Dear Prince,

Bachelor in Commerce (B.Com) degree is pursued by those who have passed their 12th from Commerce or Science. If you have done your 12th in Hindi medium you would be looking for B.Com in Hindi. Well don't worry you can do that. Colleges offer B.Com in Hindi and also the books are also available in Hindi. If you are not comfortable with English you can go for it.

Hello,
It depends on the college you are talking about. Mostly it is going to be a mixture of Hindi and English or any other regional language if the state speaks languages other than Hindi. In posh colleges too, you can expect a mix of languages while being taught. Anyhow, it will definitely not be a problem because you wil get used to the language it is taught in a short time.
Good Luck!