I read somewhere, in passing that, the Castilians were very strict in insisting that they were in control of the various American possessions and colonies from day one, at the expense of the other constituent members or language groups. Apparently this was as much from the organs of central government as it was from commercial or other interests. I guess it was also part of a wider Castilianisation process that went on for many centuries.
Anyway, is it at all possible with an POD (maybe early? Around the time of the two Catholic Monarchs perhaps) to at least allow one of the other language groups to establish a meaningful settlement with their own language group?
The obvious parties would be the Aragonese & Catalans, as the other party to the union of crowns, but also to the Basque, Galacians and other less known language groups.