To view chinese characters you don't need the firmware (main). only the FS and the custpack.... but if you want to write you need both....... or like you said the t9, lng and ttf files...... not really sure, but I think this thread may be of use to you
how to add languages to your phone - Top Sony Forums
Looks like you can take the files from other firmwares... and send them into your phone via FAR manager...

cheers,
Kam