I think your English is pretty good, actually. I mean, yes you're obviously not a native speaker but I feel like the vast majority of the time I understand what you're trying to get across.

That said: yes, there have been ESL winners. Most of the ones I remember won because they had a good/interesting character idea and managed to get it across. Some of that's a bit of luck of the person running the contest liking the kind of idea you have -- I remember Aarn picked Nabburak to win one time, and the role idea didn't really appeal to me but Aarn thought it was awesome and it was his call to make.

Quality of writing obviously can help and hurt you a lot, but I think a strong, original character idea can trump that. Reading roles/comments of characters with PBFs up can help you with the originality angle.