I forgot that Jean Henry is the pirate. His dialogue is muddled and difficult to understand, even in English (he's supposed to be drunk). The reason for the duel is miscommunication; you cannot understand what he says, and he grows more and more angry.
For example, here is a GREETING from his dialogue:
"Yeh reddy ah viset liftaftah?", which would mean "Are you ready to visit the afterlife?"
When the player asks, "Who are you?" he replies:
"Whomam aye? Dreaded scurge of oceansandseas ya!" which means "Who am I? I'm the scourge of all the oceans!"
If you read the player respones, they consist of inquiries like, "Are you angry?", or "What are you trying to say?" and finally, "You want to duel". Jean Henry has to repeat the dueling location several times before the player understands (again, just an attempt at humor).
The translation is not important in this instance, because Jean Henry's speech is not meant to be understood. He is a drunken fool with a quick temper. His dialogue at the dueling site ends with, "uhs parats fet derty!", which means: "We pirates fight dirty" (several pirates ambush you when the duel starts, which is against the rules - not that pirates care about rules!).
Sorry for the inconvenience. Jean Henry is meant to be an entertaining opponent. Feel free to alter his dialogue as you see fit. As long as it's difficult to understand, then it's true to the character.