I want to make a comment for this answer but because one user has a Chinese character as its user name, I failed to refer it in the comment. Shortly speaking, how to trigger the auto-completion (aka IntelliSense in Visual Studio) for a non-latin user name?
On a qwerty keyboard, you need to copy at least the first character from the name and paste it after
@ in order to initiate the auto-completion:
If selection from the available comments is difficult (due to hyperlinks), click on the user name and select from the user profile.