You see? There you are forgetting that I read and speak French.
For “naturel” to have any chance of meaning “native,” it would have to be used as an adjective, not a noun. In the context of what Vattel is saying, “naturel” is being used as a noun.
Now, if we play your game and say that “naturel” means native, then there is no reason at all for Vattel to use indigènes in the following sentence:
Chapter XIX, § 212
“Les naturels, ou indigènes, sont ceux qui sont nes dans le pays de parents citoyens.”
Because, if we were to play your game, the above sentence would erroneously translate out as more than a little repetitive:
“The natives, or natives, are those born in the country of citizen parents.”
Hence, there is most certainly a distinction to be made between the word “naturels” and and the word “indigènes.”
In fact, if you actually read the English version of Vattel, you will notice that it DOES translate “naturel” into “natural-born,” but flips the word order:
http://www.constitution.org/vattel/vattel_01.htm
Chapter XIX, § 212:
“The natives, or natural-born citizens, are those born in the country, of parents who are citizens...”
So, what is it? Is “naturels” native? Or, is it more accurately translated to natural-born? If it is “native,” then when did “indigènes” become a better replacement for “natural-born” when translating?
Your whole thesis relies on a mistranslation of the title for Chapter XIX, § 212, but that does nothing to change the meaning of the actual text contained within that section, which still translates out (insert either word here) to “natural-born.”
Cheers