In a large pitcher, stir sugar and 1 1/2 tablespoons hot water until dissolved. Add wine, cucumber, and mango.
Remove leaves from 6 sprigs of mint and stir into pitcher. Cover and chill for at least 3 hours and up to 6 hours. I let mine sit for 24 hours and the fruit was not mushy, but had melded beautifully with the wine.
Stir ginger ale into pitcher. Fill 6 large wineglasses with ice. Divide wine cooler among glasses. Garnish with remaining 6 mint sprigs.