Anthony,

I think the cammand
          $ sudo koha-translate --install zh-Hans-TW
did not take latest po files from
http://translate.koha-community.org/zh_TW/312/.
Am I right? or something else I missed.

 
No, that command do not download new versions from translate.k-c,
it uses the ones under po/ directory.

But you can download manually from translate.k-c and replace the files
manually.

Regards,
Bernardo