From the Mughal Empire to Sikh Empire, Punjabi never had an official status, the language of the courts was Persian. The region was rife with indigenous schools which taught in Persian & Arabic. Apart from education, Persian was also the language of judiciary & bureaucracy.

After 1849, when Punjab became a province of British Empire, Persian was overtaken by Urdu. It was considered the language of lower & middle-working class hence propagated as vernacular for being used in administration & low-level judiciary thus gaining the domain for employment.

English gained momentum as the language of upper-judiciary and upper class in order to occupy the high-societal positions. The British tricked the locals by substituting native languages with English with false sense of participation in running the matters of the state.

Language played an important role for the religious identification in North India. In the 18th & 19th century, the political movement of Tehreek-e-Pakistan propagated Urdu as the Muslim language; a symbol for Muslim identity whilst Punjabi was established as the 'Sikh language'.

Historically, Muslim settlers in conquered lands always used the Arabic script for writing local languages but Punjabi Sikhs believed in the sacred qualities of the Gurmukhi script. Since Pakistan was created on basic principle of one nation, one language, one state;

Urdu became a positive choice for national language of Pakistan even though it was not the language of an indigenous ethnic groups but it was chosen by the immigrants (mohajirs and Muslim Punjabis) who were the leading politicians and advocates of Urdu as an Islamic language.

They predicted that Urdu will weld the difference between the ethnolinguistic groups of Pakistan as 'one nation' & since it is the mother language of small group of people, it would not place any large ethnic group in privileged position however, Urdu faced serious opposition...

from major ethnic groups in Pakistan except Punjabis. Punjabi speaking & Urdu speaking Mohajirs formed a coalition & actively supported Urdu as the national unity in Pakistan.
The discrimination of Punjabi language remains central to difference of class & literacy till this day.