By default the voiceovers in Persona 5 will be in English. However, with some DLC you can change that.
To enable the Japanese voiceovers, simply head to the PlayStation Store and look for the Persona 5 page. From there, press down until you get to the Add-Ons area, and locate "Japanese Audio Track". Upon downloading and installing this head into the game.
You can enable the Japanese Audio Track DLC from the New Game menu.
Note that this DLC is free and accessible to all owners of Persona 5. However, it is a 2.9GB download.
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The sequel to the award winning Hellblade: Senua’s Sacrifice, Senua returns in a brutal journey of survival through the myth and torment of Viking Iceland. Intent on saving those who have fallen victim to the horrors of tyranny, Senua faces a battle of overcoming the darkness within and without.