yes "what you say" or "speak" really good for training a dog when to bark and when not to. So you can teach "Quiet" for the inbetween time when dog is waiting for you to give the next "speak" command, but you start by teaching "speak".
Dogs (my dog?) seem pretty canny when it comes to working for a treat. If they know whatever it is done on command - will bring a treat, they learn to do it - only on command - well not exactly - if something exciting and bark worthy goes past - she's going to start barking again, but if it's dinner we're excited about, then "speak" bark > treat, or even bark "speak" treat, will teach the dog the "speak" command, and then mine - will only bark (or growl) just enough to get the treat. She gets louder if you delay the treat...
So I say "what you say" and she goes - very quiety - "rooow", and if I then say "louder" she get a little bit louder, and if I say "louder" again - she barks. Cos she wants that treat. She knows "what you say", I doubt she understands "louder" but she knows if she doesn't get the treat, she needs to speak up.
So if she's barking her head off at the neighbours come home, I get her attention, show her a treat (sometimes), and ask her "what you say?", and she goes back to "rooww". Much quieter. And she gets a treat and I've completely distracted her from what she wasn't supposed to be barking at in the first place.
And it always amuses kids at the oval.