I grew up bilingually with German and Russian. In school I we also had a “bilingual” English programme (meaning I had 1 more English lesson per week and that one of the secondary subjects like social studies, geography and history were taught in English each year; this was from 7th till 11th grade) and had the privilege of going on a language trip to the UK and having a tutor when I was young. My parents also had me go to a Russian Saturday school from the age of six to ~13, after which I again had the privilege of of a tutor but this time in Russian literature (mostly Pushkin)
Countless hours of YouTube, TV shows and films, videogames (+ voice chat), books and talking a lot to a trilingual friend of mine (he grew up with English, Russian and German) also helped me reach a pretty good lvl (I’d say C1+, although I haven’t taken any exams to test that yet) and I am planning on taking the Cambridge C2 Proficiency example some time in the future (in terms of preparations I am currently only reading novels like Sherlock Holmes or the Mars Trilogy from Kim Stanley Robinson. I hope to ramp it up by quite a bit though)
I am a bit embarrassed that my English is better than my Russian in terms of word pool and reading/writing skills. I speak Russian more fluently but am hoping to remedy the rest by getting into more serious Russian literature after I’m done with the Cambridge exam, maybe visiting family a bit more often, watching films/TV shows, texting and maybe calling others etc.