I am looking for this answer too though I think we have to wait for the retail version to find out. I downloaded the Japanese demo and it came with Japanese text and audio, though the options displayed English (like in Vanquish) but selecting English was disabled. I would not be surprised Kojima put so many FMV's on the disc that it can only fit one language.
By the way, don't go downloading the Japanese demo unless you have a JP PS3, the demo is region locked :(
US version comes out 2.19 and JP version comes out 2.21 guess we have 2 days to decide if we should buy import :) thx for the info. but I have the product code from Z.O.E. so I can play that demo on my US PS3 ><