[Main_]

I actually had the opposite experience. Whereby, I as a non-native english speaker was surprised at the level of english of born and bred english speakers. It was disastrous at times.

Most did not go over a single sentence without using auto-correct or other tools. I've seen some copy text from the internet and put it through an article spinner, then paste it to their assignments. Not just because of laziness or the desire to cheat, but because they couldn't spell or form appropriate sentences.

[Main_]

Additionally, just because your english isn't so good doesn't mean you don't know the subject you are writing about. Unless your thesis is about English Literature, then I agree with the article.

I had a colleague who could barely write anything, but he was so outstanding in Math, that the professor asked him politely not to attend the classes anymore. His thesis was impossible to read but he still got the best marks.

Your intelligence and abilities to understand and master a subject have nothing to do with how well you write/speak.

It is however crucial to learn to write and speak properly in the longterm, especially if you decide to work/live in that country.

[tnzn]

There's still a strong myth that there is a causal effect between how well you can write, and how well you can think, conduct a logical reasoning or w/e... And of course most people who say that believe to know better than linguists/psychology researchers on the matter.