I'm not really sure how to answer that.
You can do an Aviation English course but I am not sure whether they are ICAO accredited or not.
That is not to say that they are not, I am new to the whole ICAO environment and the test I am using here is part of a larger research project.
If you send a PM to Planeenglish, she would be much more qualified to answer that question for you.
I hope this is a help.
Farrell