Well, i think it's Chinese language that's most difficult to learn. Since i prefer using listen and speak method to learn a language, it's always been a nightmare to pronounce chinese words, i don't even mention chinese letters, i don't get it, how do they understand a bunch of crazy sticks dancing on the paper :D
Now I think Arabic, Because of I have a little concept of Russian.
Andres Thank you for comment))I can help you with Russian, I need to study English)
I believe the hardest to learn are languages that have a little in common with your native language. For me, semitic languages and chinese seem to be very hard to learn. On the other hand, I suppose that with a right attitude everything is possible. Referring to russian, I've never learnt it on any course, only my mum has recently taught me the alphabet, so now I am able to understand some texts thanks to the similarity to polish. I hope I master russian fluently one day.
i would like learning to speak russian but it's so difficult to me.. maybe at the start all new languages are not so easy but when we excersize i think every problem diseppear...
have a nice day