It seems that mutt is ignoring the locale setting when displaying text:

My terminals have native ISO-8859-1 (latin1) and locale is set properly.
But mails with a different character set are not converted into ISO-8859-1
when displaying. For example, UTF-8 is displayed binary and not in
ISO-8859-1. This looks like:

From: framstag@rus.uni-stuttgart.de
To: framstag@rus.uni-stuttgart.de
Subject: F*EX-upload: zzA¼A?A zz
Date: Wed, 2 Jul 2008 19:18:44 +0200 (CEST)

framstag has uploaded the file
"zzA¼A?A zz"
(2009 kB) for you.

The relevant headers of this mail are:

Subject: F*EX-upload: =?UTF-8?Q?zz=C3=A4=C3=BC=C3=9F=C2=A0zz?=
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

This mail should be displayed as:

Ulli Horlacher disait le 07/03/08 que :

recompile with +ENABLE_NLS (is it not the default ?)