Just like people, some dragons can be very shy. Jet here is rather bashful around new people, keeping his eyes to himself far above the heads of his company. His mage does all the talking, although very few people can understand the growling language of dragons anyway.
All mages can understand their familiar’s voice, to a degree. All the beastly chatter has clear meaning, to their partner’s ears – there can even be some crossover with some kinds of animals, so a mage may hear some language in a cat’s meows if his or her own mage is a cat. Or they may not. Especially with cats, they can be fickle things.
Can you learn beast tongues? Yes, with a lot of practice and study. Some develop a knack for it over decades without really ever knowing.