I like that people feel comfortable enough with me to ask questions that they think are stupid -even though the truth is they aren't stupid questions at all....
Question : "I want to ask you what exactly is the language that Eric's uses?"
This was my answer ...
From Vikings wikia.com
Old Norse is the North Germanic language that was spoken by inhabitants of Scandinavia and inhabitants of their overseas settlements during the Viking Age, until about 1300.
It evolved from the older Proto-Norse in the 8th century and evolved into the modern North Germanic languages after the Viking Age.
Most speakers of Old Norse dialects spoke the Old East Norse dialect in what are present-date Denmark and Sweden. In texts which date from Medieval Icelandic time, writers wrote with Old Icelandic and Old Norwegian dialects. These dialects derive from the Old West Norse dialect.
No clear geographical boundary exists between the two dialects. Old East Norse traits were found in eastern Norway and Old West Norse traits were found in western Sweden.
Some consider Old Gutnish, sometimes included in Old East Norse because it is the least known, a third dialect since it shares traits with both Old West Norse and Old East Norse and also has developed its own.
The Icelandic Gray Goose Laws states that Swedes, Norwegians, Icelanders and Danes spoke the same language, dǫnsk tunga. Speakers of the eastern dialect, spoken in Sweden and Denmark, would have said dansk tunga (Danish tongue) or norrønt mál (Nordic language) to name their language.Gradually, Old Norse splintered into the modern North Germanic languages: Icelandic, Faroese, Norwegian, Danish and Swedish.
Modern Icelandic is closest to Old Norse. Written modern Icelandic derives from Old Norse/modern Icelandic phoneme system. Contemporary Icelandic-speakers can understand written Old Norse, which differs slightly in spelling as well as semantics and word order.In the True Blood TV show Alex Skarsgard is just speaking his native Swedish but in the books Charlaine Harris describes Eric's language as being a very old Viking language that probably would have been spoken over 1,000 years ago.
Alexander speaks Swedish( his own native language) as Eric in True Blood
Examples from episode 4 and episode 12
Eric speaks in Sookie Books
"Eric cursed in a language that probably hadn’t been spoken out loud in centuries" bk8
"He shouted something in a language I'd never heard, and he closed his own eyes" bk4
"Eric said, smiling. He had a slight accent. English was not his second language, of course; it was maybe his twenty-fifth." bk 5