Well, I got to know from the Jeppessen abbreviations chapter that GLS is indeed GNSS Landing System, something that our airline doesnt use, hence it is deactivated.
Henry VIII: Since the pb is deactivated, the two windows on the RMP are blank when you press the GLS button.
Cosmic Frog: It could very well be on the A 320. Its just that our 319/321 are relatively a lot newer than the 320s, hence the extra/more uptodate features.