What I always say is that the end goal isn’t to learn a language. That’s just a starting point. The end goal is to effectively communicate with a group of people.

It goes so far beyond grammar and vocabulary. That includes accents and slang, that includes politeness and conventions, that includes history, that includes culture, that includes phrases and sayings and shorthands, that includes popular media etc. All that’s really only possible from immersing yourself in a group of people, and even then, you’re only learning that group of people, that demographics limited to location and time and age.

Hell, my friends and I reference Spongebob so often that its effectively part of our language. Memes are embedded in the way we communicate to the point where we’re speaking a different dialect than our parents.