We'll create fresh WordPress site with You Have a New (BuddyPress) Message installed. You have 20 minutes to test the plugin after that site we'll be deleted.
This plugin is as simple as it is useful. Add the widget or use the shortcode [you-have-a-new-message]
anywhere to display a notice if the currently logged in user has new messages. The notice links to the user’s inbox as a convenient and omnipresent shortcut.
Message texts can be configured via widget interface and shortcode parameters, e.g. [you-have-a-new-message single="new message" multiple="%s new messages"]
.