John Whitmer says Joseph Smith as seer could translate papyri by "the revelation of Jesus Christ."
John Whitmer, History, 1831–circa 1847, 76, The Joseph Smith Papers website, accessed August 11, 2021
About the first of July 1835 there came a man having four Egyptian Mummies exhibiting them for curiosities, which was a wonder indeed! having also some r[e]cords connected with them which were found deposited with the Mummies, but there being no one skilled in the Egyptian language therefore could not translate the record, after this [e]xhibition Joseph the Seer saw these Record[s] and by the revelation of Jesus Christ could translate these records, which gavee an account of our forefathers, even Abraham Much of which was written by Joseph of Egypt who was sold by his brethren. Which when all translated will be a pleasing history and of great value to the saints.