At the end of the Young Jack Sparrow novel, Bold New Horizions, Jack frees the merfolk commanding their respect and graditude. And when we get to OST, the mermaids are still harsh creatures and Jack was even slapped by a merimaid (Marina? I believe). So here you can speculate Jack's untold adventures with the mermaids.
***This post is just for pure speculation***
Did Jack tried to steal back the trident? Did he love and leave one of the mermaid?
Post your thoughts below.