> Would you say a native English speaker doesn't know the word "they're" if they keep spelling it "their" even if they use it correctly 100% of the time?
Bad example, but to roll with it: In that case I would say they don't know it properly, since it is apparent, that in their mind there is no difference between "their" and "they're" or even "they are".
> How does this opinion hold up if you consider that spelling wasn't standardized three centuries ago. Did no one know any English words until spelling got standardized in the 1800s? Do illiterate native speakers not truly know any words? Do children not know words?
I am basing my personal definition of when I consider a word "learned" on reality, not on some "what if". If I had to map that idea of no spelling standardization to Chinese characters, then it would mean, that characters don't have standardized lines/components/parts. If there was no standard, then I guess I would consider this kind of making up how to write it on the fly sufficient for having learned a word. Thankfully there is standardization, so that is not a reality we live in.
Since I strive to not be an illiterate, I do not count being illiterate as having learned a word.
> EDIT: And in any case, 10 new vocabulary words per day is extremely easy. In my experience having studied two foreign languages at the university level, that's pretty much the bare minimum expected to get an B in class.
That depends very much on the language and course, but if it is your major, then sure, such a time commitment seems reasonable, since it is the thing you are doing. If your major is anything else and you just take an additional language course, where I come from you have once or twice a week that course. Then maybe 1 or 2 weeks you finish one chapter of a course book, which might have 20 new words, so that makes 20 words in 1-2 weeks, not in 2 days.
Typically for Mandarin the speed will also be slower than other easier to learn languages. For example at school I almost never had to learn vocabulary in English or Spanish. I just saw the words and memorized them somehow. Usage in class and often their sound and structure was sufficient , and always had good grades, often very good grades in those languages and always had good grades, often very good grades in those languages.
It doesn't work like that with Chinese characters. You are not gonna learn them (including writing them) by just looking at them a few times, unless you got an extraordinary visual, almost photographic memory. I consider myself already to have a pretty good visual memory, but still I need to put in the time and effort, and 20 words a day is way out of my league. But then again it was already cleared up in another comment, that the OP cuts out writing entirely. That's definitely a choice one can make and explains how 20 newly added words (I would still debate that that's "learned") make any sense.