How Can I Improve Understanding?
I think I'm able to read very well in english. Now i can read a article on BBC or New York Times and I find just 5-10 words I don't know.
Unfortunately I'm no able to speak but especially to understand in english.
I'm linstening to VOA (they speak slowly and use a little vocabulary) and I understand just 80% when they read news and 50% when they read stories. If I try to watch movies or tv programmes I understand few things but adding subtitles I can understand everything.
Clearly there is a big gap between reading and speaking.
Can anyone give any suggests to plug this gap?

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while reading, keep the thesaurus (better than a dictionary) open on your computer (found in word edit tools) or Wikipedia open. These tools will give you meanings quickly.

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You can read subtitles first and then watch the movie. 
Anyways, if you keep on watching, you will get better. Sometimes it looks like that learning of language has some kind of threshold, so understanding will get better once you get a lot listening practice.

For the beginning, you can choose materials on your profession or another field of your activity - that'd be easier. For instance, lectures. Movies are more complicated because of vocabulary and characters' accents.

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The problem is quite simple,you need to practice a lot! Understanding English is the matter of experience and using it with natives as often as it is possible!