Perhaps I am also ignorant, but I thought the Latin+diacritics system was invented by a Frenchman in modern times, rather than being native to Vietnam.
At what point does something become naturalized? This feels needlessly pedantic.
What matters is that the Vietnamese use the script to write their own language, which is not the case for (say) romanized Chinese.
We had centuries of Chinese scripts, which is definitely not native, then a short lived Chinese-like writing system that is the closest thing to "native", (it's not, see "Chinese-like"). Even that was not used as official system for as long as the current latin alphabet.
Who said that? I certainly didn't.
It's not very nice to go around calling people ignorant, ridiculous and dumb. You should stop doing that.