I need to add a translation based on en_GB, but with 24 hour time format. I've copied /opt/zimbra/jettywebapps/zimbra/WEB-INF/classes/{keys,messages}/*en_GB* and /opt/zimbra/conf/msgs/ZsMsg_en_GB.properties to corresponding files named en_EU for "English Europe". I've added a line referencing en_EU to /opt/zimbra/conf/msgs/L10nMsg.properties:
en_EU = English (Europe)

Still, after restarting jetty, English (Europe) is not listed as an option to select in preferences.

I've copied all of my en_EU to corresponding en_IE files, which were not previously present on my server. English (Ireland) is now available, but still no English (Europe).

What am I missing? How would I make this custom localization available on my system?