Theyd have to either learn about another culture, they already know the US and Japan pretty well and can largely extrapolate for others.  It could be pretty cool and I'd be interested in seeing more games set in fictional or real world South American countries, but America/Japan is a pretty easy target and Generic Euro country isnt much harder.  Give them funny hats, an accent, and a misplaced sense of superiority and you're done.

I think there's also sort of an issue of recognizability.

Everyone knows America.  Everyone knows Japan.  Everyone knows England.  Spain and France and maybe like Ireland/Scotland/Place Where Folks Wear Kilts and Drink Beer, they're fairly well known.  Brazil isn't widely known enough for anything kid friendly enough for a Pokemon game.  Maybe I'm just ignorant but I don't think a lot of South American countries are.

Maybe Pokemon Cuba.  That could actually be really cool.  Actually I'd be down for a game set in Brazil too.  They'd likely lean heavily on Carnival, but if they put some effort into it it could be pretty cool and maybe it could teach folks something about Brazil.