Interesting list. I can certainly agree that Russian is a difficult language to acquire for native english speakers; far harder than Spanish.

I am curious, however: has anyone found nonobvious ways to make money with language skills (obvious meaning translator, etc)? While some of these, esp eg Arabic or Russian, might be very interesting to learn, and it would probably be a great experience living in an Arabic speaking country, there are high costs -- the education and the time living in a country and not getting much done but language courses. What are good ways of making this a financially sound thing to do, or will it always be solely a cultural experience?