Does anyone know when it will be available in Mexico?

No one knows since it was only ever announced for the USA and Canada.

I honestly never even heard of a game having a Mexican release, usually it's just "North America" or "Worldwide". (Though looking it up, apparently El Chavo for the Wii was released exclusively in Mexico and Brazil)

Well Mexico is part of North America. So, unless they are making you change your region regardless, I would assume you should be able to play. Have you had an issue downloading it to play?