Joey_M

Yes, it checks all of those things.
To clarify: It actually does NOT scan for used language strings. It scans for required/suggested language strings. So for example, it reads your acpmenu.json and makes sure that you have all the 'menu__' strings set up.

I'm not sure how the scanner works right now, but I guess it scans the used language strings and checks if they exist in the lang.php file? If so, it should also check for required language strings that the system expects when you add a specific extension/feature/node/etc.
For example, when you add a Node/Item that supports search, you need to add specific language strings for the quick search menu, contextual search menu, etc. All those language strings are not documented anywhere. Another thing to check are the required language string for admin/moderator restrictions in ACP.
There are a few more areas, but I can't remember them now.