Except you're not even including the value of diversity in your argument.
"Unity" also leads to groupthink and monocultures which are less resistant to new challenges. Unity comes with costs you're ignoring.
Languages aren't just an encoding, but an entire paradigm of thinking. Eradicating linguistic differences eradicates entire perspectives.
Languages aren't just measuring systems. Culture is embedded in them too.
For proof, look up the etymology of a random set of words. They come from all over the world.
This is literally pride over encodings. It’s superficial, petty, and ignorance makes it seem profound and important.
I speak two languages fluently and they really are two different modes of thinking. That's why translation is an art, not a science, and for literary stuff it's quite difficult.
This is why I mentioned the metric system, and what not. Every time throughout history when we decided to unify, the advantages VASTLY, and I mean VASTLY have outweighed the short-term drawbacks.
In fact I'd say, one of the biggest test for us as species is that we can fully understand, internalize and implement this concept. Because we always reach for the short term. Short term profits over long-term strategy in the enterprise. Short term economy benefits over long-term climate impact. And so on and so on.
Someone in Mongolia won't have to switch overnight. Someone in Mongolia may gain the option to have it both ways until they're used to it, and eventually there will be unification. That's basic change management.
Change management is a necessary art to survive and to thrive.