[@Lyla] Mmm, it would be a unique language created by a pair of wizards, taught to a character instead of the common tongue of the various nations as an experiment. On one hand, the character would be able to do things such as generate thunderstorms with a couple lines or so of speaking, but at the same time would be unable to speak like a normal person. They would be often mute, as literally speaking any words in their case has some kind of magical effect. Saying something like "Hello over there!" might have some odd effect like causing their voice to boom with a great and loud sound like thunder by accident, or something odd such as causing a nearby glass vase of flowers to shatter could happen if they try to say a regular sentence and the words are attempting to communicate that into some effect on the environment. 

So they would communicate through written words mainly, hand signs as well, though in their mental landscape they could communicate with others far more easily and even speak mentally to others they are connected with as part of the RP without causing magical effects around them. 

In essence, a character whose words have power in some sense. 

Blarg, i hope that made some sense...

The character would, however, have been taught to understand the common tongue when it is spoken to them, and to read and write in it as well. 

They could perhaps be taught to speak normally by others over time, or perhaps could teach a few phrases of the language to others to help them learn more magic and such. :P