Less flippantly, a subject you never hear about in the United States is linguistic registers. These are effectively different modes of speech which may have different vocabularies, different grammar and - most importantly - different users.
English, so far as I know, has one register. That means that Americans are expected to know all of that shit without any acknowledgement that a lot of it is specific use. On the other hand, Thai (for example) has five registers and not everyone can write, speak, read or even understand all of them.
German has three genders. Spanish has two. English has one. The lack of inflections in English increases the vocabulary and the complexity of its use. etc. etc. etc.