Is there any tool or script to unpack the .dat files from the Japanese version of Metal Gear Solid 4? I've searched, but it seems like only tools for the US version are available. I want to play with Japanese voice acting, but the game doesn't support Japanese audio with English subtitles. If you can also explain how to port the Japanese dub to the US version, that would be even better.

There is.

MGS4tool.7z

Hmm... The link you provided, I've already tried it, but it doesn't seem to work properly.