Thjodhiskmal

Thjodhiskmal is the "Common Tongue" of the North in Midhgardhur, spoken universally by the Danir, Gautar, Northmenn, and Sviar, as well as all their colonists (such as the Rys in the great eastern forests, the Nyjirmenn of the distant western isle of Nyrheimur, or the Vaeringjar who serve as the bodyguard of the Silver Emperor of the South).

Source: The name "Thjodhiskmal" comes from adapted Old Norse roots that mean something like "the language of the people" - Thjodhiskmal is a somewhat adapted and stylized form of Old Norse created specifically for Midhgardhur. It is as close to the vocabulary and grammar of Old Norse as author Colin Anders Brodd was able to make it, but with adaptations so that is can be spelled with the standard English version of the Roman alphabet (no special characters required), and with some deliberate changes in keeping with modern Icelandic in order to make it friendlier and more pronounceable by English-speakers (e.g. the Old Norse inflectional ending -r is replaced with modern Icelandic -ur, hence what would be Midhgardhr is Midhgardhur for ease of pronunciation!)