I am not an expert in the topic of language whether it is an Indian language or other

. Since Тояма and godzilla have initiated the discussion, I would like to clarify a few little things within my limited knowledge. However this topic is far more complicated than it appears if one considers the diversity among more than 1.25 billion people. In fact, we have a slogan for India, "Unity within diversity". Language is one of the diversities.
Unlike other countries, we do not have national language. But Hindi and English are designated central official language. Our passports contain both the languages (we do not have two passport system). Other than that we have 21 state/local languages. In addition to Hindi and English, these languages are used by respective local governments or administration for official purpose. People can choose their languages for official work according to their convenience. In fact, Assam has three local official languages, Assamese, Bodo and Bengali. But majority of the people speak and use Assamese. Bodo and Bengali are spoken and used in the Bodo and Begali dominated areas inside Assam.
In our parliament, both Hindi and English are used e.g. our current prime minister regularly gives speech in Hindi though his native language is Gujarati but not Hindi. Our finance gives speech in English. Those parliamentarians, who can speak neither Hindi nor English, can give speech in their own native languages with special permissions from the parliament.
In schools, I learned four languages, Assamese, Hindi, English and Sanskrit. I can also speak Bengali at the basic level. Except a few states in southern part of India, Hindi is language course in schools all other parts of India. Almost all educated people can speak Hindi at a decent level. And of course, all those "funny" Bollywood movies are quite popular and have quite a big influence :) at every level of the society... even in those states of South India.

The reason not to teach Hindi in those states has to do more with the political power struggle in Delhi between northern and southern lobbyists started at the beginning of our independence.
Another point is that Rajasthani is a different language than Hindi though they use the same script Devanagari. Nepal is another issue. Many people of Nepal are Hindus and can speak Hindi. But there are also other ethnic groups who mostly came from Bhutan, Tibet and China. They have their own languages and religious customs.