As his left foot is correctly rigged you can check how it works. Notice that there are actually 2 bones overlaying on each foot, they are called Toes Control (R and L) and Toes (R and L). So to make it simpler, switch to Pose mode, hide the bones called Toes Control (R and L), then switch your mesh to Weight Paint mode and check how Toes (R and L) influence your mesh. You can see that Toes.R, contrary to Toes.L, has no influence. So begin to paint the area that is supposed to be influenced by this bone, exactly like Toes.L influence the left foot. You're good.