It's not a well-liked view, but I'm very glad that humanity is on the path to speaking only a few languages (or perhaps just one). If you disagree, consider this thought experiment: Imagine if the entire world spoke a single language. Would we ever want to invent new languages, making mutual communication harder? It would be silly. I do feel for the speakers of these dying tongues, but in the long run, this is a good…
We do something similar to that already. Kids make up their own lingo when playing, subgroups invent new slangs within a single language, areas make their own dialect, we invent new cultural languages (e.g. music genres) that differentiate us from others, we invent new computer languages despite having existing ones, etc. Heck, even English got developed while other languages already existed.
But that's a question for an alternative reality. It doesn't answer whether it would be better to remove historical languages, and adopt a single (existing or new) one. What I mean is that what would be the best approach in a world that spoke a single language does not really enlighten us about a world that already has many. The world that "spoke a single language" wouldn't have existing living cultures in different languages like us to remove, and thus they'd have nothing to fear of losing.
Besides, languages encode ways of thinking and the culture/history etc of its generations speakers, something that will be lost in a monoculture. Single language = single universal culture = same shit all over the world, no diversity.
And if you think you're still getting diversity within a single country (e.g. because you have stuff ranging from Metallica to the Residents and from Hank Williams and Beyonce to Philip Glass and John Zorn) then you really don't know what actual cultural diversity is.