I've said this before, but one of my favorite things that happens to media during localization is when the studio tries to pass it off as taking place in the United States when it very clearly does not. They got away with it pretty easily in the first Ace Attorney game, which just took place in \"the city\", but as the games got more involved in Japanese mythology they started digging a pretty deep hole for themselves and it was too late to say \"just kidding, we're actually in Japan\".

So sure, Nine-Tales Vale is totally inhabited by \"Japanese immigrants\", and also some thousand-year-old Japanese youkai spirits immigrated with them.