It's a question that's been on my mind for a while. We all know that Quebec is quite a bit different compared the rest of Canada, including even part of its provincial legal system, as well as the bilingualism, and not to mention the culture, etc.
My question is, what would it take for a Mexican Texas to end up in this same situation, that is, in which the majority speak a language that is a minority elsewhere in the country, and also has a unique culture, and even has a slightly different legal system compared to other states?
Bonus points if Mexico is a republic as per OTL.