There are many languages that are within the country, some that are well known include tamil, telegu, marathi, malayam, hindi (urdu), arabic (some people speak it in india), south indian.......there are too many, over 400!!
Apart from Hindi and English, there are 17 officially recognized languages in India. In addition there are many other regional languages spoken by large sections of population bu not recognized officially - one such language that comes to my mind is Konkani. In addition there are many dialects of theses language. I do not have count of these but I believe these run into hundreds.
The purpose for learning any language, national, regional, or foreign is same - to be able to communicate. We learn languages so that we can understand others, and others can understand them. Apart from direct communication with people, language knowledge of any language enables us to also learn from the written and other similar sources of information in that language.
It is a good idea for an Indian to learn another regional language to communicate with people who cannot speak any other language well. But every Indian learning all other Indian language will be wasteful and perhaps impossible for most of the people. If we insist that an Indian must learn all the 17 regional languages before learning English, the net result will be that most of the Indians will be cut off from rest of the world.
Before I end there is a small proble for you to think about. If four Indians from different regions of the country, but all of them knowing all the 17 regional language, in which language will they talk?
While there are many language spoken in India, there are over 400 indigenous languages of Nigeria. What that says about us as a people is that we are divided, separate, and living apart from one another.
Speaking another language bridges those divides and unites us not in just language but in culture and understanding. Isn't oppression and war based on divisions and not understanding each other?