Some interesting thoughts on what additional languages an English speaker would find the most useful for travel worldwide: https://travel.stackexchange.com/ques

Some interesting thoughts on what additional languages an English speaker would find the most useful for travel worldwide: https://travel.stackexchange.com/questions/35348/as-a-native-english-speaker-which-two-further-languages-would-give-me-the-most https://travel.stackexchange.com/questions/35348/as-a-native... But you need to make a lot of assumptions as to what is really the "most useful".