I'm learning new things even as a native Norwegian speaker, I had no idea 'løve' could be a feminine noun :)
why not "sitter seg"?
No expert, but I believe that "sitter" means that he's already sitting on his tail, and "setter seg" that he is going to sit on his tail and that "sitter seg" is not a good combination.. (but please, anyone correct me if I'm wrong)
Yes 'sitter seg' would translate as sits himself. You wouldn't use that . The lion sits himself on his tail doesn't really work.