This Utility will check YaBB language files against lists of what each YaBB version should have in its Language files. (2.6.0, 2.6.11, 2.7.00.) It can also compare two versions of the same language (like YaBB 2.6.0 to YaBB 2.6.11) and the script will tell you which items have been edited.

Instructions: unzip langfix.zip  and upload the contents to your cgi-bin. CHMOD complang.pl to 755 then point your browser it its location. (You may also need to edit the path to Perl if your path to Perl is different.)

To add other languages to check: In the langfix/Lang folder, create a folder for the YaBB language files you wish to check and then copy your language files into that folder. You will need to edit Menu.lng to comment out

require Sources::Menu;
SetMenu(); 

Failure to do this will cause the script to fail as it doesn't know where 'Sources::Menu' is. 
Remember to uncomment those lines when you copy your edited files back into YaBB.

Also keep in mind that items added from mods will appear as 'extra' items when checked against the basic item list. 

You can see it in action Here