The great thing about English is that it is so flexible that you don't need to 'master' it.
Take for example chinese, they don't use past tense in their language, they establish that it is something in the past, and then talk present tense.
Some do this with English and say "Yesterday I go to the store and I buy some eggs."
Even though English doesn't work like this, if we know that's their style, we accept it and understand it.
So it is a very flexible language.
Extremely flexible with pronunciation as well. There are 44 phonemes in English (individual sounds) and we use these to pronounce our words. Spanish has 26, so most latinos mispronounce our words, but because pronunciation is so flexible, we just get used to it and accept it.
We even accept Germans using V instead of W, like "ven-eh-va" for 'whenever'.
The thing that makes American English harder than British is that Americans speak 'implied' english a lot of the time. They will remove words. Like 'get drunk again?' could mean 'do you want to get drunk again?' or 'did you get drunk again?'
All depends on the context. A woman looking ill, 'get drunk again?' would mean one thing, but if a girl said 'I could do with a few beers like last night if you want,' and you replied, 'get drunk again?' it would mean 'want to get drunk again?'
I agree with that our language is highly flexible in daily use.
But the sentence structure and usage is a indicator of educational level, social status and intelligence. Not TRYING to master it or improve says to people you are OK with your station.
Speech writers, politicians, poets, song and fiction writers strive in using the right words, and think a great deal about it.
"De Doo do do De Da da da"- Sting
'Yesterday, December 7, 1941 a date that will live in history'
this was changed to-
'Yesterday December 7, 1941 a date that will live in infamy'
"The difference of one word can mean the difference between a lighting bug and lightning" Mark Twain