In Mosiah 28 we have the story of King Mosiah translating the twenty-four plates through the use of the “two stones which were fastened into the two rims of a bow” (Mosiah 28:13). After telling the story of the translation and the reaction of the people to having it read to them, Mormon noted: “And this account shall be written hereafter; for behold, it is expedient that all people should know the things which are written in this account” (Mosiah 28:19).
Mormon gave no indication that he thought he would provide that information, and we have the book of Ether because Moroni fulfilled his father’s promise that “all people should know the things which are written in this account.”
Although Moroni says that he took his account from the “twenty and four plates,” it is unlikely that he made a new translation. A king and a prophet had already created a translation through the divinely assisted interpreters. There was no reason to do it again. Additionally, if the book of Ether were translated while Moroni was traveling, after the destruction of Cumorah, he must have had the twenty-four plates with him, but then decided not to include them with the plates that were buried for safety reasons. They were sacred records, and ignoring them would have been unthinkable. It is most probable that he worked from a copy of Mosiah’s translation.