There’s some confusion about which message this is exactly…
This is the current default text template for account_silenced (it’s been like this for YEARS):
You have been silenced from the forum until %{silenced_till}.
Reason - %{reason}
and this is the email you get when silenced via this dialog:
@codergautam the message you’re looking at is silenced_by_staff which looks to be the default and is sent when… I’m not exactly sure but probably triggered by an automated process, not the above manual interaction