Place a colander in a 2-quart glass measure or medium bowl. Line colander with 4 layers of cheesecloth, allowing cheesecloth to extend over sides. Spoon yogurt into colander. Cover loosely with plastic wrap; refrigerate 12 hours. Spoon yogurt cheese into a medium bowl; discard liquid. Set yogurt cheese aside.
Preheat oven to 350°.
Combine 1/3 cup lemongrass, 6 garlic cloves, and sliced ginger. Remove and discard giblets and neck from chicken. Rinse chicken with cold water; pat dry. Trim excess fat. Spoon lemongrass mixture into body cavity. Starting at neck cavity, loosen skin from breast and drumsticks by inserting fingers, gently pushing between skin and meat; rub salt under loosened skin. Lift wing tips up and over back; tuck under chicken. Place chicken, breast side down, on a rack coated with cooking spray. Pour water into a shallow roasting pan; place rack in pan. Bake at 350° for 1 hour and 55 minutes or until a thermometer inserted in meaty part of thigh registers 180°. Cover chicken loosely with foil; let stand 10 minutes. Discard skin.
Heat oil in a medium saucepan over medium heat. Add onion and curry; cook 5 minutes, stirring frequently. Stir in 1 tablespoon lemongrass, 1 tablespoon ginger, and 2 garlic cloves; cook 1 minute, stirring frequently. Stir in broth and concentrate; bring to a boil. Reduce heat; simmer 3 minutes. Strain mixture through a sieve over a bowl, reserving sauce. Discard solids.
Stir fish sauce and coconut extract into yogurt cheese. Gradually add hot pineapple sauce, stirring constantly with a whisk. Cover and keep warm.
Place a heavy-duty zip-top plastic bag inside a 2-cup glass measure. Pour pan drippings into bag; let stand 10 minutes (fat will rise to the top). Seal bag; carefully snip off 1 bottom corner of bag. Drain drippings into yogurt mixture, stopping before fat layer reaches opening; discard fat. Stir well. Serve chicken with pineapple-curry sauce.