I would say that fluency is not about what you can. For example, if you can understand 70% of a movie, you most probably can get the rest 30% without too much trouble, just from the context. Or, for another example, you still can be understood even if your grammar knowledge is absolutely atrocious. So, understanding or measuring are quite relative things when it comes to the language learning. For me personally, being fluent is just being confortable in a language, eg. to use a language (to speak, read, listen) for a long time without getting tired of it.

I will know I am fluent in English when I to communicate myself with a natural flow, confidence and be able to express my ideas clearly. Understand movies and understand what the people want to say including different accents.

Funny question. I have always said "I can speak Spanish." Even when I was an absolute beginner I would say that. However, now that I can actually speak some I still feel that I am am beginner because each step forwards that I take inspires me to be able to do it better and I see how far I can go :)

I'll be fluent when words will come out without lags in my speech

Being fluent in English as a second language means that I can be a creative writer or blogger and people won't be repelled by "lameness" or lack of eloquence won't be obvious. When it comes to speaking I've never met anyone who learned English well enough for being mistaken for a native speaker. Listening - when you are able to understand 99 percent of a movie and 100 percent of a documentary. IELTS test shows that I can understand 31 out of 40 tracks which enough for almost any faculty of any university. However, I strongly feel that I am not able to understand live speech. In my arrogant opinion someone is fluent when he or she can sell a used car to a native speaker :-)