You knw, we have been observed our dog's tail for a long time.
SO the conclusion is: he wags his tail when he is happy, when we approaching him for playing...but something very discouraging is..
he wags his tail even though he is barking at his enemy
One precise identification on my dog's emotion is: his ear.
If he is happy, his ears always standing.
If he is being scolded by my mum, or we are talking bad about him, he knws tht, his ears would appear in fall-backward.
Try figure it ....