2a) What proportion of the world's literate population can read one of the six official languages of the United Nations (ar, en, es, fr, ru, zh)? 2b) What proportion of the world's literate population can read one of ar, de, en, es, fr, pt, ru, zh? 2c-f) What proportion of the world's literate population can read one of a list of [15, 30, 100, 200] languages chosen so as to maximize the answer to this question?
These seem like even simpler questions (except the last part of 2, which has a difficult optimization problem contained in it). I hope someone can answer them.
You probably need to specify what do you mean by "can read". Say in Wikipedia Babel language proficiency level terms, if somebody "can read" English - do you require for the question 2 en-1, en-2, or en-3 level?
My guess would be that with en-3 to a good approximation it is the same percentage as calculated from the number of native speakers of these languages; for en-2 and en-1 it could make a difference.
Cheers, Yaroslav