Why does it say "Edus bi'Yhosef Samo"?
Sotah 36b: Gavri'el came to teach the 70 languages to Yosef (a requisite to reign in Egypt). Yosef was unable to learn until a Hei from Hashem's name was added to his name 1 - "bi'Hosef Samo b'Tzeiso Al Eretz Egypt." Rashi - this was on Rosh Hashanah.
Radak: Hashem set this Chok of Teki'as Shofar for a remembrance and testimony. Yehosef and Yosef are the same, just like Yochanan and Yehochanan, Yonadav and Yehonadav. All of Yisrael are called Yosef - "v'Yikarei Vahem Shmi" (Bereishis 48:16), "Noheg ka'Tzon Yosef" (above, 80:2), "She'eris Yosef" (Amos 5:15).
Tzitz Eliezer (19:40): Tiv Gitin, citing R. Levi Yitzchak, says that while in the womb, he was called Yehosef. In the womb, he knew the entire Torah. Gavriel wanted to teach him the 70 languages via the power of knowing the entire Torah. He needed to return to him the letter of the name he had in the womb.
What does "b'Tzeiso Al Eretz Egypt" refer to?
Rashi (based on Sotah 36b): Yosef left jail, [to rule over Egypt]. Malbim - this was when Pharaoh had his dream, and the famine and satiation were decreed.
Radak #1: It is when Yisrael left Egypt. It says "Al Eretz Egypt", for "u'Vnei Yisrael Yotze'im b'Yad Ramah" (Shemos 14:8).
Radak #2: It is when Hashem went on Egypt to redeem us - "Ani Yotzei b'Soch Egypt" (Shemos 11:4).
Why does it say "Sefas Lo Yadati Eshma"?
Refer to 81:6:1:1.
Radak: When He redeemed us, I heard them speaking another language that is not my language - "Beis Yakov me'Am Lo'ez" (114:1). I would not have known it, had I not been enslaved to them. Most of Yisrael did not understand Egyptian; they spoke Leshon ha'Kodesh. In Egypt, Yisrael did not change their language or names (Shocher Tov).
Malbim (7): Even though openly, Pharaoh said that he freed Yosef, really it was Hashem's word.
