Dragnix.Net

In movies and litterature there is always those dragons that claim their names "can not possibly be pronounced in [our] language" and then the character have to find up a usable name.

This begs the question of their real names?

I would guess a series of high and/or low frequency tones inaudible by our narrow range of hearing and speech. Not really complicated, but just out of our range to attempt.

Mmmm possibly. Although it may be an effect due to our different vocal throat geometry... some sounds are only possible to pronounce when your throat is a certain shape to get the correct airflow.