From time to time (e.g. just now) I'm getting comments submitted that are written in what looks like Chinese. I routinely reject these submissions because I have no idea what they are saying, and for all I know could be some sort of attack.
Logically, if the reader is in fact commenting on a post, then he or she must have been able to read the post in the first place, which implies knowledge of the English language, so I do consider it reasonable to expect comments be written in English as well.
Nothing against Chinese or any other language - I wish I could learn them all.