This is somewhat similar to [[ https://phabricator.wikimedia.org/T44102 | special page to list all items without description in a given language ]] but the listing is limited to items in use on the project. Note that the listing should include items referenced somehow and not only the paired item. If the description is not used, then the item should not be included in the list even if other properties from the item are used.
It can be difficult to track all use through Lua scripts, but use of "getDescription()" gould give a clue that a label is in use.
This special page is //not// important compared to a similar page for labels, [[ https://phabricator.wikimedia.org/T104999 | Add a special page at the client that shows which pages are referenced somehow that are also missing labels ]].