Final Fantasy XIII is a multiplatform title. Everywhere except Japan, that is, where the game's development staff insisted in past interviews that a domestic 360 release was out of the question.
It looks like Square Enix has done some rethinking. This week's Dengeki PlayStation appears to have confirmation of a 360 release. The magazine does not hit until later this week, but details, along with some convincing images, have leaked out in advance.
According to the leaks, the 360 release is set for December 16 -- just about the one year anniversary of the PS3 version's December 17, 2009 release. Xbox 360 owners will get English voice acting and a new easy mode. As a first print run bonus, Square Enix is readying a booklet with a visual art collection, a collection of unseen event scenes, and a novel (presumably the Episode Zero Promise prologue).
The magazine does not list a price. Nor does it say if Japanese voices will be included as well. It's not uncommon for Square Enix to release "international" versions of their games featuring English voice acting in place of the original Japanese voices, although the platform usually stays the same for these.
So why is this news appearing in a PlayStation exclusive magazine? It's not uncommon for Dengeki PS to print news bits about other platforms, especially when it concerns traditionally PlayStation series. This Final Fantasy XIII news appears to be just a small blurb in the magazine's news section.
Microsoft is scheduled to have one of its seasonal press conferences later this week. Assuming the leaked images are accurate (and they do look pretty legit) this will likely be the event's big announcement."
TLDR: It's basically a Japanese release of FFXIII for the Xbox360 with a few added trinkets (equivalent to pre-order bonuses) and an "Easy mode"
However, there hasn't been official info coming from square so there could be more to this FFXIII international edition thing