I am no expert and I hesitate to reply because you are looking to spend
money on something and I fear I could wrongly advise. I suspect, however,
that there a few experts in this area here so I'll offer my two penn'orth.
This is exactly the kind of thing that can catch you by surprise but there
shouldn't, in theory, be any issues. There are Japanese language features
that may not be available in an English version by default but if you enable
Japanese language support they should then become available.
However, the way language support works in 2007 is a little different from
the way it works in 2003 and you may find, on a Japanese version of Windows,
that you see some odd effects. For example there are interactions between
the (Windows) keyboard settings and Word's langauge settings. I am guessing
a bit here - I don't speak any Japanese - because I have seen strange
language effects (nothing critical - things in the wrong language, things
displayed in one language but sorted as though displayed in another, etc.)
when mixing European languages and they don't have all the complication of
text direction issues.
I believe that all versions of Office come with English (please confirm this
before relying on it) so you should, I think, be able to install a Japanese
version and switch the interface language to English. If you are working in
a Japanese environment this might be an option worth considering. If you
already have Japanese 2003 you may know more about this than I do, but,
again, 2003 and 2007 are slightly different here (in particular, individual
language packs are available rather than one multi-language pack for all).
To sum up: I believe it ought to work fine, but that doesn't mean that it
will!
