As for the reason why, he hated Yan more after he learned their languages, the reason is because he now understood the way the Yan people called them
And from language comes thought.
And if the language is evil, then the thought would also be evil
Tuge made a vow to the Sky that if one day he has the power, he would eradicate the words of the Yan people, full of characters that is evil and spawn evil
The written Yan language transcribed one of the tribes of the barbarians Yao. But they use the character jackal
The Rong people are birds and beast.
To them, they pictured the people that does not worship their weird culture of worshiping emperor like a god as distant savages hovering on the edge of bestiality
There is also the Di, a northern tribe, were likened to a dog, the Man and the Min, people from the south, is said to be like a reptile
The Qiang had a sheep radical
They called everyone different than them with contempt.