High Magilar is the language of the mages. The language requires small amounts of sorcery-like magic use to speak (and write) properly, and the ability to use magic to understand. This is no problem for mages, who are born with the abilities required to speak it, but is difficult for other races to deal with. Non-magic users can never fully understand the language. Those that can use magic might be able to learn to understand it, but very few non-mages ever became proficient at speaking it. Because of this, the mages developed Magilar to communicate with "lesser" races such as gondians.
When Gond was destroyed, the mages enacted some rules about the usage of High Magilar. They confiscated all materials that they could find written in it, and very strictly control its use. They use it at official functions and in coded documents. Teaching the language to non-mages is now forbidden. Even speaking it where other races can hear it is discouraged.
Because of its nature, High Magilar cannot be spoken reliably over communicators. Documents in it have to be written physically by the mage since the magic does not work through intermediaries such as typewriters (though such devices may have existed before the destruction of Gond).