operation mosun - what exactly does it entail?

[Sailor Steve]

That's because you're reading and posting in the main Pacific SH4 forum. There is a forum just for the U-boat side of SH4.
http://www.subsim.com/radioroom/forumdisplay.php?f=234

Operation Monsun was a one-man operation, so there are going to be details lacking, but it is a total fleshing out of the U-boat side of the game. The AI is good, the gameplay is good, and most who give it a chance end up liking it. What it lacks that mods like GWX have is in the details: The fully fleshed-out harbors and the little things like American convoys escorted by blimps. There are a couple of unresolved issues such as proper crew numbers, especially in the Type II. If you can live with those the game is well worth your time. And Traveller is developing a new mod that addresses many of those issues.

And yes, separate installs using MultiSH4 is the way to go, as SH4 doesn't support separate languages as SH3 does.

I hope this answers your questions.