Communication between your dog and yourself does not involve an actually language. After all your dog cannot express what they are thinking in words. However there are several means they use that can indicate what they are thinking. This involves using body language.
One way your fury friend uses body language to communicate with you is by the use their tail. The position of their tail and its motion can indicate a number of things. The position of their tail and its motion could indicate submissiveness, anticipation of being greeted by you or another human friend. The position of their tail and it motion could even indicate potential aggression.