Arbernaut, I have not played with the Chinese side yet, but here are a few comments on the japanese side. As background to the following, i speak and use japanese, my wife is japanese and speaks english, and both my children are bilingual too. All of us use both English and japanese programs and environments on our Macs.
I have 2 g4s, - a dul 500 dVdram and a 867 superdrive, both running OS X.1.1, both run classic at start up:
On the Dual 500 I run english at system level, but as with OS 9 i am able to run native japanese programes, and also input Japanesse into english programs . I have found that there are less progrms that have dificulty displaying the japanese fonts. Kotoeri input system is still not as good as the new Atok14 which is avialable for both OS9 and X. it works brilliantly and i find that it is much more intuitive about Kanji (character) selection.
On the 867 I am running the system level in japanese and have absolutely no problems runnign fully English programs in this environment. Once again, i upgraded to Atok14 as the input and intuitiveness is better.
On both systems you can scroll through different keyboard input using the old Apple/spacebar combination without any problem. Changing the System level language is also easy via the (very easy to use) system preferances pane. You make your original selections when you set up though.
OS 9 programs seem to run better in classic under OS x.1.1 than they did in OS 9 - go figure. I even have a 8 year old version Japanese version of macwrite2 running which runs OK.
I use OS X.1.1 disc supplied IE5 for browising and it renders language pages better than netscape ever did, and i use the OS x Mail application which also is very smooth for japanese (shame it is not much of an email app yet) -. I am trying to get my hands on MS Office v.X which I am hoping will have better multi language support - On balance i think I will go with entourage if there are no language problems. I have both English and japanese versions of Appleworks 6.2 for OS x , so that I can work in it with Menubars and dialogues in japanese or English depending on the requirement, but both handle Japanese input seamlessly. The English version, however, supports saving as a Word doc which the japanese versin does not yet.
As for the appearance, the OS X japanese fonts are FANTASTIC - much much bbetter than the OS 9 osaka etc, and the OS X aqua/quartz systems seem to render them beautiffly.
I am yet to open a document fromt eh PC or internet world in japanese which the new font set could not manage. I will have a dig around on the chinese side and let you know.
let me know if you have any more questions...