Sigh.
Your argument is incoherent so it's not clear if you're arguing for a common language other than English or no common language at all.
If it's the first one, that's a road that will lead to certain disaster. Requiring knowledge of a specific Indian language will automatically grant native speakers of that language advantage over other Indians. If tomorrow Gujarati or Bengali was chosen as the "national" language and every book was published in Gujarati, every movie and show was dubbed in it, every textbook was rewritten in it, every government form was written in it, wouldn't Gujaratis have an advantage over everyone else? Wouldn't everyone else implicitly become second class citizens?
That's not even hypothetical. This experiment of forcing a "national" language on population that never spoke it or understood has been tried before. It was a spectacular failure. Bangla speakers in East Pakistan didn't want to speak Urdu and didn't want to be treated as second class citizens because they couldn't. So they seceded. East Pakistan doesn't exist anymore.
No doubt you're thinking "no, not Gujarati/Bengali. Let's choose Hindi as the national language". Now understand this -> Hindi is a foreign language to me, though I am Indian. I studied it for 10 years so I'm reasonably fluent in it, but it is still a foreign language, as foreign as English. For that reason, states such as Tamil Nadu and Kerala will not accept the imposition of Hindi. This battle started in the 60s and continues today.
Of course, you might be arguing for no common language at all. Let's root out English and in it's place let's have ... nothing. I'm not sure what that would buy us, but sure.
English is a foreign language, but it is the only language is foreign to all Indians. That is why it is fair for it to remain an official language of the Indian Union.
FYI, you and I wouldn't be having this conversation if we didn't have English as common language.