I admit there will be a few problems with this, so the first thing to make a bit more feasible would be to make the language very easy to learn, this would probably exclude any natural language from the search. This leaves us with only conlangs, but that is still too wide a net to cast, since some of these are made to feel natural, this will make them unsuitable for this purpose.
I think there is a few languages that could be used for this, however I might know of all language that could fit this role, I really only think Esperanto or toki pona, though I am sure that there must be a few more.
Just I am not familiar with others.
Besides now we have found a language we can start with, would it be possible to create enough content to entice enough others to learn the language to make it have an impact?
My goal would be to create a language that would be spoken by a vast majority this would make international communication much easier. But how would any body be convinced to learn a new language, lofty ideas such as the general improvement to humanity will not be enough to convince most people.
So far it is mostly a dream, how great it would be if every body just comprehended each other?
Belief or not, we could all speak an international language, at least in Europe but guess what one country decided to not be in favor.
First France decided not to support Esperanto as an interlang, but then both the Nazis and the Soviet also decided it was not meant to be, even some
initial success, but that was not meant to be.
English seems to be an almost useful language, but then it is not exactly that widely used.
Would it not be great if we could all just speak one language?