Everyone has something to say about what language they know how to speak and everyone discusses it in english. That conversation has chased its tail long enough so we are going to move it forward by proposing this:
Which language can the majority of people throughout the world agree to learn as a 3rd or 4th language. Any language. Japanese, arabic, swahili be creative but do not just pick a language for fun. It has to be useful and by useful it must allow people to immerse themselves in another culture and communicate with other people outside of a base language.
The 3rd/4th language would be a collective exercise that most must learn.