do not count legally as substitutes for the authentic version isn't the exact same wording, but I don't think it's a leap to go from "this is not a legal document" to "this is not to be used in court" when referring specifically to contracts and licenses.
It's at least no more of a leap than telling someone they're lying when they're paraphrasing, and in a way many people think is fairly accurate.
You're being oddly pedantic. The translations aren't authorized by the FSF to be used as the translation of their licenses i.e. they entirely reserve the right to dispute the text of any of them.
You can use an empty soda can in court. The FSF probably hopes that they are used in court as a starting point.
It's at least no more of a leap than telling someone they're lying when they're paraphrasing, and in a way many people think is fairly accurate.