Your comments

I agree with yllen.

Good question :-)

But if notification template contain only one translation or requester(s) and watcher(s) have same language, an unique mail could be send.

Remi,
Just to custom completely our notifications.
If you want to keep this signature, leave "hide option" to users.
I know this is a hot topic : http://forum.glpi-project.org/viewtopic.php?id=30808.