The most difficult thing is alphabet of Arabic, because it is written from right to left, and it would be changed it's shape depended on their position of words. it can make people scared to learn Arabic.

second, for Korean like me, the change of pronunciation based on speaker and listener's gender. because Korean has no similar change like this.

third, you know, Arabic language is very fragmented language not only pronunciation but also expressions of words and sentences

pronunciations and expressions are different by speaker's region and age and level of society. and I guessed usually Arabic people prefer foreigner say with similar pronunciations with theirs.

for example, "La" in Arabic is the meaning of "No". in western Arfican countries Such as Al-Magrib or Alegria or Tunisia usually said like "Le" instead of "La". in other side, Saudi Arabia or Dubai or Middle East Countries people said "LA" very strongly.

I feel that Arabic does not seem to matter much about the pronunciation of vowels. However, the pronunciation of vowels is very important in Korean, so it came as a tremendous shock.