For difficult languages look no further than Papua New Guinea. It has about 800+ langauges
InfoMuch to learn. All different.
And Navajo. I've heard that if you weren't born learning Navajo, you could never learn it. . . It is both tonal, logic-parsed, and has contextual grammar. One phrase could have about 200 meanings depending if you raised your voice, lowered it, dragged a vowel, whatever. Needless to say, I have no knowledge in it.