Whisk together the soy milk and vinegar in a large bowl, and set aside for a few minutes to curdle. Add the sugar, oil, vanilla extract, and other extract, if using, to the soy milk mixture and beat until foamy. In a separate bowl, sift together the flour, cocoa powder, baking soda, baking powder, and salt. Add in two batches to wet ingredients and beat until no large lumps remain (a few tiny lumps are OK).