Hi Leon,
Yes english is my first language. I only posed this question because i got worried when i read that someone's appliction was returned after he had submitted it with a 10-page written submission.
You do not need to show evidence of language proficiency for Sydney. All you need for Sydney is forms, mailing labels, copy of passport biodata page, and CAD drafts for thr CRF. Written submission/ielts only comes in when you're required to submit a full application to the Accra visa office. If you can do the ielts, i will advise you write the tests, this is quite important if you're really banking on full 16marks for English language, and your total score is just on the borderline. If on the other hand, you have a high total score and you'll still qualify even with 8points under language proficiency, then a written submission may be advisable. The problem is that Immigration officers aren't trained Language Proficiency Assessors and so you can find cases where a Nigerian applicant with an M.Sc from the UK is being given a score of 8, and another one with a B.Sc from Nigeria is given a full score of 16.
The good thing is though, if you do submit a written submission for the language proficiency, and the CiC official finds that the score you get for that will make you fall short of the 67points passmark, they will not automatically refuse the application, they have to notify you, and request that you provide ielts test results within a time frame, after which they will re-assess based on the ielts result, or refuse if the applicants has failed to provide the test results.