There are different fluencies, all context dependent. A woodsman who knows all about kindling and flint would be bemused in an office environment where KPIs and

There are different fluencies, all context dependent. A woodsman who knows all about kindling and flint would be bemused in an office environment where KPIs and stakeholder deliverables are core terms. In a programming environment they'd be utterly lost regarding the detail, even if they grasp basics like who's in charge. Or a chemistry lab, a surgical theatre, etc. This is why there are courses in "business" versions of languages, for example. So someone can be functionally fluent in the contexts they typically encounter, while being non-fluent outside them. I doubt any native speaker can be fully fluent in all possible contexts.