Square Enix has not said anything official about releasing Dissidia Duodecim Prologus outside of Japan. Australia’s Classification Board says otherwise since they reviewed Dissidia Duodecim Prologus: Final Fantasy from Square Enix.
After Square Enix’s January press conference, a prologue to Dissidia 012[duodecim]: Final Fantasy was released on PlayStation Network. The game had a small storyline starring Final Fantasy XIII protagonist Lightning and an arcade mode with a small selection of playable characters. Prologus also included downloadable content to add Aerith as a support character in Dissidia 012[duodecim]: Final Fantasy.
Since its rated, perhaps Dissidia Duodecim Prologus is coming soon?