Hindi is an Indo-Aryan language with about 545 million speakers, 425 million of whom are native speakers. It is the main language used in the northern states of Rajasthan, Delhi, Haryana, Uttarakhand, Uttar Pradesh, Madhya Pradesh, Chhattisgarh, Himachal Pradesh, Jharkhand and Bihar. It is spoken in much of north and central India alongside other languages such as Punjabi, Gujarati, Marathi or Bengali. In other parts of India, as well as in Nepal, Bangladesh and Pakistan, Hindi is understood, and there is a significant number of Hindi speakers in South Africa, Mauritius, Fiji, Suriname, Guyana, Trinidad & Tobago and Nepal. In Fiji people of Indian origin speak Hindi, and in some areas the Fijian people also speak it.

Hindi, written in the Devanagari script, is one of official languages of the government of India - the other offical language is English. Both languages are used in parliament, in the judiciary, in communications between the central government and state government, and for other official purposes.

Linguistically, Hindi and Urdu are two registers of the same language. Hindi is written in the Devanagari script and uses more Sanskrit words, whereas Urdu is written in the Perso-Arabic script and uses more Arabic and Persian words. Hindi is the most commonly used official language in India. Urdu is used as an additional official language in some states and is one of the 22 official languages of India.

Sources: http://www.omniglot.com/writing/hindi.htm
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