Present day India is one of the most language-diverse countries in the world with 1652 languages spoken by its 1.3 billion citizens. There are five language families: Indo-Aryan, Dravidian, Sino-Tibetan, Austro-Asiatic, and Andamanese. The Indian constitution contains 18 national languages: Assamese, Bengali, Gujarati, Kannada, Hindi, Kashmiri, Konkani, Malayalam, Manipuri, Marathi, Nepali, Oriya, Punjabi, Sanskrit, Sindhi, Tamil, Telugu, Urdi, Bodo, Santali, Maithili, and Dogri. Hindi is considered the official language, but not a national language and is spoken by over half of the Indian population.
In a census taken in 2011, 121 languages and 270 mother tongues were recognized. As you can see, this figure is significantly smaller than the actual number of languages and mother tongues spoken in India. This is because the census defined a spoken form of communication as languages if and only if it is spoken by more than 10,000 Indians. This means that over 1000 of the languages spoken and used in India have less than 10,000 speakers.
Of course, all these languages did not appear suddenly, but rather came about with the presence of many foreign entities throughout India's history. In ancient India, the invasions by Persians, Alexander the Great, and Chinese Pilgrims started to diversify India's language profile. In Medieval India, the Mughals and Turkish have great impact on language. And of course, the colonization of India until 1947 by the British Empire remains one of the most significant and impactful, not only in terms of culture but linguistically by introducing and at times enforcing English as a lingua franca in India.
While English's introduction started in the 18th century as a method to make native Indian more "civilized," over the years and now post-colonization, Indians have transformed British English into Indian English, an internalized form of English that is exclusive to India. English plays many roles in India. One of the most interesting of these role is its role in India's education system. India's education system is structured in a way that there are three language formulas: a primary language (a state language), a secondary language (usually English), and a national language (Hindi).
And most higher education and post-graduate education is taught and communicated exclusively in English. Proficiency in English is often used as an indicator of class and education level. Many workplaces view fluency in English as a key hiring criteria even if the job does not necessarily require it. Additionally, prominent public figures in India talk in public (interviews, ads, etc.) a majority of the time in English. This includes actors/actresses, newscasters, and politicians. This is due to the perception of knowledge of English and elevated class. In fact, the association is so deep that lack of proficiency in English can be heavily determinate in terms of pursuit of higher education, job opportunity, and public perception.
Additionally, code-switching and code-mixing between mother tongues and English is very common in India. Often times in conversation, people will insert English words into Hindi sentences or even switch languages between dialogues. This is not due to lack of vocabulary in native languages, but rather a representation of how internalized English has become in Indian society. Evidence of this can be seen by the fact that code-switching and code-mixing is not at all random but has its own grammar rules and syntax associated with it.