251. National language.
(1) The National language of Pakistan is Urdu, and arrangements shall be made for its being used for official and other purposes within fifteen years from the commencing day.
(2) Subject to clause (1), the English language may be used for official purposes until arrangements are made for its replacement by Urdu.
(3) Without prejudice to the status of the National language, a Provincial Assembly may by law prescribe measures for the teaching, promotion and use of a Provincial language in addition to the national language.
SOURCE: THE CONSTITUTION OF THE ISLAMIC REPUBLIC OF PAKISTAN