Mother Language?

It's International Mother Language Day and once again I am confused. I was born in Patna where five languages/dialects were spoken at home: English, Bengali, Hindi, Bhojpuri and Magadhi. I spent my first seven years in New Delhi where I first learned Hindi and then picked up a smattering of Bengali, Punjabi and English. In Pune, my Anglo-Indian school made it compulsory to learn the Queen's English and the local language, Marathi. My brother and I started speaking to each other only in English. Through my college years in Mumbai, I picked up the local Mumbaiyya Hindi (much to my parents' dismay) and a few Arabic words from my Gulfie pals. Through journalism, I developed a liking for Urdu, Marathi, Tamil and Persian, while I wrote English. I married a Gujarati, moved to Vadodara, and learned the differences between Gujarati, Kathiawadi and Kutchi dialects and became a student of Ashwini Milind Pradhan to learn German. In Brisbane, I learnt a bit of Australian English and borrowed a few words from Cantonese, Mandarin, Korean, Sinhalese, Japanese, Afrikaans, Dutch, Arabic and Farsi. Back in India, I think and talk English, discuss the differences between Farsi, Urdu, Dari and Hindi with Muhammad Qasem Jami and am trying to pick up the Peshawari Pushtu dialect from my friends there. With my beloved granny-in-law, I speak Kathiawadi and with my mother, I speak English. I just realised that my supposed mother-tongue, Bengali, I haven't spoken much in all my life.