I think that is a reason the catholic Church still uses it for things like papal encyclicals. It puts different groups on a more equal footing.

Far more people understand it than things like Esperanto. Quite a lot of people know it a bit. I did it at school. My kids learned some (their choice to do it up to GCSE level).

That said, in practice, English is the international language. It is what is most likely to be used at an international conference in most fields, or when people with two different native languages speak.

English is the international language now. About a century ago, the lingua franca of the technological world was German. Half of my father's university text books were in German, pretty much all of mine were in English. Things can (and do) change.

English is a living language so it's a bad choice (at least from my criteria ;) )