Why can some people speak in a second or foreign language with such accuracy and fluency?
If you want to have and possess such good things as accuracy and fluency, you should for example read massively in that L2.
Because we can use and employ some of the words that we input and intake by means of for example reading massively.
Reading what? Literature, non-fiction also is convenient, etc. Always those books should be in accordance to human dignity: we feed ourselves from what we read.
What amount of words can I use? Fewer than the words I intake, definitely.
The more words I intake through reading the more words I will be capable of using. Also we should consider that that reading books should take rather long in time.
Summing up: the more I read, the more words I will be capable of using. Have a nice day! / Photo from: Boeing 747