Preheat oven to 350°F. Liberally grease and flour a 12-cup Bundt pan.
Make cake: In a medium bowl, sift together flour and salt; set aside. In a large bowl, with electric mixer on medium speed, beat butter, sugar, and lemon and lime zest until pale and light, about 5 minutes.
Add eggs one at a time, beating well after each. Gradually add flour mixture, just until blended. Stir in soda.
Pour batter into prepared pan and bake until a toothpick inserted in center comes out clean, 1 hour and 15 minutes. Cool completely in pan on a rack before inverting onto a plate.
Make glaze: Stir together confectioners' sugar, butter and juices; add more juice or sugar if needed. Spoon glaze over cake, distributing evenly. Garnish with lemon and lime zest, if desired.