This patch shortens the additional output generated when displaying a message with PGP signatures and/or encryption. Translated versions of Mutt will probably not work with that patch (because gettext() won't find the original string it expects). Also S/MIME and all else still has the old messages (I don't use that).
The idea is by sec@42.org, I've just adapted it to version 1.5.9 of mutt.