Is sign language a real language?

"We can tell friends and family something about his development, but his ears won't change."

"What I really miss for Sofie now is contact with older deaf people. I organized something for that myself."

"It's amazing that we can be in two worlds, the deaf world and the hearing world."

"When Guus was three years old we were taught sign language at home."

"The deaf school turned out to be great for me, actually."

"My hearing children are learning sign language and spoken language at the same time."

"We used to take a quarter to the neighbor's house, to ask if they could make a phone call for us."

"I had to sign in public for the first time -- that was quite a big step."

Why are there so many variations of signs?