I'm given a lot of different types of documents and presentations to review from my Japanese client. Some speak/write near perfect English, some don't. How I approach these reviews is providing "alternative wording" or "suggested edits", allowing them to pick and choose the ones they like. This way, they can take some of my suggestions, all of them, or edit my suggestions a bit, and everyone is happy and saves face. By the way, I was lost in Tokyo once near my clients office one morning and I could find not find one person (young students, university ages, or businessman) that could speak English and direct me to the right place. Some had a look of horror that I was about to approach them and speak English. So, it's not just Thailand with low proficiency and we can't call the Japanese lazy.