It also doesn't help when words in a single language that can refer to the same thing have different grammatical genders (e.g. месяц vs луна).

For extra spiciness, try the same word in all three genders, with different meanings in each one:

DE:

der Band ... volume (as in "the second volume in a collection of books")

die Band ... group (as in "the Beatles are a group")

das Band ... ribbon

To nobody's surprise ніж, світ, жаба have exactly right genders so it's Germans who are confused.

But, for some weird reason, modern Bulgarian mutated gender of "evening" to feminine:

Тази вечер

even though in the greeting "good evening", the old masculine form remains:

добър вечер

Bulgarian in general seems to be the Chad of the Slavic language family :)