Edonyms vs. exonyms. Happens in every language. It's especially common when the two sides have difficulty communicating: "What do you call yourself?" "Ger man.

Edonyms vs. exonyms. Happens in every language. It's especially common when the two sides have difficulty communicating: "What do you call yourself?" "Ger man." (Spear man [1]) "... henceforth the lands east of the Rhine shall be known as Germania." [1] This is only one possible etymology.