My Bela is a former puppy mill mama, and came to me through Sheltie Rescue when she was 5 years old. For the first seven months I had her, she never let out a peep - never wagged her tail, and never smiled. Her eyes were essentially "dead", as was most of her body language. When we got our second dog, it did the trick! One day she just started barking, and I was so happy I gave her a treat for every bark. Soon after, she quickly caught on to the whole concept of communicating and developed a very large "vocabulary" of faces, barks, whisper-barks, growls, half-growls, tail positions and motions, and a big, huge goofy grin!
It was amazing watching her learn to communicate at least one major concept a day there for a while. Even now, she's coming up with at least a couple things a week.
Her most recent is to let me know when she's lost her "road-kill baby". (This is a stuffing-free fox toy that is the same color as she is and she tucks under herself in a nursing position when she settles down for the night.) Of course, losing this toy constitutes a full-out household search and rescue deployment. She lets me know her baby is missing by rapidly stomping backwards about six paces when I tell the dogs it's bedtime. When I start looking for it, she "helps" by using her nose and hunting with me. She usually finds it, which makes me think she knew where it was all the time. But some nights she just gently picks up her "baby" and carries it into her crate, lays down, and begins to groom it before "nursing" it. It's very cute, but makes me a little sad that she was used most of her life for breeding after breeding after breeding. But she's happy, so I'm happy.