Terry:
Bible writers, translators, redactors and such did this as well when talking about locations, people, names and events!
mP:
Your affectionate nickname for your mum, would never be used by anyone in your family to dictate a public account equivalent to the gospels. WHile i can understand some people particularly in a close group have pet names and so on its highly unlikely that the majority of them do. Are we to believe that everybody always used names from another language and so on in the style we see of the characters in the NT ?
The- best counter to that, are the names of early communists like Stalin, Lenin but even then their true names were still written. In the bible we see something quite different.