Fairycakes
Susie
I do wish people would pronounce “harassment” the British way rather the American way.
And I wish people would pronounce Schedule the English way, and not the American 
The French way you mean?
As for the question in title. As so often, it just depends. If it is a question of 'class' or regional accent, or genuine mistake, then it is rude to correct in most cases. This especially so if you know that this person is not an English native speaker. Same for grammar btw (and this on Internet Forums!). Just rude and in fact, ignorant.
One positive way to 'correct' is to re-use the word correctly in your reply, and hope it may be picked up.
Of course if someone is trying to learn the language and has asked to be corrected, as they wish to improve, then it is a different matter.