Of course i can be done, in fact it already has.
http://www.subsim.com/radioroom/showthread.php?t=134119
Alot depends on how far any modder would be prepared to go with it.
Alot of hard work world be required to model a few different subs with interiors, adding japanese voices could be done, making the crew models look oriental would even be possible, but not very easy to do with out screwing the facial animations.
The biggest problem with modeling other nations subs (besided US and German) is the lack of avliable images and research material - specifically blue prints needed for modelling accurate subs, I have never seen any pictures of IJN subs command room (on the net anyway.) Most modders dont want to pay for research material unless they have to.