I recommend the book "Is that a fish in your ear? Translation and the meaning of everything" [1] which covers all aspects of translation in an interesting and entertaining way.

He describes simultaneous translators as extreme athletes, and I think this article gives you some indication why.

[1] https://www.amazon.com/That-Fish-Your-Ear-Translation/dp/086...

There are some numbers for this in David Bellos "Is that a fish in your ear?"[1], chapter 19.

An UNESCO study of translations between Swedish, Chinese, Hindi, Arabic, French, German and English over a decade showed that 104,000 of the 132,000 translations made between all those languages were translations from English.

[1] http://www.amazon.com/That-Fish-Your-Ear-Translation/dp/0865...