When I released TextMate two years ago it was intended as a source code editor, and choices made during development reflects that, like its bias toward fixed width fonts and western input methods.
It has since surpassed my wildest expectations about what it would be used for, though until recently, CJK was still not an option.
But devoted users have made CJK bearable, the “hack” comes in two parts:
A bundle by Hans-Joerg Bibiko with an input CJK command. This pops up a control where you can type the CJK text to be inserted.
2006-11-12: There now is a CJK-input plug-in.
I still hope to offer real CJK support in 2.0 (but please don’t send me hate mail if I do not come through). I am 90% decided on switching to CoreText for text rendering (and making 2.0 Leopard only) and when doing so, I will get rid of current text rendering limitations. The CJK input part is more tricky, but now that I have Apple Technical Support Incidents at my disposal, I am slightly more optimistic.