a word or sequence of words difficult to pronounce.

• tongue-twister - "a word or sequence of words difficult to pronounce, especially rapidly, because of alliteration or a slight variation of consonant sounds" - DC

examples of jawbreakers (for some people)

• "supercalifragilisticexpialidocious"
• "diaphragmatic"
• "fait accompli"
• "dowager"

examples of tongue-twisters:

• "where she sits she shines, and where she shines she sits."
• "can you can a can as a canner can can a can?"
• "I wish I were what I was when I wished I were what I am.