User blog comment:J Fan/Pirates 5 sails to D23 2015!/@comment-12809866-20150816161326/@comment-1984959-20150817123017

Sorta. According to an interview with Depp in 2014...
 * "So I have high hopes for that 'Pirates 5' because if that's really the last one, which it probably is, I feel that we owe it to the audience who went and saw the films so many times. We’ll do it right and end it on a high note."

As you can see, he implies it's his last one but the film has yet to come out. But who knows, I thought OST was the final one, and look how that one turned out. That being said, I do think there is a strong chance this is the last.