What do we know about dogs and the way they communicate with human beings?
Scientific American concludes they don’t, at least not really.
Numerous times in fiction, especially in films, dogs can give voice to very complex ideas.
In his wildly popular comic, The Far Side, artist and lunatic Gary Larson hypothesized a very low level of canine understanding (or is it interest in?) of our spoken commands, much less ability to respond verbally.
But human propensity to dress dogs up, babble at them endlessly, and make them into little playthings leads me to conclude that we humans believe dogs can indeed understand, if not communicate in response. Given my long experience living closely in the familiar company of “man’s best friend,” I have come to believe that (1) dogs do talk, but (2) they don’t speak all languages equally well.
Evidence?
There’s a professional dog walker I’ve observed speaking to his pack in a sort of pidgin Gaelic; and they never listen to him. He’s constantly repeating commands again and again, to no apparent result.
I know just what DeeDee would say: “Ca ne fait rien.”
Speaking Plainly 
Our dog, Taffy, a Welsh corgi barks, lightly, for his snacks. He has a different and warm bark for welcoming people. A different determined bark for threats. A quizzical bark when he’s curious. Definitely he communicates. I suspect some of his barks are in Welsh due to his lineage although he is American born and knows how to speak Californian from when he hails. His bark for squirrels in North Carolina is different for seagulls in California. He’s a versatile and entertaining communicator.
Love the boa she’s wearing.