[thaumasiotes]

> I have learned a host of them to intermediate level, and then run aground on getting to advanced, which I think of as the ability to express yourself colloquially and elegantly on any random topic.

If this is your standard, then to within rounding error, 0% of people have reached an "advanced" level in their own native language(s). Elegance is difficult.

(Though some people do seem to believe in a similar standard. My sister grew up in the United States, in an exclusively English-speaking household, and graduated from the University of Pennsylvania. She joined the state department and took their English ability test (I assume for fun). She scored less than fluent - according to the rubric, not qualified to talk to Anglophone college graduates.

I can attest personally that college graduates don't seem to mind if you, as a foreigner, don't know the specialized vocabulary they learned in college.)

[shanusmagnus]

I think you and I have a different notion of what "elegance" means. To me, it's not that high a bar. A native speaker who reads for fun and cares about self-expression generally achieves it. It does, however, prove a high bar for a non-native speaker in my experience.