It seems like you missed one critical category.....
"Second language" language use by population
I personally considered the same question, except that I wanted to know second language by location.
I am from the US and speak four languages. I wanted to know if I traveled, where in the globe would be most difficult with English/Spanish as a first or second language.
Totally agree with you. Second language statistics are a bit harder to track down. It's something I'll look into. English as a second language is probably your biggest help. I'm not sure of any countries that consistently teach Spanish as a second language outside of the Americas.
"Second language" language use by population
I personally considered the same question, except that I wanted to know second language by location.
I am from the US and speak four languages. I wanted to know if I traveled, where in the globe would be most difficult with English/Spanish as a first or second language.