When I taught English in the Greek port of Piraeus, a colleague and I used to spend idle time in the staff room speculating on what the hardest language in the world might look like. Perhaps there would be different verb endings for each day of the week. Or possibly the form of address might vary according to the height of the person you were talking to.
The idea of a hardest language is, of course, nonsense. How difficult a language is depends on your starting point. As Guy Deutscher wrote in his stimulating book Through the Language Glass: “Swedish is a doddle — if you happen to be Norwegian, and so is Spanish if you are Italian.” Both Swedish and Spanish are harder for English speakers, although not nearly as hard as Arabic, which, in turn, is less difficult if your mother tongue is Hebrew, as Deutscher’s is.
But Deutscher does show that some languages have features whose complexity outstrips anything my colleague and I dreamt up. Matses, a language of the Peru-Brazil frontier, has verb forms that change depending on whether the speaker saw something with his own eyes, inferred it, relied on conjecture or heard it from someone else. Supyire, spoken in Mali, has five genders: humans, big things, small things, collectives and liquids.