If this is common knowledge I completely missed it. So I post this in memory of all those who also slept through indecent chunks of early morning Seminary.
Mosiah 1:3-4 reads as follows:
3 And he also taught them concerning the records which were engraven on the plates of brass, saying: My sons, I would that ye should remember that were it not for these plates, which contain these records and these commandments, we must have suffered in ignorance, even at this present time, not knowing the mysteries of God.
4 For it were not possible that our father, Lehi, could have remembered all these things, to have taught them to his children, except it were for the help of these plates; for he having been taught in the language of the Egyptians therefore he could read these engravings, and teach them to his children, that thereby they could teach them to their children, and so fulfilling the commandments of God, even down to this present time.
It seems to me that this strongly suggests that the Brass Plates were written in Egyptian of some kind. In which case, one wonders how widespread the practice was. I seem to recall that the Hebrews during that period were really big Egypt fans, much to the chagrin of the prophets.
Also, if you were going to have a semi-regular feature at T&S for short little things one notices in the scriptures like this, what would you call it? Winner gets a No-Prize.