I’m not sure that my question is relevant. So i’m not a native speaker and my writing skills are not so good. I`m wondering whether the examiners would take marks for writing mistakes.
No. They are not marking English grammar and will try to make sense of what you are saying.
Obviously, at some point a student’s English might be so bad that their answer cannot be understood and then no marks could be awarded.
I think the commnest problem with English as a second language is that it often slows down students both when they are reading questions and writing their answers.So, try to adopt a concise style. I do not mean answering on one or two word bullet points, but keeping your sentences and paragraphs short so that you can fully explain in an efficient way.