Old Norse is a language spoken by the Norse people prior to the rise of Christianity in Scandinavia.
Magnus Chase and the Gods of Asgard
The Sword of Summer
Halfborn Gunderson is shown to speak Old Norse due to being alive during the time of the Vikings.
The Hammer of Thor
When in the tomb of Gellir, Samirah al-Abbas translates the Nordic runes along the side of the coffin.