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.