But those last .1 % are not very useful anyway if you're not living abroad. You want to be able to communicate fluently and not make noticeable mistakes, but it's not necessary to seem like a native speaker. Unless you want to become a spy maybe.
Conversational literacy is a huge step on its own.
I have found that English is a bit weird in that you need obsessively high absorption of like, culture, to execute well, so it’s easier to spot non-native speakers.
This applies to every language out there, English is certainly not an exception in this aspect.
I'd think that English is not unique there.
To speak Chinese at the level of an educated native, I'd say you have learn not only the language, but also the country's history, and have some familiarity with canonical Chinese texts such as the "Four Books and Five Classics" (Confucius, Mencius, etc.), "The Dream of the Red Chamber", etc., to understand idioms such as "四面楚歌" (four sides of Chu song = facing insurmountable difficulty, defeat [1]).
As another example, Hong Kong has its own lingo (a variety of Cantonese) that evolves so rapidly that HK people that have been abroad a few years tell me that they note that the language has evolved and shifted when they come back.
I'm fairly certain that it is easy to spot non-native speakers in many languages, maybe even easier than in English.
And I'm afraid that last 0.1% of aquisition is pretty much impossible to obtain deliberately unless you abandon your native language. Even your English, whilst technicaly good, has a couple of flags.