Using WPE Pro, you can hear everything that the opposing faction is saying, while still in-game.
Click to enlarge
First, download WPE Pro from here:
http://doomshadow.com/filehost/files...-_modified.zip
You may need to disable your anti-virus in order to run it. Next, download the filter from here:
http://doomshadow.com/filehost/files/1/language.flt
Once you have done that, launch WPE Pro, and click "Target program" at the top left of the window.
A list of programs will appear. From the list, select WoW.exe
Once you have done that, load the filter by pressing the load button. Select language.flt from wherever you downloaded it to.
Finally, choose your faction and press the on button
You should now be able to hear Orcish if you are Alliance, and Common if you are Horde