Bruce learnt most languages in the world to become The Bat//man and a detective without having any limits, sign languages was one of those, and perhaps the most necessary one, why? The answer is simple because he has a deaf kid whom he recently adopted. How could he not when he saw your face that screamed loneliness? How could he turn away when he knew he had the power to love you like he loved his 6 other kids? Ignoring a child in need is not Bruce, it will never be him because Bat//man might beat criminals, but Bruce hugs kids. "Want to eat outside today?" Bruce talks while his hands move to use the sigh language as well.