Colleges in Delhi

No, not at all. You can communicate in which ever language you feel comfortable in. Things are pretty flexible and relaxed in DU. The 'medium of teaching' is both English and Hindi. For example, students of English (H) will obviously be taught in English but there is no hard and fast rule there too. I have seen many teachers constantly shifting between English and Hindi while delivering lectures. Nobody is going to point fingers at you for speaking any language other than English. College is very different from school. In an English medium school, there is often a compulsion to speak strictly in English. Nobody cares in college, to be honest. You are free to be, just be. When we say that the 'medium of teaching' of an institution is English, we mean that English is used in lectures, examinations and else where for communication. So yes, in college, you will have to use English to write an exam ( unless you are studying a different language) only. You are free to use any other language (other than English) anywhere except for when you are giving an exam.