Time and again I've seen plenty of mid career professionals (and some big bosses for that matter) making scores of grammatical and spelling mistakes in their writing. I think e-mail has a lot to do with it. That's not all they make obvious language mistakes when they talk. People talk about these mistakes behind the person's back on most occasions.
Unfortunately many of the bosses refuse to confront these mistakes promptly. They feel it's best to let it go. On most occasions they feel the recipient might feel intimidated.
This doesn't help the individual at all. In fact at a later stage in their careers it will become a hindrance for career progression.
Fundamentally, younger generations who study in their mother tongue and learn English as a secondary language believe mastery of the language is way beyond them. However with concentrated effort one can master the language over a period of 3- 5 years (up to a respectable level in the corporate world).
Trust me, the typical class room learning can do very little to bring a person up to speed with the language usage. (Those of you who believe sending some one for a English course would solve the problem, you are dead wrong!) Its all about application and application in real life situations where you need to rectify yourself.
So what stops people from learning the language properly during their adulthood?
From a receipient's point of view they need to do two things.
a) They need to accept the fact that they can make mistakes when it comes to the language and more importantly it is ok to make mistakes as long as you don't repeat it.
b) They (the recipient) need to proactively indicate to the boss that they seek feedback and they appreciate the same. (You need to have the urgency to up your game!)
From the boss's point of view they need to commit the necessary time and energy on constant basis to give feedback. And when they do they should focus on the issue and not on the person while ensuring it is one to one.
So next time around when one of your subordinates make a mistake, ensure you give prompt feedback. If you haven't done it before, talk to them prior to giving feedback and tell them why you are doing it.