Brigham, as recorded by Phineas Young, said that the BOM was translated from Reformed Egyptian by the gift and power of God.
"The History of Brigham Young," Deseret News 7, no. 48 (February 3, 1858): 1
This seemed to take the attention of the whole assembly, consisting of more than one hundred; a gentleman requested me in behalf of the people present to give them some account of the book. I commenced by telling them that it was a revelation from God, translated from the Reformed Egyptian language by Joseph Smith, jun., by the gift and power of God, and gave a full account of the aborigines of our country, and agreed with many of their traditions, of which we had been hearing this evening, and that it was destined to overthrow all false religions, and finally to bring in the peaceful reign of the Messiah.