This is the question asked by many language learners. When will I be able to talk fluently and to understand native speakers? Of, course the answer isn’t easy.
There are two types of vocabulary: active and passive. Active vocabulary is a range of words you use in a conversation or in writing. Passive vocabulary is a range of words you can recognize reading a text or listening to the speaker. The average active vocabulary of English native speaker is about 20.000 words and there are about 40.000 words in his passive vocabulary.
I think that I reached the level of knowing about 6.000-7.000 words passively and about 3.000 words actively. I know it because I use “Learning with Texts” – program which is very helpful in reading texts. There are some statistics about the number of words used in texts which I put into the program. The numbers looks frustrating.
Every thousand words to learn is really hard work for me. Luckily 3.000 words provides coverage for around 95% of common English texts. Some of this few percent may not be possible to recognize from context, but these rare words very often are crucial in the texts I read or listen to.
I read somewhere that about 5.000 actively known words allow one to speak the language quite fluently. When I reach this level (if this happens) I will be able to recognize probably about 10.000 words.
However the way to native fluency looks infinite.