I lived in the UK for a few years before moving to the US. Originally, I am from a country within Eastern Europe where English is not the first language. My mother tongue is very different from English (the structure of grammar and everything is very different), but I actually like English better now. I was born, raised, lived my life and did my education up to college in my first language, which is quite difference from English in many ways. Did my PhD in a European country where English was the work language, but not recreational. Then moved to the UK, and eventually US. Speaking foreign languages was not the norm in my family of origin back in Eastern Europe - actually I am the first, and I also have a cousin who immigrated to the US. Both of us learned everything on our own, via our experiences - foreigns languages were never spoken or exercised in my family of origin. But my parents did pay and encourage classes for me to learn some basics during elementary, middle and high school.
I definitely learned the basics of the English language in the classes in my home country, especially during high school. But learned to use it really in different countries in Europe, and eventually here in the US. All as an adult. But whatever extra sophistication I've picked up and practice now is the result of my individual exploration, I think. I think it it reflects my standards, who I am and how I like to do things. Some say we cannot learn / change effectively as adults - not my experience