A special present as thanks for playing Persona 5! Download the 'Persona 5 Japanese Audio Track' to play with the original Japanese voices.
Once installed, the audio for a New Game can be set from the title screen via the Config menu. To change the audio for a game already in progress, toggle the Language option for the saved game between ENG and JPN at the Load Data menu. (Saving your progress afterward will commit your changes.) Enjoy!