The way I see it, every language have its quirks, and I think it's because of many years of that language evolving in which some stuff got added that make some weird exception at first glance (The Goose/Geese and Moose/Moose words come to mind)

With Spanish, I think the hardest thing to learn could be the allocation of the diaeresis (the ´ sign above the vocal), because you need to know if the word is having the strong pronunciation in the last or penultimate syllable and checking if the word ends with either an "n", "s" or a vowel. I never knew why, and yet somehow it just became second nature to me.

Lastly, here's a comedy sketch about the japanese language:

This will make a nice reaction image.