I don’t think English is the common language of India
In fact it is, all the IT people here from India have to speak English here because there are literally thousands of different languages there, it’s the only way they can communicate with each other.
I actually googled this and holy cow (ha, ha that’s a coincidence) do they have a lot of languages. But English IS an official language of the Government.
Here is a bit from the wikipedia entry “languages of India”
“The Republic of India does not have a national language.[4][5] The official languages of the Union Government of Republic of India are Hindi in the Devanagari script and English,[6][7] a position supported by a High Court ruling.[4] The languages of the Eighth Schedule, which have been referred to as the national languages of India since Nehru initiated such a practice. The 1991 census recognized “1576 rationalized mother tongues” which were further grouped into language categories. The 1961 census recognized 1,652,[8] and the 2011 census recognized 1,635.[9] (SIL Ethnologue lists 415). According to Census of India of 2001, 30 languages are spoken by more than a million native speakers, 122 by more than 10,000. More than three millennia of language contact has led to significant mutual influence among the four language families in India and South Asia. Two contact languages have played an important role in the history of India: Persian and English.[10]”
Among "Educated" people it is the common language. Without English, your opportunities there are very limited.
That said, this is not about language. This is about an abusive individual teacher being allowed around children.
It is not about 'English.'