The only time a person who is not a cleric (deacon, priest, bishop) may be speaking a homily is when they are a translator for the cleric who is actually giving the homily.
The Homily begins after the gospel is finished, and before the liturgy goes back to the book… nothing else is allowed in that window.
This translation is done routinely for deaf persons, and in the case of some foreign clerics. In the latter case, it’s usually not simultaneous, but Preacher then translator, repeat. This has been done on some occasions with the Vatican masses; in some cases, HH Benedict has read it in one, then in another, etc; in others, he’s said it in one (German, English, Latin, or Italian), and had translators read copies of it; some of the translators could not be clerics (one was a woman).