The FAQ says
Zimbra Desktop Download and Install FAQ - Zimbra :: Wiki
How to install spell checker dictionaries?
... (1) Download the dictionaries from these links:
(2) Unzip the dictionary package to the "dictionaries" directory. Depending on which OS you are running, the directory location is:
Windows: <install>\win32\prism\xulrunner\dictionaries

I'm on Windows7 home premium italian --
I'm using Zimbra Desktop 2.0 build 10514
I can't find that path... (can't find "Prism" anywhere

I would also like to be able to spellcheck in 3 languages.

Thanks for any help you can give