Practice. Practice. Practice. You will improve. Do you have people to practice with who can give you feedback?

And take a class in English writing for business. Buy an English language newspaper or magazine and read it each week.
Fix a meeting once a week with a native English speaking friend and get them to read over your written work that week and explain where your errors lie. For example, in the question above you use "Not from English speaking countries?" The correct usage is "not from an English speaking country?".

Little things like this give away your origins and so learning from these errors will help you improve.

I can help you on this. You need a good English language coach, someone who can spend time having a good conversation with you and listening to your speak and then correct you.

Through the repetition and constant practice, you will learn what works well in English speaking and grammar and then you will stutter less. One thing you can do is speak to the coach in your English and let the coach help you improve your English immediately.

I would love to speak with you about this on Skype.

Bruce