Hard nut to crack

ʔɡvz kʃʔ lfitsvχ iː dʒiː əʊ zɛd keɪ eɪ ɛs eɪtʃ iː ɛl iː ɛf aɪ tiː zɛd juː eɪ siː eɪtʃ

In Hebrew אגוז קשה לפיצוח (egoz kashe lefitzuach)

This idiom is used in Hebrew.