Our youngest was a late talker and we used a lot of ASL to communicate as well. He communicated so well with it that we knew everything was OK mentally.
His speech development had been normal until 18 months when he had a serious bout of RSV. After that he really regressed.
Fortunately he had a young friend who LOVED to sing children’s songs. The singing really brought my son back around to being verbal. As some others have commented, since then we can’t shut him up.
Music is a wonderful tool! It involves both hemispheres of the brain, or so I’ve been told.