What is the most difficult non-English tongue twister you know?

A couple from Modern Greek:

• Μια πάπια μα ποια πάπια. mja papja ma pja papja. “A duck, but which duck?” Surprisingly difficult.
• Άσπρη πέτρα ξέξασπρη κι απ’ τον ήλιο ξεξασπρότερη. aspri petra kseksaspri c ap ton iʎo kseksasproteri. “White stone, utterly white, even more utterly white than the sun.”
• Ο παπάς ο παχύς έφαγε παχιά φακή. Γιατί παπά παχύ έφαγες παχιά φακή; o papas o paçis efaʝe paça faci. ʝati papa paçi efaʝes paça faci? “The fat priest ate thick lentil soup. Why, fat priest, did you eat thick lentil soup?”