After a bit of digging i found the player voice files and well, since everyone loves to turn the player into their favorite anime Wafu why not go the Whole Hog and make him/her speak fluent Japanese and rely on subtitls to understand them, like a good Otaku does!
This mod replaces all the Player dialog with the Japanese version. It supports all DLC but since it just replaces audio files like for like even if you don't have the DLC the mod should work fine since theirs no actual ESP dependencies.