Article 15 Official Language
The Official Language and script of Iran, the lingua franca of its people, is Persian. Official documents, correspondence, and texts, as well as text-books, must be in this language and script. However, the use of regional and tribal languages in the press and mass media, as well as for teaching of their literature in schools, is allowed in addition to Persian.
Article 16 Arabic Language
Since the language of the Koran and Islamic texts and teachings is Arabic, and since Persian literature is thoroughly permeated by this language, it must be taught after elementary level, in all classes of secondary school and in all areas of study.
Article 17 Official Calendar
The Official Calendar of the country takes as its point of departure the migration of the Prophet of Islam -- God's peace and blessings upon him and his Family. Both the solar and lunar Islamic calendars are recognized, but government offices will function according to the solar calendar. The official weekly holiday is Friday.
Article 18 Official Flag
The Official Flag of Iran is composed of green, white, and red colors, with the special emblem of the Islamic Republic, together with the State Motto.