Do Ithkuil. Not only does it look like a cool sci-fi language, but it is also extremely (impractically) information dense. “Tram-mļöi hhâsmařpţuktôx” translates to “On the contrary, I think it may turn out that this rugged mountain range trails off at some point”, and is 5 characters of written script.
But on a more serious note, we would have to do everything we can to ensure that all languages survive, for historical and cultural reasons. You can do things in a lot of languages that you can’t do in other languages, some expressions just don’t work in other languages.
There’s literally no reason to have one global language. If I went to the other side of the world and everyone sounded the same as me I would freak out. Like maybe 5-10 regional languages but preserve all languages and even revive dead ones.