We will develop different ways of thinking or improve the language we use.
I don't think there is anything in what we currently have that can compare to a united humanity. And this only can happen if we all can understand each others.
I also don't particularly see the usefulness or relevance of everyone speaking one language for the overwhelming majority of people. Do a Chilean farmer, a Mongolian oil worker, and an American programmer need to communicate with each other on a regular basis? And if they did, would this be worth replacing thousands of years of local culture and language?