If English language skills are weak and you're going to take TOEFL coaching, will it be possible to tackle the GMAT after the TOEFL? After all, the only purpose of the coaching is to improve your English.
Next, 'poor English skills' will mean different things to different people, and I'm not sure what you mean.
It's hard to judge just from the wording of the query, but your English seems ok, though there are some problems of course (For instance, you should have written "BY then", not "UNTIL then".)
Again, I'm not sure what your friend meant by "deep knowledge of English". Whatever he meant, the GMAT does not need a deep knowledge of anything! It's an exam for people who want to become managers, and it tests reasoning skills (It's not an exam for people who want to become English language professors!)
Re "ability to understand is much better than to speak or write":
The GMAT does not test your ability to speak. It hardly tests your ability to write (with a little prep you will be able to write the essay EASILY).
The GMAT definitely tests your ability to understand. This means the ability to understand written material of university textbook level. If that is a problem, you will need to prepare -- study, practise, improve. Almost everyone needs to prepare: some need to put in more work and some less.
On whether you can get to your target score by September: depends on your current level and on how much time you can devote to preparation and on how you prepare.
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