Shortly after BlizzCon 2015, Square Enix announced to distribute localized version of Overwatch in Japan in spring 2016. However, Square Enix will only bring the game to PS4 platform, which means players of other platforms won't be able to play localized Japanese version. On the other hand, the Japanese official site has been live.
You can watch the Overwatch Japanese version trailer below with Japanese voice acting.
The version Square Enix to release in Japan is Overwatch: Origins Edition, which includes 5 heroes skins. The game will be available to purchase at 7800 yen, roughly $63 USD (Blizzard's Origins Editions is priced at $60 USD).