Japanese language pack

I tried uploading a ja.mo file to change my blog to Japanese, but it didn’t work very well, so I cancelled it. Perhaps the ja.mo file was not designed for the latest WP release which I am using.

Is anyone out there working on a Japanese version of WP for the latest release?

Is it possible for me to edit the currently-installed language files myself, ie., just replace English words with Japanese in a template file somewhere? There are really just a few ‘instructions’ I want to change into Japanese, not every English word on the page. To make my site more easily-navigable for the Japanese people it is designed for.