The main theme for Last Epoch sung in Old Norse. Here is a podcast about the creation of the theme, and here is a write up of the theme. This trailer features an instrumental version of the theme as the underscore.
Female Vocals: Ffion Elisa
Male Vocals: Colm McGuiness, Mason Lieberman, Matt Lambert, Erik Desiderio
Composer, Tagelharpa, Djimbe, Charango, Seed Pods: Erik Desiderio
Cello: Mason Lieberman
Old Norse Translation Assistance: Nikolaj Reimer Hansen, Dr. Jackson Crawford