This is a problem back dated since Ubuntu 10.10 when they started to use ibus as the default Chinese input software. The problem is when you start typing, ibus will give out Simplified Chinese character. As I born in Hong Kong, I learn and use Traditional Chinese and I hate and condemn Simplified Chinese. It is a very long story and I am not going to explain here at the moment.
To solve the problem you only need to edit one config file:
1) use your favorite text editor and open /usr/share/ibus-table/engine/table.py
2) Go to line 123, and you should read “# if IME declare as Chinese IME”
3) Go to next line, change 0 to 1 if you want ibus to show Traditional Chinese only; or change 0 to 3 if you want traditional first then simplified
4) Save and restart ibus