Swedish is hard, but like Fraggle said, I now realise a lot about how Swedes think by learning the lingo
I'd think that it was difficult. Icelandic--one of the world's most unchanged languages--is believed to be one of the hardest. Maybe Basque as well. Aside from some African languages that use clicks and such. ~String
A white South African colleague of mine speaks two clicks language; Zulu and Xhosa. It's fascinating to hear him speak them and I've probably asked so many questions about it that he hates me.