[jzgvhskf] Most common languages

English is probably the most common language spoken, not necessarily as a first language, by the world population.  What second language covers the largest portion of remaining people who do not speak English?  Possible candidates: Mandarin Chinese, Russian, Arabic.  This is not necessarily asking for the second most common language in the world if it already has a large overlap with English.

In the U.S.?  Probably Spanish.

The English-speaker should choose this language to learn to maximize the probability of being able to communicate with an arbitrary person.