Like many, most of my life I have lived with dogs. They have been my most favorite part of my photography for over 30 years. I love watching animals talk and wanted to share some of my observations ...
The native language of dog (outside of smell which I have no clue about) is body language. Voice / sounds are used for getting the others attention and at communicating attitude, but not so much for conversation. If you want to talk dog it starts with carrying on a conversation using your body. I am not saying don't ever use your voice, dogs can learn language and meaning. Just know that dog language starts with body language.
The base body language conversation is about relationship - attitude. Safety, confidence, expectations, acceptance, understanding.
Your body is your first level dog voice. The direction you are turned in relation to the dogs position. Which direction your head is turned and the angle of your head. Whether you are staring or have soft eyes. Standing or sitting. Walking towards or away. It is all a conversation.
Want your dog to get used to coming? walk away. The next time your dog barks at someone you don't want them to ... don't say a word, walk between your dog and the someone and turn and look at your dog, see how it changes things.
For me, listening to dogs includes with watching them communicate with each other. When two dogs greet for the first time the noses touch or come near each other. In a split second the angle of the heads and eyes in relation to each dog communicates the degree of friendliness and acceptance. Watch that first touch and turn, it is a fascinating conversation.
I don't know all the answers, every dog is different. The joy of this way of thinking is I don't have to know in order for you to learn, I learn everyday. Your dog is the teacher. As long as you continue to do different things with your body to see how the dog reacts your dog will teach you ...being a dog talker always starts with being a good dog listener.