Select the Message Bundle Manager tool from the Tool Menu in the Administration Workspace.
Note: If you do not see the Message Bundle Manager tool in the menu, you may need to add it. See How do I add a stealthed tool to a site? for more information on adding a tool to the site.
The Status tab (which is also the landing page for the tool) will display the current number of modified messages as well as the total number of message properties in the system.