I did some research, and found out that ALL of the fruits that you can make with the fruit changer are REAL fruits, including the mangosteen, the cloudberry, and the whortleberry! Who'da thunk?
A close relative of whortleberries grow here in north east of the US - we call them blueberries. The wild blueberries around here are usually smaller than the size of a pea; the ones at the nearby orchards here are the size of grapes. We usually go blueberry picking sometime in July - the season for them here is early July to mid-August. the ones we don't eat right away we freeze by spreading them out on a cookie sheet so they don't stick together and putting them in the freezer, then once they're frozen, we dump them into quart-size ziplock bags and throw them back into the freezer for later months.
Levee, Cloudberries are very common here in Scandinavia, but they only grow in the mountains, and have never been successfully cultivated, as far as I know. They are mostly picked in the wild, and so are quite expensive. They have a very pleasant but subtle taste. You can also get cloudberry wine! (Maybe a Glitch idea?)