This is the kind of sentiment I had when people ask me about 日本語 regarding: “do Japanese people memorize all 50000+ Kanji?” I’m like “NO” since they don’t know all characters as only a small percentage of that is taught & used, around 2136. Although, some people learn jargon catered to specific fields (science, medicine) leading to them knowing 3000+ Kanji.
The estimated count for the “number of words” in English is 1,000,000 but that’s not an exact answer. The thing is, how many words is a native English speaker expected to know & understand? How much vocab do they teach students at school (from spelling to grammar)? After learning the alphabet, what types of words are taught across schools in the Anglosphere to kids?
For perspective, kids in Japan only learn 80 Kanji in their first year (mainly common & easy ones: 犬、校、九、女、男、名、森、右 to list a few) but the number expands through their years. I mean, something “similar” exists in English with spelling being taught at schools (teachers give a list of words to memorize spelling followed by a spelling test later).
The vocab lists expand from elementary to high school with difficult words (there’s a difference in difficulty with trying to spell a word like “animal” to “conscientious”). It’s like how a Japanese kid knows how to handwrite 海外 but has a hard time on trying to understand 傭兵 (ようへい) since 傭 is a harder Kanji to write in comparison to 海.
Outside of hearing brand new slang for the first time, t’s pretty rare for me to come across an English word I don’t already know. But if I were to read a dictionary cover-to-cover I would certainly find some. But those would be extremely rare and esoteric words, if I don’t know them it’s because I’ve never seen anyone use them.
People don’t learn their native language by memorizing a dictionary. They learn it from being immersed in it their whole lives. When hearing a unknown word for the first time, if you understood every other word in the sentence then nine times out of ten you’ll be able to infer the missing word from context.
Maybe sometimes you occasionally come across a rare word that’s not obvious from context, but the longer you’ve been using a language the rarer this is - you get better at picking things up from context and it gets rarer how often you even encounter unknown words to begin with.
There will always be words out there you’ve never heard, but if they’re rare enough for you to have never encountered them when using your native language your whole life, they might be rare enough for you to never encounter them in the future - unless you just read a dictionary to find them.