English is the official language of Pakistan. Urdu is the national language. It is also known as Lashkari Zaban or just Lashkari. It is believed to have started in Punjab with Lahore as it's capital during Ghaznavid rule.
Provincial languages
There are also provincial languages, Balochi language, Pashto, Saraiki, Sindhi and Punjabi, and one semi-provincial language Koshur (Kashmiri language).
Background
Pakistan is heir to one of the most ancient civilizations in the world along with Iraq and Egypt. They also had ancient indigenous languages before being replaced by their present-day languages. These languages have not been used in the domains of power because the rulers of these regions were generally foreigners. But the foreigners, whether the Persians, ancient Greeks, Arabs, Turco-Mongols as well as the British, have all influenced the indigenous languages so that their vocabulary is multilingual and varied. As the people of these areas converted to Islam, Arabic and Persian words influenced and became part of their identity, and remain so. In a sense, it is their very presence, as well as the Arabic-based scripts of all 75 Pakistani languages, which gave them a cultural unity.
Linguistics
Linguistically, Pakistan is almost entirely Indo-Iranic as it's languages belong to the Indo-Iranic family of languages. Its scripture and vocabulary owe very much so to Arabic and based on Farsi (which also derived it's own script from Arabic).
For example; the national anthem is a highly Persianized form of Urdu.
Other languages
Other languages include Burushaski, Balti, Domaaki, Gawar-bati, Erina, Wakhi, Shina and Brahvi.