I'm referring to this accepted answer. Emphasis mine.
India is a huge country with over 20 (not exactly sure) vernaculars. The official language varies from state to state. Although Hindi is considered the national language, not all people from all states speak Hindi.
From my research, I've found out that Hindi is, in fact, an official language, not the national language of India. English and Hindi are the two official languages of the country. Each state then has an additional official language of their own.
For example, here's a quote from division bench of Chief Justice S.J. Mukhopadhaya and justice A.S. Dave.
“Normally, in India, majority of the people have accepted Hindi as a national language and many people speak Hindi and write in Devanagari script but there is nothing on record to suggest that any provision has been made or order issued declaring Hindi as a national language of the country.”