Sentence:  Ramanujan has also argued that many Hindu men have both a <WSD>mother tongue</WSD> (the everyday language, such as Tamil, spoken by women downstairs, in the back,  in the kitchen) and a father tongue (once Sanskrit, more recently English, the literary lingua franca spoken—or at least discussed—by men in the front rooms). 
Meaning of the word marked with <WSD> tags:  The language one first learned; the language one grew up with; one's native language.