He probably didn't decipher it. The entire line is as an in-game comment:
Dying unintelligble whisper of approximate length to get across "Don't trust LeChuck. He hypnotized a bunch of monkeys and ran me through with my own blade."
It still doesn't make sense. Unless she was going to say, "Jacques told me, 'LeChuck hypnotized a bunch of monkeys!' and then he [LeChuck] ran me through with my own blade!" which I guess could make sense. But she said Jacques told her something and it seems somewhat noncontinuous for that to have been the actual line.
Comments
Perfect last words. I shall be saying this every five minutes on the off-chance I die, for the rest of my life.
You were RIGHT!!!