They clearly hear human language and recognize that it would be useful if they could do the same thing. Their anatomy does not allow them the articulation to form words, but do what they can and the result is barking. I think dogs have picked up on the value of oral language to humans and have reinvented it for themselves. Barking is their attempt to reverse-engineer language. And they use it much like we use language.
Dogs use barking to communicate with each other and to communicate with humans.
This discussion will continue next week. Stephen Zaillian writes the screenplay as well as directs an excellent supporting cast in a true and realistic story of a civil action case. The film may even sacrifice dramatic impact for accuracy. This may well not be the story the viewer is expecting, but it will be an education in how the law works. The latter he also directed.