THE URDU LANGUAGE
For being super close to Hindi, which is the main one, the Urdu language is an Indo Aryan dialect. People speak it in South Asia, mainly in Pakistan where it is the official language since the latter separated from India. It has an official status in several Indian states, and a regional dialect in Nepal.
In the world
Based on what experts say, there are about 66 million native speakers. And if we count those who use it as a second language, there would be a total of about 170 million speakers.
Roots and growth
If Hindi has its roots in Sanskrit, we find Urdu's roots rather in Persian. But both of them come from the sama language group and share a common Indo Aryan lexical basis as well as a rather close diction and syntax. Thus, these dialects can understand each other without too many problems.
It was not until the 18th century that Urdu became a literary language, due to Persian influence from the north. Before that, people spoke another nearby language which is called Hindustani. But, in order to counter the spread of Persian, Hindi soon emerged, based on Sanskrit.
Also, two forms of the Urdu language have emerged in Delhi and Lucknow since 1947. A third standard form also emerged in Karachi. We must add a 4th form in the south, an older one called Deccani. Indeed, the Deccan Sultanates used it at court in the 16th century. At the same time, the East India Company used Urdu rather than Persian throughout North India. This is what allowed it to grow in the 19th century. In fact, religious, social and political factors emerged during the colonial period and led to Urdu and Hindi to separate from each other.
Urdu took the place of Persian as the official language of India from 1837. Until then, Persian and Arabic were taught in Islamic Indian schools to transmit Islamic culture. To educate Indian Muslims in schools, the British then forstered the Urdu language, written in a Persian script. Thus, they considered Urdu as a symbol of their religious roots.
However, the Hindus of northwest India fighted against the exclusive use of Persian and demanded the use of the indigenous Sanskrit. That was led by the Arya Samaj, which triggered a reaction against Hindi written in Sanskrit. This resulted in a division between the latter and Urdu, which became official when Pakistan became a nation.
The Soviet threat
In 1979 occured the Soviet Invasion of Afghanistan which led to the arrival of millions of Afghan refugees in Pakistan. So, many Afghans, including those who moved back to their country, learned and became fluent in Urdu. Indeed, Bollywood films and Indian media often use Urdu, which has helped a lot.
In its less formal way, Urdu is also called "rough mixture". But the more formal register, or "Language of the Exalted Camp", refers to the Imperial army.
The origin of the word used in Urdu often decides how polite or refined one's speech is. Most of the time, people see words with Persian origin more formal, poetic and noble. On the contrary, words with Sanskrit roots sound more personal.
First, due to its Persian and Arabic roots which led to Urdu, we write it right to left.
Second, as the Arabic script is hard to typeset, until the 1980s masters wrote newspapers by hand. In Chennai, a handwritten daily newspaper, The Musalman, still survives like that.
Thanks to Bollywood and media, differences between Urdu and Hindi tend to decrease with time.