Deanna's accent in "Haven" is specifically said to be same as her dad's: "It's amazing how that accent of yours reminds me of your father."
Sirtis tells a story at conventions that she came up with an alien accent for Betazoids. But then Majel Barret wasn't going to do one, and when she asked about it, the producers said, "Oh, well, it's your dad's," and the line was put into "Haven." But then when Deanna's dad showed up, they didn't have him do an accent, either. Sirtis went to Berman about it, and he was basically like, "Oh well!"
Sirtis tells a story at conventions that she came up with an alien accent for Betazoids. But then Majel Barret wasn't going to do one, and when she asked about it, the producers said, "Oh, well, it's your dad's," and the line was put into "Haven." But then when Deanna's dad showed up, they didn't have him do an accent, either. Sirtis went to Berman about it, and he was basically like, "Oh well!"