Nican Tlaca. What more can I say? When someone claims they are that, I stay silent and try my best to not laugh especially on things that are going to be said afterwards.
Someone who claims Nican tlaca might as well say "I am ignorant and can't speak Nahuatl" since it's grammatically incorrect along with native Nahuatl speakers won't understand what they're saying.
As for its origin, if looking in florentine codex or in the huejotzingo letter, it does not mean what people who push the nican tlaca term means.
There's tons of terms that Nahuas back then and contemporary nahuas use. None is nican tlaca.
It's incomplete. Nican tlaca just means person (and depending on dialect, just man) here. If people who really wanted to use as we the people here, it would be "nican titlacah" which is shown in the Florentine Codex, Annals of His Time and huejotzingo letter.
If you were to say nican tlaca to a native speaker, they will look at you hoping you'll add more to it.
Nican tlaca is grammatically correct, but it just doesn't mean what people claim it means. It means "the people here". Saying "I am nican tlaca" or "we are nican tlaca" is grammatically incorrect and meaningless from the point of view of the Nahuatl language.
What they lack is proper understanding of Nahuatl grammar. If they want to use an indigenous word to describe themselves, they should have enough respect for the language to learn the grammar.
James Lockhart, a white guy, introduced the term in his book "we people here" based on Nican Tlaca to put together a group of people as an ethnic label.
I mostly see variant of "nican tlaca" in Florentine codex with context unlike the way I see people claim it is. From Florentine Codex book 12 which is about the conquest of the Mexica by the Spaniards which isn't in the context as indigenous as a whole:
ce cioatl nican titlaca
a woman, of us us people here for literal translation or one local woman
Totomonilitztli, inic micque nica tlaca
a disease of pustules, from which the people here died or a disease of pustules from which the local people died
in iuh mochichioa nican tlaca: no iuh mochichioaia
they dressed as the people here dress or they dressed as the local people dress
Also, in the other books in the Florentine Codex, they're very specific on groups and regions when speaking of regions. I haven't seen any variant of "nican tlaca" in those other 11 books unless I missed one and you have.
A stretch on find "nican tlaca" which demonstrates it is more on context in other source is Annals of His Time: Don Domingo de San Anton Munon Chimalpahin Quauhtlehuanitzin where he wrote:
nican onehuaya mexico tlaca yc onpanahuilloya ynic ompa huia in tetzcoco
People of Mexico leaving from here were taken over by it to go as far as Tetzcoco.
Letter of Huexotzinco is only referring people of Huexotzinco and not the entire people as an identity.
Yes, an identity to unite all natives by natives in the past is nice in concept, but I haven't seen anything like "nican tlaca" in the context you guys want it to be.'
People use "nican tlacah" as if it were an english word. But Nahuatl doesn't work that way.
I'm OK with Chicanos using Nican tlaca as a label for themselves. It's when they use it by claiming it's a label nahuas (from colonial times or contemporary) used, act like it's grammatically correct or it means all indigenous people is where I have the issue.