अच्छा सवाल है, हम ऐसा बोलते हैं - अंग्रेजी उसकी मातृभाषा है. सहज रूप से/साधारणतया ऐसा ही कहा सुना जाता है. in informal commmunication, we may ask, what is language of your family? or which region do you belong to? or what language do you speak?. In daily life ( for Indians) I haven't ever asked anyone or heard anyone directly asking me what is you "native" language.