Sonja was a character in the 2003 horror-action movie "Underworld." I'm not going to say so much about her, because it may ruin the movie for some who haven't seen it (what are you waiting for?)
Sonja is also a common Macedonian name. Letter N followed by J make up a letter NJ (as in NEw) in Slavic languages. It is pronounced the same as Sonia or Sonya, not Son-JA as in JAil.
Red Sonja comic books. They take place in the same world as Conan.
Red Sonja is an unbeatable woman warrior who refuses to sleep with any man who cannot beat her in a duel, she purposely wears very skimpy armor to antagonize men who desire her.
I love the way it's pronounced; it's so soft and makes me think of a girl who is sweet and is always laughing and smiling. My boyfriend wants to name his future daughter this, and he's of German heritage as well as I am. I like this spelling, too.
I love this name: its sound, and its spelling--Sonja is my favorite of all its variants. I also like that it means the same thing as Sophia, "wisdom," without being nearly so common (in America).