It's actually far more than just Japanese localization. It's compatibility files for the NA, AU, and EU versions to function with the newly released JP and Taiwan (TW?) versions of the game, but also includes adjustments to game code to allow for extra dump memory (enables more memory to be used on things like actor limits and higher res textures) and bug fixes for various things (apparently the augment Inflection is now fixed). A friend of mine that is vary familiar with the code recently let me know of a change in Pawn AI that now allows them to que up to 3 actions, allowing pawns to function more seamlessly by having less down-time between actions and fewer moments where they try to figure out what to do (I've tested for this and found it to be accurate).
There are likely other bug fixes, but Capcom has not said anything publicly on them outside of the few they remarked about during their twitch stream on Oct. 3rd where they answered some questions while playing Dogma. A friend that works for capcom on steam has been pestering their boss to make a full public statement about the patch notes but little has come of it (in their own words; their boss is flakey and likely busy handling SF5 and other capcom titles).