Rashi (from Seder Olam 23): After Sancheriv's fall, Chizkiyah freed the captives that Sancheriv brought in chains ¹ , from Egypt and Kush, in front of Yerushalayim. They accepted the yoke of Shamayim and returned to their land. They built a Mizbe'ach to Hashem in Egypt, and offered on it to Shamayim. In Menachos (109b), some expounded this to discuss the Mizbe'ach of Beis Chonyo, the son of Shimon ha'Tzadik who fled to Egypt.

Rashi: [The language of] Yisrael in Eretz Kena'an (Leshon ha'Kodesh). Radak - they went and returned to Eretz Yisrael, and learned their deeds and language. It says Kena'an, for Kena'an was Egypt's brother; they were Cham's sons. Bnei Yisrael took Eretz Kena'an, and they were strangers to Egypt; now they will return to it as if it is of their brother Kena'an, for they will consider Yisrael to be brothers

Radak: They will believe in Him and swear in His name, and not in the name of idolatry, which they initially believed in.

Malbim: They will swear to Hashem to destroy a city that will veer from him (refer to 19:18:4:2).

Rashi citing Targum Yonasan: The city of Beis Shemesh, which will later be destroyed, it will be said that it is one of them. Yonason translates ha'Heres in two ways. (a) "Ha'Omer la'Cheres ¹ v'Lo Yizrach" (Iyov 9:7, i.e. the sun); (b) Destruction. Yonason learned from Yirmeyah's Nevu'ah.

Radak: They will cling to Emunah in Kel so much, that they will agree that if one of the cities will retract from Avodas Hashem, they will say to it Ir ha'Heres, i.e. they will destroy it.