Dragons have their own language with little variation amongst the species. They don’t share this language outside of themselves, not even with their riders.
Dragons aren’t capable of understanding the speach of the bipedal species of Keverynn, nor can they speak to them. Gold dragons are the exception as their innate gift is universal language. Dragons who have Chosen a rider gain the ability to understand the language spoken by their rider.
Wild, unpartnered dragons generally don’t bother with two-leggeds, but sometimes help the Dragonlords, particularly if their mate has a rider or they’re related to a partnered dragon. Some who help have no affiliation with a rider’s dragon. If they need to communicate with a two-legged, they use a paired dragon as a translator.