In the latest Kojima Productions Report podcast, producer Ryan Payton announces that MGS4 won't have voice over tracks for other languages. Says Payton:
Unfortunately because of disc space, we don't have the space to include other languages, other voice over files for the respective versions. So the Japanese version's not gonna have English VO, and the North American and European versions won't have Japanese VO.
He does go on to state the voice over work in MGS4 is the best it's ever been. Kojima Pro's Aki Saito chimes in, saying they could've delayed the game to shoehorn that VO work in. But hey, the PS3 is region-free if you really, really want to hear the Japanese VO. Sounds like MGS4 is pushing the boundaries of Blu-ray space.
Session 081 [Kojima Productions Thanks, spookymulder!]