A peasant (or pedant) writes:...
When the poor in France had no bread to eat Marie Antoinette is reputed to have said ‘let them eat cake’.
The phrase she is said to have used is ‘Alors, qu’ils mangent de la brioche’.
Which has been rendered, imperfectly, by ‘Google Translate’ of the day, as ‘let them eat cake’.
The translator obviously not being aware of French bread-making terminology.