Let me change that, a traveller expecting to go anywhere and speak their native language is rude, expecting all travellers to learn every destination language of everywhere they go is unworkable. Every employee learning the language of every company and customer, also unworkable. A universal intermediate language that isn’t any nation’s preferred language and hasn’t been part of any colonial efforts in the past, is a possible way to dodge both those things. Not rude because everyone’s stepping out of their home language.

But it would have to be grassroots - if the English government mandated that everyone speak Esperanto in school then tried to spread it round Ireland and the EU it would ruin it. Same if the EU adopted it en masse, Brexiteers would reject it on principle. It could only ever happen if it grew in a balanced way where more and more places distributed around the world use it, and more and more people around the world learn it because it’s useful, and it somehow never becomes one country or one group’s unfair advantage. (That is to say, it can’t ever happen).

Would you still oppose a universal language if it was voluntary, not pushed by one nation into others, and not a replacement to primary national languages?