The effects of just absorbing what's around you diminishes at the C2 level. From my experience a huge effort must be made to improve beyond that, e.g. pronuncia

The effects of just absorbing what's around you diminishes at the C2 level. From my experience a huge effort must be made to improve beyond that, e.g. pronunciation won't improve without focused effort - you need a tutor or youtube videos on the topic. Still, great improvements can be made in niche areas - know you are traveling to Scotland for holiday? Watch video or two about the accent differences, few movies and you understand 95 % in no time.