I have been having the hardest time getting scim to work in linux mint. I first installed it the same way I did in ubuntu:
1. downloaded chinese language files in Language Support; found Language Code with: locale | grep LANG=
2. sudo apt-get install scim-qtimm im-switch scim-pinyin
3. im-switch -z <LANGUAGE CODE> -s scim
4. then enabled asian language support in open office
In ubuntu - this is all that was needed. I had a keyboard icon in the panel and when I clicked it I would be given the list of input methods which I could then choose no matter which application I was using.
This did not work in linux mint. I have been searching and trying different solutions (one was in the scim firefox thunderbird thread) but none have gotten the input working. SCIM has it's setup, I've gone through that and looked for something to activate it, but no luck. I don't quite know what to try next.