As a person who does not speak English as a first language and then putting it into type to boot I can think of a million tough ones like words that have more than one meaning and different spellings but sound the same. Too, to, and two for example. 3 different spellings, 3 different meanings but when spoken there is no difference.
Luckily for me, those problems I eliminated in my youth.
Also, I grew up (and still live) in a suburb of Athens populated by thousands of US military personnel serving at an air force base a couple of miles from me (Hellenikon Air Force base, for those who may know).
So, up until the mid-90's when the base ceased operations, I had gotten to know many of these people and received a huge amount of practice.
Although a physicist by education (not occupation), my job in the early eighties required I also did two 2-year courses in London (International law and diplomacy and Contract law).
So, that helped a lot too.
You are right about the "writing" part, I did have to get the hang of that in the beginning.
I am still though, a sponge for information as you will have observed ;-)
The more I learn, the more I discover how little I know (just me plagiarizing Socrates lol!).
