Salam!
Some of the most important mistakes made in English are those due to the interference of French or Arabic. The interference of French is not a problem of pupils only but teachers as well.
If you take Book Four, File Four, you’ll find:
The season that I like the most is …
Correct:
The season that I like most is ….
Other mistakes many of us still make are:
Incorrect
All what I want to say is……
Correct:
All that I want to say is….
Incorrect
His parents don’t want. (Ses parents ne veulent pas.)
Correct:
1-For a usual refusal:
His parents don’t let him…
2- For a specific moment in the future:
His parents won’t let him…
or:
His parents don’t want him to….
Incorrect:
The green is my best colour.
Correct:
Green is my best colour.
Incorrect:
We should inform the responsibles.
Correct:
We should inform officials.
*A typical mistake still made by some teachers:
Incorrect:
A: Thank you.
B: Never mind.
Correct:
A: Thank you.
B: Not at all. / Forget it. / Don’t mention it. / You’re welcome…etc.
And another important problem is the misuse of ‘for’ and ‘to’ in many contexts. I’m personally suffering from this problem.
I would like colleagues to add any useful remarks about any mistake they may have noticed or will notice, however small they may seem.
Thanks for your attention.
Salam!