In Japanese, it is appropriate, when replying to a person, to include an honorific suffix.
@Atmark-chan suggested in https://www.mediawiki.org/wiki/Topic:Vvzrgsaz3p0y1pcg (← read that thread) that the Reply tool's pinging/mentioning feature should automagically insert this honorific.
"Ideally, It'll be nicer to insert the honorific (e.g., "さん" ("-san") in Japanese) and ":" after the username defaultly, just like "Atmark-chanさん:". I think It'll be good to make a message (e.g., $1さん:) and replace $1 with the username."
The message string for localizing the @ symbol could be used if a prefix were wanted. Could we have a localizable suffix as well? It might need to be gender-sensitive, and it should be possible to remove or edit it.