I've never done it before, but I decided to help out an author who's native language was not English.
I enjoyed the story, but the grammar and spelling left a lot to be desired.
The story itself got a few comments. Some were the usual "good story, more please." Others were "I can barely read this."
I could follow along, but even I had to admit the grammar and spelling errors were detracting from the overall story.
So I offered to help.