The Arabic language became more widespread in Egypt with the introduction of Islam, especially since there was only one Egyptian language.
The Coptic language was limited and unofficial, followed by the official Greek language, and then the Arabic language entered Egypt starting in the seventh century AD/ first Century after Hijra.
Arabic is a rich and complete language and the people were able to express everything using it. Arabic became the language of the diwan, or council of ministers, and the language of instruction.
With the advent of the tenth century AD, fourth century after Hijra, Coptic scholars started to compose theological works in Arabic, which indicates that Arabic had become the prevalent language of scholarship.
The Coptic language lost its importance totally during the fourth century after Hijra (tenth century AD), as we find the Coptic books by Said Ibn Al-Batreek and Sawerace Al Ashmony were written in the Arabic language although they were intended for a Coptic audience.
The spread of Islam and the Arabic language in Egypt was helped by Caliph Abd al-Malik Ibn Marawan's arabization of the "Mint" and "Diwans" in the government offices in year 78 after Hijra The Copts were forced to learn the Arabic language to keep their jobs in the government offices. Then Abbasid Caliph Al-Mustasim decided to lay off Arab employees from the government offices. The Arabs and the Copts became equal and the obstacles between the two sides were removed. The Arabs then spread among the Egyptians.
Within 400 years, from the Arab conquest of Egypt, Egypt abandoned its national language totally and adopted the Arabic language, while other Muslim countries such as Iran did not give up their national language.