That's an ability. It's only real use is in dialog. If you attempt to cast it you see an animation but it doesn't do anything this way.
To learn you need a charisma of at least 16 to ask "My apologies, but I can't understand you. Would there be a better way for us to communicate?" or you need to speak with Hargrimm and ask him how he understands her. Then you can ask Stale Mary about his response.
No locked doors, no windows barred. No more things to make my brain seem SKARD.