Dragonborn do not wield an ancient Nord power of the voice. There is no such power. Nords have had a special fascination for the language of dragons, and some made an art of speaking it. The art brings power, but that power comes from the language itself, which does not come from Nords, but from dragons. The Voice is called a Nord art only because the practice originated with Nords, thanks to their cultural fascination with dragons and the dragon tongue. Being Nord doesn't give a person any special aptitude in the Voice.
Dragonborn have the souls of dragons, not the souls of Nords. They don't practice the Nord art of the Voice, but speak the dragon tongue naturally.
Right, but there has NEVER been any mention of anyone (other than Nords) ever using the power of the voice.
So it would be a first time thing for any non-Nord character.
It just seems "off" for any race to use the voice, other than a Nord.
