I wrote something about that in another thread...
Although I was supposed to be a Muslim by birth, I grew up with Christians. I even attended Christian religion. So I hesitate to say that Christianity is a foreign religion to me.
My mother as well as her parents were "modern" people. I know the parents of my mother only from what she told me; I met my grandfather only on the funeral of my grandmother when I was a baby. They were both interested in progress and overcoming traditional bounds. My grandfather had been appointed by the British to "develop" Somaliland before WW2 and got an important job when Britain had decided to change this territory from the status of a protectorate to a real colony.
My mother has stepped into this, with little criticism of colonialism but rather enthusiasm for European culture and distance to Islam.
My grandparents of my father's side were caring people and convinced social democrats. They had survived Nazi Germany saying yes,yes and doing no,no as it was possible. My grandmother has never been religious in that time but later found friends among the Jehovah's Witnesses. She was impressed with the steadiness and courage they had in this time. I think she always attended their meetings but never really joined them. That was when I was searching for my own way to religion. I attended some of their meetings as well but I felt repelled by the fact that they had a preformed answer to everything and little openness to wider questions, and they told me that unless I join them, I'ld be lost. That was when I was 17 years old.
At the age of 19, I met a good Muslim who had the open mind I needed in my religious search and he also had good open-minded but well founded answers. This made me decide to keep to Islam, so that Islam is of course even less a foreign religion to me.
I recently got interest in the older religion of East Africans. It's also been a monotheistic religion. But the generations before, those who were not Muslim (from birth for many generations) have accepted Christianity maybe under force, but finally with much enthusiasm, so that there is nobody left who still practices the old religion. It's a bit a post-mortem encounter with a foreign religion, and I don't know very much so far...