Private messages extension has its own unread message system where you can add {new_messages} tag to a nav menu item which will then show number of unread messages in nav menu.
- Create a nav menu item using link option.
- URL is to go to user profile messaging tab. Just need to copy the URL for the private messages tab but remove the part of URL where the username is.
- In label option for the nav menu item add test such as: Messages {new_messages}
- Update menu.
