Zimbra is great
UI control for language override. I know that Zimbra does auto language detection but a UI control would be very handy. The reason why: I work in italy but I don't know italian. :) If you use our company as a test, this a actually a fairly common occurance. Give the control back to the user to select language.
Zimbra restarts take foooooooooooooooooooooooorever...
User's control the language. It's based on your browser setting. So it's fully in the user control.
What verison are you running? How long does a restart take? Why do you have to restart so offten? If you just need a cache cleared or something you should just restart tomcat. It should be in very rare and exceptional cases that you have to reboot or restart all of the zimbra processes.