Oddly enough, I find myself agreeing with the Cunctator: English is the default international language. Air traffic control, computer languages, scientific journals and a whole lot more use English to communicate.
Why? Because the world needs a lingua franca, a common language in which everyone can express their ideas.
On the other hand, there are hundreds of millions of people who have no intention of learning English. They will get little or no benefit from an "international" encyclopedia which isn't written in a language they can understand. Maybe that's one reason some people want to make a Spanish-language encyclopedia.
Another reason is that language communicates culture. Spanish-speaking people have different interests and attitudes, on the whole, than English-speakers in general. There's what we might call a "Latino" community.
Additionally, there are those who feel that English is a language of cultural imperialism, intrinsically oppressive and restrictive rather than being responsive to the linguistic needs of non-English speakers. I can't argue with that, if for no other reason than my inability to communicate in any language other than English.
Just some thoughts.
Ed Poor