WBA Interactive is planning to release Metal Slug XX in South Korea on December 11th. That's twelve days earlier than the Japanese release date of December 23rd.
Maybe it's a logistics issue, considering how half of pre-orders in Japan are supposed to come with
prisoners' underpants. WBA Interactive isn't going with this promotion, so that could be a reason. Or it could be the fact that WBA Interactive wants to take advantage of the holiday season and get as many copies sold by Christmas.
Unfortunately for the rest of us, there is absolutely no mention of further releases anywhere else. There is no announced plan of release in other parts of Asia, Europe and Americas; SNK Playmore's Hong Kong-based distributer and Ignition Entertainment are very silent about the upcoming release. Well, that's nothing to be very surprised about considering the misfortunes surrounding the original Metal Slug 7 for Nintendo DS, which had its ROM dumped more than a full week before the actual release date, as well as mediocre sales. Thankfully, PSP isn't region locked, so as long as you don't mind paying for ludicrious shipping fees to get the game imported, there won't be many problems trying to play the game, provided that you can navigate through the game's UI in Japanese.