I'm not sure how to use (and if i even could) such kind of input on my laptop with regular english keyboard: i've added Japanese layout with IME keyboard, but seems that even with this layout active english letters still enters in all applications. So wasn't been able to test direct input.
It's also not actually clear what does it mean "appears not to work". Does it mean that there're no letters appears in text entries at all or it's something like missed glyphs?
Can think about two possible reasons why this happens: (1) international fonts aren't enabled in user preferences (2) microsoft IME layout is like compositing input which isn't implemented yet.

Yes "microsoft IME layout is like compositing input which isn't implemented yet."

So Japanese input isn't supported. But you can do copy & paste.

It is important to support IME (TSF) for Japanese/Chinese, but I wasn't able to get around implementing it on Windows yet.

When Microsoft Japanese IME input is enabled, you select the type of character input. There is full and half width alphanumeric, hiragana (ひらがな), and full and half width katakana(カタカナ). You can use the mouse and click on the A to pull up the options. I'll try to include an attachment to show this.

It may be number 2, unless there's an international font option in blender.

Windows IME Input attachment screenshot for testing purposes - to Sergey Sharybin

True, Brian, currently you cannot type any asian characters with you local IME, and mine either.

We've discussed the same issue before. Tracker ID [#30044] https://projects.blender.org/tracker/index.php?func=detail&aid=30044&group_id=9&atid=498
See what Alexander Kuznetsov said about this.

And also there seems to be another patch http://projects.blender.org/tracker/?func=detail&atid=127&aid=30274&group_id=9 for input support such as Japanese/Chinese, etc. I hope to see its magic, as well. :)
FYI.

Cut and Paste attempt... not successful - attachment included (plane showed nothing, text shows squares)... maybe i did something wrong... look forward to when it's fixed. Thank you Alexander Kuznetsov for looking into it.

Thank you, Leon Cheung, was unaware of a prior post... will not post anything about the error again.

Cut and paste already worked. You just need to check on "Internationcal Fonts", in "User Preferences -> System", in order to display your pasted characters correctly.
if you're still puzzling about it, contact me via leon4you (.at.) gmail.com. I'll see what I can help.

Has anyone touched this issue since 2012? Latest builds still can't take IME input, and it'd be really nice to not need to copy & paste.