I don't know about other languages, but the French government actually does have tests of French fluency (DELF/DALF exam), which test you in a range of ways (oral comprehension - usually a radio emission, written comprehension - usually a news article, writing on a choice of subjects and speaking - presenting a view on a subject and then debating), at a variety of levels. I took one of these tests (I'm fluent, yay!), and it certainly was testing. But it seemed fair and appropriate, also seemed to correlate with my experiences speaking to French people in France.

Movies are, in my humble opinion, not the best "standard" yard stick to measure fluency. First thing is that films most often use quite limited vocabulary, and it's wildly different vocabulary than, say, found in newspapers, technical writing or in business language. Moreover films present a wide variety of communication styles. It's much easier to understand James Bond than South Park, because humour is actually quite high and demanding register of speech.

It really depends on the film though. There are family dramas I can understand 100% but I watch a movie with lawyers or science or high level government or military meetings and I'm lost.

Interesting. When watching movies in English as a native Spanish speaker it's the other way around, at least for me. It's much easier to understand a movie with plenty of scientists, intellectuals or government officials than one with average people, as those tend to use slang, colloquial expressions and Americanisms that they don't teach you in courses. In fact teenage flicks are probably the hardest genre to understand...

There's that too. And that's more evidence I'm not fluent. In English if someone uses new slang on me I understand it almost immediately from context. In my 2nd language I'm lost