Sorry, but we have a specific example of the adjective "naturels" being translated specifically as "natural born."
Sorry, but READ the translation.
Does it read “The natural born citizen, or native?
And had native been used in two previous translations? If so, which word was translated native?
And no, you had a PHRASE, les sujets naturels, which was translated natural born subject.
Now, if THAT is what Vattel meant, he was simply wrong, since we KNOW that NBS included those born of alien parents...