I would be interested to learn from your experience ;-)
What version of FrameMaker are you using? From your UTF-8 experience I guess it should be FrameMaker 8 or 9, but please tell us anyway.
To simulate a Japanese OS without having it, you could switch the "system locale" of your machine to Japanese, at lest stuff like this made FrameMaker think it was installed on a Japanese OS in earlier versions:
I'm using FrameMaker 8. I often have my system locale and language set to Japanese. Some Asian language features, such as Combined Fonts work, but the <NoLineBeginChar> function still doesn't work. So I'm stuck manually adjusting spacing to comply with Japanese line break rules...no fun!!
I know it was a long time ago... but did you find a good solution to this problem. I have a similar challenge and am currently fixing manually.
I did not, but now that you've reminded me I'm going to look at it again in FM 11. Thanks for the bump! I'll post here if I find a solution.