Ever since T66795 was fixed, now the "FROM" field of emails that a user sends to you using Special:EmailUser is alwys the same; in case of Wikimedia wikis, it is "{{SITENAME}}" <wiki@wikimedia.org>.
This is not ideal because it does not inform the user that the email is actually sent on behalf of another user. Instead, the FROM address should read: "{{SITENAME}} on behalf of $1" <wiki@wikimedia.org> where $1 is the username of the original sender.
I don't see anything I18n related here hence removing that tag.
Currently this is:
From: MediaWiki <wiki@wikimedia.org> Reply-to: AKlapper <a@b.c> To: Malyacko <x@y.z>
I only added it because we would end up introducing/modifying some i18n messages. But I guess you are correct.
Currently this is:
From: MediaWiki <wiki@wikimedia.org> Reply-to: AKlapper <a@b.c> To: Malyacko <x@y.z>
And it should be:
From: "MediaWiki on behalf of AKlapper" <wiki@wikimedia.org> Reply-to: AKlapper <a@b.c> To: Malyacko <x@y.z>