Just like in programming, different spoken languages have different capabilities-- certain ideas are easier to express in one language versus another. Some concepts don't even have words across languages. And there's beauty and rhythm, the way words rhyme, so even if you can express the same concepts, the network of how those concepts play off each other is different.

Having shared languages is awesome, allowing people to communicate together. But having only one language would be a great tragedy. It'd be like saying all paintings can only use one color.