ZCS does not seem to be well prepared for i10n / i18n:
/opt/zimbra/jakarta-tomcat-5.5.7/webapps/zimbra/
js/ajax/config/data
contains a file named AjxConfig.
js which declares AjxConfig.DATE_SEP to be /. In Germany we use . as the date sererator: 31.12.2005.
BTW: Germans don't use AM or PM: My clocl shows 19:51 instead of 7:51PM.