There actually will be an NTSC-J version for the X360. December 16, 2010 is the release date.
Their first plans were not to make an X360 release for japan, but now there will be one. They announced it around TGS 2010 this september.
It will even have an "easy" mode...although the game is pretty easy as it is (auto battle option )
It's that so called "international version"
edit:
The Japanese release will be under the name Final Fantasy XIII Ultimate Hits International. "Ultimate Hits" is Square Enix's Japanese budget lineup. We're not sure just yet if this means the game will get gaudy budget packaging, but the price is being kept in check at 4,980 yen, or about half what the PlayStation 3 version originally cost at its release last year.
As for the "International" part of the name, this is being included because Square Enix is using
English voices in the game. Japanese Xbox 360 owners will have to play the game with an
English voice track.
Subtitles can be selected between
Japanese, English and various European languages.
http://xbox360.ign.com/articles/111/1118981p1.html
It will probably be region locked to NTSC-J....or not... The FF13 available now for the X360 is "PAL and NTSC-U" locked.