I find answers acceptable in the following order:
- Name from the script of Thor: The Dark World.
- Name specific to this language in Marvel comic books that make mention of the dark elves.
- The correct name as it would be in Norse mythology (some variation of svartal- that I don't know enough to figure out).
Very good answers might provide all 3 versions.
I've only been able to find articles with Eccleston complaining about how tedious it was to learn it for the movie.