In your opinion , what is the toughest language to learn?

[unpopular]

I'll go along with what Lew said, and toss out Cherokee, maybe Inuktitut.

My mother developed the braille code for Inuktiut. She said that the structure was extremely different and was pretty challenging even as a written form.

 

[webestang6412 1]

Klingon.

I rather suspect Klingon is a fairly simple language there are many Sci-Fi buffs who seem to learn it, and there would be no point in making it complicated when designing it for TV shows.
I've even got a Christmas song 'sung' in Klingon among my MP3s

Probably so, I have a buddy who speaks Klingon all the time.