Finding Unused and Incorrectly Used Keys in Property Files
    Finding unused and incorrectly used keys in a property file:
    
      - in a Java view (e.g. Package Explorer), select a set of packages, source folders, projects, message property files, or
      resource bundle accessor classes
- from the menu bar, select Source > Find Broken Externalized Strings
After the search is finished, the Search Result view displays a list of unused keys in the properties files and all incorrect references to non-existing keys.
    
     String externalization
    
     Externalizing strings
     Finding strings to externalize
    
     Externalize strings wizard
     Source menu