The episode features archaic languages: Old Norse, spoken by the Vikings and Old English spoken by the Saxons. Only Athelstan, Ragnar and Ecbert are able to speak both languages. Ragnar and Ecbert are both taught by Athelstan. Athelstan usually translates. But Ragnar and Ecbert are able to communicate independently with the other language without a need to be translated.
The "p" in Porunn is pronounced as "Th". So her name in English would be Thorunn.