The most difficult language to learn

[Discuss]
What is the most difficult language to learn?
for a native English speaker... I think it's Chinese :(

percieved "learning difficulty" by adults is irrelevant, jap is reputed to be hard but it was a breeze for me as I speak an azn trash language myself.

A real measure of these could be a comparison of how late kids gather decent speech capabilities. I heard Arabic failed in that, but it could be something related to writing and not speaking too, I can't remember for sure now.