I was born in one, lived long in a second and now am home in a third country.
In all three languages I feel confident, can tell jokes, understand and have tested level C2 (https://www.efset.org/cefr/).
Still, every once in a while, I "have this feeling" my proficiency is subpar. Still I learn new expressions and grammar twists that I was now aware about before.
What helps me getting more certain and better in the word craft of the local language is asking locals to correct me and ask them to explain words and constructs that seem strange or unknown to me.
In all three languages I feel confident, can tell jokes, understand and have tested level C2 (https://www.efset.org/cefr/).
Still, every once in a while, I "have this feeling" my proficiency is subpar. Still I learn new expressions and grammar twists that I was now aware about before.
What helps me getting more certain and better in the word craft of the local language is asking locals to correct me and ask them to explain words and constructs that seem strange or unknown to me.