[Ibrîniðilpathânezel]

For myself, I have always assumed that everything said about Sauron in LotR is filtered through Hobbits, because they were the ones who wrote the book (according to Tolkien's authorial conceit). Gandalf, for instance, is most often called Gandalf, even though his name among the Elves is Mithrandir (none of whom call him that until Lothlorien, if I recall correctly), Tharkun among the Dwarves (who never call him that), etc. Gandalf is the name the Hobbits knew best for him, and thus is the name that shows up most in the book they wrote that was the chronicle of the War.

Why Sauron would not let any of his servants speak or write his proper name seems rather peculiar, until one considers the power Tolkien ascribes to words in his mythos. There are many beliefs in the so-called real world that ascribe tremendous power and control to knowing another person's true name. Again, if I'm remembering correctly (I have no books at hand, so I'm winging it), the King of the Nazgul learned "black arts" from Sauron, and in sorcery, the knowledge of Sauron's true name, its utterance or its inscription, could permit a kind of magic to be used against him. He would not want anyone, especially his servants and slaves, to have even a chance of interfering with his power by such a means, even if it failed. So, the possibility that The Mouth actually used "Sauron," even though He Himself hated it, would have been preferable to using His true name. It is a small price to pay, allowing this servant to use the name His enemies know best when dealing with them as His ambassador.

Just some things I've thought for a while.