Board Thread:Show-Related Questions and Answers/@comment-27308670-20161104192029/@comment-25926288-20161104194031

It's just a convenience of storytelling. Technically any world should be speaking gibberish to you, but that wouldn't be enjoying. So any fantasy writer writes in the language they speak.

Technically there are other languages in Once Universe but they don't focus on it. Plus most realms are Alternate Earths with stories written in English. Alice and Wonderland books had Wonderland citizens speaking English, as did Baum with his Oz books, etc.