Recently, I've started studying 21.000 word list from the internet. I cannot learn anything from that because when I translate to my native I don't understand the meanings. So that's where my question comes from. If I learn 9000-10000 words will I be able to speak like a native speaker and understand every topic (I will learn the most important ones)?
How many words you know is pretty much irrelevant (once you get beyond a certain number). You need to understand how to put them together and how to pronounce them in order to "speak like a native speaker". Get that in place, and then you can start expanding your vocabulary.
There is an article on The Economist's website (which I quote in part) that gives some interesting figures:
Several years ago we mentioned TestYourVocab.com here on the blog. Not long ago, the site reached its two millionth test result, and so the researchers have put together some data:
- Most adult native test-takers range from 20,000–35,000 words
- Average native test-takers of age 8 already know 10,000 words
- Average native test-takers of age 4 already know 5,000 words
- Adult native test-takers learn almost 1 new word a day until middle age
- Adult test-taker vocabulary growth basically stops at middle age
- The most common vocabulary size for foreign test-takers is 4,500 words
- Foreign test-takers tend to reach over 10,000 words by living abroad
- Foreign test-takers learn 2.5 new words a day while living in an English-speaking country
As you can see, 10,000 words will get you to the level of an average 8-year old. You will need between 20,000-35,000 words to sound like an adult native speaker. However, I am a little dubious about these figures. An adult should be able to make much better use of a 10,000 word vocabulary than any 8-year old, since his thought patterns ought to be more sophisticated.
"It's not the years, honey. It's the mileage." -- Indiana Jones
I agree with Mick that sounding like a native speaker has very little to do with the number of words you know. Just because you can give me the book definitions of (for example) "dirty", "grimy", and "squalid" doesn't mean you can use each in the correct context.
Personally, I think fluency is more about phrases than words, and more about idiom than vocabulary. For example, do you know what I mean when I say
My soda has gone flat
She flatly refused my proposal
She has a nice singing voice, but she keeps going flat.
Some English words have as many as a dozen different meanings, depending on context. A fluent speaker would know most or all of them, or at least be able to take a good guess.