In terms of language setup and localization, my computer setup is as follows.
I have English language Windows 7, set to the UK version. When I run Microsoft Office Word it defaults to UK spelling.
When I setup the computer, I added a Chinese Simplified input system which allows me to select Chinese when I want to type Chinese text directly.
For my Trados system, I default everything to US English, and most of my templates are in US English. This is because I've found it easier to work in US English and change to UK English later than go the other way round, especially because I've got a lot of US clients. I've talked before about the problem with sub-languages in Trados wherein I have to copy my US TM's into UK English before working on a UK file which is really annoying. Especially as SDL (who make Trados) seem to spend their time making new versions with pointless features (just my opinion) and higher prices, rather than making the existing programs more workable. Having said that, I think the Windows 8 / Tablet revolution will mean we'll need changes in the way we Translate and I look forward to seeing how the big CAT companies cope with it.
One thing I rarely do is input directly into Traditional Chinese. That's just because I never learned to type using bopomofo and my keyboard doesn't even have the markers. I normally just do it in simplified and then use an on-line converter to turn it into traditional when necessary.
Today, I decided I'd need a pinyin version of Traditional Chinese input (i.e. allowing me to enter traditional Chinese the same way I currently use Simplified Chinese). I came across a great link on Pinyin Joe with all the details. I'll let you go to his page to figure it out if you're planning on doing the same thing.