I haven’t tried this myself but theoretically it should work. It just requires some hacking.
First of all, this involves using qTranslate. If you don’t want a multilingual site, you can always fill only the default language. Then to force display only the default language on the post pages, you will need to modify the core qTranslate file:
http://www.qianqin.de/qtranslate/forum/viewtopic.php?t=1777#p8303
And to enable translation for custom taxonomy terms, you need to create a function:
http://www.qianqin.de/qtranslate/forum/viewtopic.php?f=4&t=2045&start=0#p7380
Hopefully, this will fulfill your needs.