It is not enough that you know how to speak English; what is important is you know how to write effectively to communicate with your peers, lecturers, professional colleagues, and employers. I have an American colleague who demonstrated that written English should really be studied even by the native English speakers.
This colleague of mine replied to an email message regarding his employer's request for submission of his credentials: transcript of records and certificates of past employments. His message said, "Iam wait for my peso check to go throw for my transcripe I have my work COE letter allready. Want the check go throw I will have transcripe."
Can you try to interpret what he wants? I can, but the way he writes it is not correct. It is generally expected that a native English speaker have good literacy skills that can transfer into various work contexts, but it is not always the case. There is really a need, especially for him, to learn written communication
Effective written correspondence yields results because it conveyes a clear and unambiguous message to the reader and produces goodwill in that reader.