Well, for many of us who started school in the 50s and 60s, we were were much home with the English language. In fact, because academically (reading and writing) we were forced to use English, we were/are more inclined to use and think in English. Heck, maybe I even speak English in my dreams. It was not our mother tongue but it was our intellectual medium of expression. Here’s is Bill Bryson’s The Mother Tongue: English and How It Got That Way. You can download the audiobook here.
The later Rev. Father Dapoz was once quoted that he even dreamt in the Kadazan language, such was he at home among the Kadazan-Dusun community and their spoken tongue. That, I can attest to: I remember he used to interject during conversations with the 30 and 40-year old Kadazan-Dusuns and teach them the meanings of obscure Kadazan words.