So, Carmelita isn’t Spanish
Or not explicitly Spanish, rather.
Just checked the wiki; there’s nothing in any of the games pinning her to any country in particular, and googling “Carmelita Fox nationality” just reveals a fanwiki discussion to that effect. The two frontrunners are Spain and Mexico, but there’s nothing solid enough to break the tie between them.
Personally, I always subconsciously assumed Spanish. Guess it’s in headcanon territory, for the moment at least.