Rabbi Chiya begins by saying that the angel taught Joseph the seventy languages that the Pharaoh knew but also taught him the Holy Language that the Pharaoh did not. Rabbi Shimon says that even though Joseph pretended not to understand the language of Potiphar's wife she eventually caught onto him and knew that he did understand; then the Holy Spirit known as 'testimony' gave him a warning. It is this testimony that is the Hei that was added to Joseph's name and the Yud that was added to the name of Pinchas.
Joseph's greatness was found when he resisted the seductive words and sexual advances of Potiphar's wife, one of the most enchanting women in the world. The inner strength and virtue deeply rooted in Joseph is implanted within us so that we forever triumph over the seductions of our material world.
Pharoah symbolizes man's self-destructive ego. The narrative that expounds upon Joseph's mastery over Pharoah in the Holy Tongue instills in us self-mastery and might, so that we may, at last, triumph over our Evil Inclination. This great Light extends to all human beings. Humanity now achieves its final victory over the angel Satan and his entire legion.
The addition of the Hebrew letters Hei and Yod into the names of Joseph and Pinchas, respectively, indicates the alteration of human nature, the divine aspect of the Creator being imbued into the very being of these people. Here, we too receive an injection of divinity through these two "genetic-like" Hebrew letters. Our essence is forever changed.