Yes, "Appeler un chat un chat" doesn't actually makes that much sense when translated literally, but that's usually the case with idioms. You get an idea of what it means though, as this idiom has similar versions in other languages, as well (like you said "to call a spade, a spade"). All of that being said, "Appeler un chat un chat" means to say everything as it is or to be direct. As for the English version "to call a spade, a spade", I have to confess that this is the first time I hear about it. Well, I actually read about it, but you get the point .