I just added a comment here. The poster (眠りネロク) has a non-western username, which I copy-pasted into the comment (I don’t have Japanese language input ability installed on my PC).
However, I notice that doing so failed to activate the "link-to-reference" kind of behavior I've come to expect on SE, meaning that it is unlikely that the poster will know I just tried to tag him with a note.
Is this a failing with the language on SE? (Japanese is well-within the BMP.) Or did I do something wrong?
I do not consider this a duplicate of (above): the question is about using CJK characters with @, not whom can I ping (which I admit I did wrong).