Thanks for your comments :)

Maybe you should write in your native language, and let everyone else to learn the language. I don't like when people criticize your writing skills when it's not your native language.

Or maybe he wants the largest possible audience and the comment is aimed at getting him that.

I don't think the criticism was intended in a negative spirit. Getting a native speaker of the language to help edit your writing is a very helpful suggestion. It's a good way to improve your own language skills, while still making your writing available to other audiences. I would definitely encourage people to still publish in their native language though. As you point out, it encourages others to learn other languages and will be very helpful to your fellow countrymen.

It might not be correct English, but it's not even remotely difficult to understand what was meant. (In fact, I didn't even notice it was wrong until you pointed it out.)