This story is a tricky one. A client speaks English as his second language, and he does so impeccably. His English is precise, because he knows the rules of grammar better than most people who speak and write English as their first language.
Knowing all the rules makes him confident about correcting the expression of others (including me), and he points out wording that is ‘wrong’. Here’s the tricky part: our English is ever evolving, so what is ‘wrong’ for one person can be exactly ‘right’ for another person.
In other words, English can be a grey area. To find your shade of grey, you need to step outside your own knowledge of the language. Be keenly aware of how your work colleagues use English. What is acceptable, and what grates? What is changing? And how does time and place affect what’s said?
You may find the greys of English allow you to grow as a writer. They will certainly allow you to craft text that reaches more people.