Mosiah 1:4; 1 Ne. 1:2
“Lehi’s forefathers were not natives of Jerusalem. We learn in Mosiah 1:4 that certain plates were written ‘in the language of the Egyptians.’ Nephi informs us (1 Nephi 3:19) that these same plates were in ‘the language of our fathers,’ and that the possession of them was necessary if a knowledge of that language was to be preserved among his people… . The language of Lehi’s forefathers was a foreign language; and when Nephi tells us it was the language of the Egyptians he means what he says.” (Hugh Nibley, Lehi in the Desert, p. 26)
“The statement that ‘Lehi, … having been taught in the language of the Egyptians therefore he could read’ the engravings on the brass plates of Laban quite clearly indicates these plates were written in the Egyptian language.” (Daniel H. Ludlow, Companion to Your Study of the Book of Mormon, p. 173)