There is absolutely no need for what you are suggesting.

The world has always had different languages since before even the beginning of recorded history, we generally just choose one of them as an intermediary, so that people are free to use their own language 90% of the time, but can reliably count being able to use a second language when the need arises.

In other words, we already have 'one language' that we use to communicate cross cultures, and none of us have had to stop using our own language in the process of learning it. What you are suggesting would actually be an incredible amount of effort towards putting ourselves in a situation with no practical or logical benefit, it would be like suggesting everyone would find it easier to have one arm when they already have two. It is like trying to suggest that bilingualism is a burden, rather than a blessing.

The unique position that English speakers have, is that since English is that language for the time being, we almost suffer from the effect of 'tyranny of choice' when choosing a second language to learn. In the times when French or Latin were used as international languages, not learning them would have been a sign of someone having very poor education, however now, lack of ability in foreign languages is pretty much the norm, and from this position, where most people have no perspective on how empowering it is to speak more than ones own native language, we find that people seriously suggest everyone else should do away with their own, for the sake of making our own lives easier than they already are.