I have been working in a foreign language environment for more than a decade. Probably still sound like a child from time to time.

For some context, my (self observed) fluency of the language is around CEFR C1 level. No issue at all in every day conversation.

Listening / reading for the most part was not a problem i.e. I'm able to understanding and critically thinking about what people are saying in real time.

Speaking was more challenging for me. It took me about three years until the first time I felt I was close to expressing myself without major pause-and looking-for-words. Now it's a lot better, I can and frequently speak in meetings with or without preparation, but my level of expression is still limited, compare to my colleagues.

I feel like speaking for business is similar to children learning any language: I listen to what other adults are saying in what context to what opponent, and I try to mimic that. After several years I got enough vocabulary to get by in day to day tasks, including meetings, writing docs, discuss code designs, etc.