I thought it was neat that Esperanto was used in the books. I first learned of it in about 1980 from a book belonging to a friend's father, who was in the military. It was called 'Esperanto: The Aggressor Language", because it was used by the US Army in their training games.

I GM'd a game of https://en.wikipedia.org/wiki/Fringeworthy where I had the UN exploration teams use Esperanto as a common language.