Technically Rokon and Vulpix are both correct, since in-universe they acknowledge the fact that Pokemon species have different names in different countries. Trainer names, on the other hand, don't have that going on. Unova's fourth Gym Leader is always called Kamitsure in Japanese and Elesa in English, despite the game taking place in Unova (America).
I like to think that the first four games' characters use their Japanese trainer and Pokemon names, BW/BW2 and SM use the English names, and XY has French names
