I’m from Québec and fluent in both French and English (spoken and written).
I went through an exclusively French curriculum (with interspersed English and Spanish classes in both high school and cegep). University was mostly in English.
At home, we spoke mostly in 2 other languages (still speak well enough but unfortunately I never learned to write in) with both sides of the family, with English as a go between when needed.
I was nowhere any good in any of my language classes, frequently zeroes (out of 10 or 100) in written quizzes and tests (I tended to write phonetically). I don’t know how I (barely) passed without ever failing a single class 🤣. I am better now, probably out of lifelong practice.
I was way better, if not excellent, in mathematics, physics, chemistry and most sciences in general.
What probably helped was my continuous daily immersion in both French and English with friends, family, coworkers, colleagues, clients, neighbors and also through shows, movies, music, books, journals, contracts and various projects.
Although, nowadays, I personnaly feel (false impression perhaps) like my English vocabulary is vastly larger than my French one.