There is one thing in English that doesn't make sense to me: adding 's' (or 'es') to verbs when the subject is a third person. It seems redundant and adds no extra information to the sentence.
"I like cakes", but "he likes cakes" --> 's' serves no purpose here. In other European languages, there are conjugations for other subjects as well, e.g. in Dutch: "ik spreek", "jij spreekt", "jullie spreken". All of those conjugations are, in my opinion, purposeless in modern languages.
But as a product of linguistic evolution, they must have been there to serve a purpose. That purpose is lost now but I'm very interested in finding out what it was.