I'm not a native English speaker either, I've been in the US for 15 years now. What worked very well (from my point of view) for me, was binge watching America

I'm not a native English speaker either, I've been in the US for 15 years now. What worked very well (from my point of view) for me, was binge watching American movies/shows. I would watch maybe 3 hours each day before going to bed, and I feel like my brain worked a lot on that while I was asleep. As for what seems to be your introvert temperament, not sure what would work best. Maybe finding groups around you that do something you like.