Take me as English learner for example. I would say I was only able to understand everyday English without too much of a hassle, after I acquired like around 10k words, which as I just checked had a coverage about 98%+.
Noted, it is still NOT enough, actually far from enough. Right now I believe I master around 15k to 20k words, by various estimates, and navigating English on the internet is like a charm, very little context switch in between with my native language.
Still, reading literature is huge undertake for me. I would still need to pardon myself about every once a page that if I stumped upon certain unknown words/phrases and can't move on before fully understands it, my pleasure of reading would be ruined. Such comprise frustrates me still, to this day. On the other hand, I will never have a second thoughts reading most cryptic novel in my own language, understanding might still be a challenge, but unlikely due to my insufficient vocabulary.