In a saucepan set over moderate heat, combine coconut milk, sugar, cardomon pods, lemon grass, ginger and vanilla. Bring to a simmer and let cool. Chill, covered, overnight.
In a bowl, combine the tapioca with the water and let mixture sit for 45 minutes. Drain the tapioca. Strain the coconut mixture. In a saucepan set over moderate heat, combine the tapioca with the coconut milk mixture, bring to a simmer and cook over low heat, stirring frequently, for 10 minutes, or until thickened. Transfer to a bowl and stir in the cream. Let cool and chill, covered, until cold. In a bowl, combine mango with orange juice, lime juice and sugar. To serve: Pour coconut mixture into soup bowls then arrange mango mixture in the middle of each bowl. Garnish with mint leaves.