At 0:55 they start singing and I remember a developer stating somewhere that they are singing in dragon language but yeah.. they aren't
It's just English with a distortion effect, they are singing the following
Dovahkiin
Dovahkiin
For? the sake of Skyrim!
For our life, for our home
For Hrothgar's blood
For the Nords and for the Gods,
For the sole single son
Dovahkiin, our king, who'll dawn with fire!
Why did the dev say they were singing dragon language when they clearly aren't?