This is a short post describing how I’ve installed a new language pack to a Zimbra (ZCS) 5.0.10 installation to enable norsk/norwegian language.

1. Download your desired language pack, in my case it was a Norwegian translation from the I18N/L10N – Translations Zimbra forum.
2. Unpack the translation files
3. Copy the translated files to your Zimbra server installation

   # cp *Msg_no.properties /opt/zimbra/jetty/webapps/zimbra/WEB-INF/classes/messages/ 
   # cp *Msg_no.properties /opt/zimbra/jetty/webapps/zimbraAdmin/WEB-INF/classes/messages/ 
   # cp *Keys_no.properties /opt/zimbra/jetty/webapps/zimbra/WEB-INF/classes/keys/ 
   # cp *Keys_no.properties /opt/zimbra/jetty/webapps/zimbraAdmin/WEB-INF/classes/keys/ 
   # cp ZsMsg_no.properties /opt/zimbra/conf/msgs/ 

4. Restart Zimbra

   # su - zimbra 
   # zmcontrol stop 
   # zmcontrol start 

5. Set the language preference in your browser and reload

Please note that since this operation will most like have to be repeated the next time you upgrade Zimbra. Mainly because Jetty changes version and the file location changes making the translated files unavailable.

Source: http://wiki.zimbra.com/index.php?title=Translations#Installing_Translations_in_ZCS_Server