Original version:
  http://www.emaillab.org/mutt/1.5.14/patch-1.5.14.tamo.pgp_charsethack.1

How to use it?

1. copy /usr/ports/mail/mutt-devel in your $HOME/ports
	$ cp -r /usr/ports/mail/mutt-devel ~/ports
2. expand the distfile and apply FreeBSD patches
	$ cd ~/ports/mutt-devel
	$ make patch
3. apply the patch
	$ cd work/mutt-1.5.16
	$ patch -p1 < /path/to/mutt-1.5.15.tamo.pgp_charsethack.1_FreeBSD.patch
4. compile the package
	$ cd ../..
	$ make build
5. install it
	($ sudo pkg_deinstall mutt-devel # if you have a previous version)
	$ sudo make install

diff -uNr mutt-1.5.15.orig/PATCHES mutt-1.5.15/PATCHES
--- mutt-1.5.15.orig/PATCHES	Sat Apr 21 16:51:27 2007
+++ mutt-1.5.15/PATCHES	Thu Apr 19 09:21:57 2007
@@ -1,3 +1,4 @@
+patch-1.5.14.tamo.pgp_charsethack.1
 vvv.quote
 patch-1.5.0.ats.date_conditional.1
 dgc.deepif.1
diff -uNr mutt-1.5.15.orig/init.h mutt-1.5.15/init.h
--- mutt-1.5.15.orig/init.h	Sat Apr 21 16:51:28 2007
+++ mutt-1.5.15/init.h	Thu Apr 19 09:21:57 2007
@@ -1405,6 +1405,17 @@
   ** settings can be overridden by use of the \fIsmime-menu\fP.
   ** (Crypto only)
   */
+  { "pgp_charsethack", DT_BOOL, R_NONE, OPTPGPCHARSETHACK, 0},
+  /*
+  ** .pp
+  ** If \fIset\fP, Mutt will assume a non-MIME PGP armored message to be in
+  ** the charset specified in \fICharset:\fP armor header (by GnuPG) or in
+  ** \fIContent-Type\fP message header (by some MUAs). You should not set
+  ** this variable, because such an armor shouldn't have charset information.
+  ** By default, Mutt assumes such messages to be in UTF-8 (see RFC2440).
+  ** You will ignore the RFC if you set this variable!
+  ** (PGP only)
+  */
   { "pgp_ignore_subkeys", DT_BOOL, R_NONE, OPTPGPIGNORESUB, 1},
   /*
   ** .pp
diff -uNr mutt-1.5.15.orig/mutt.h mutt-1.5.15/mutt.h
--- mutt-1.5.15.orig/mutt.h	Sat Apr 21 16:51:28 2007
+++ mutt-1.5.15/mutt.h	Thu Apr 19 09:21:57 2007
@@ -482,6 +482,7 @@
   OPTASKCERTLABEL,
   OPTSMIMENOSENDER,
   OPTSDEFAULTDECRYPTKEY,
+  OPTPGPCHARSETHACK,
   OPTPGPIGNORESUB,
   OPTPGPCHECKEXIT,
   OPTPGPLONGIDS,
diff -uNr mutt-1.5.15.orig/pgp.c mutt-1.5.15/pgp.c
--- mutt-1.5.15.orig/pgp.c	Sun Apr  1 23:58:57 2007
+++ mutt-1.5.15/pgp.c	Sat Apr 21 16:49:27 2007
@@ -264,6 +264,7 @@
   short maybe_goodsig = 1;
   short have_any_sigs = 0;
 
+  char *gpgcharset = NULL;
   char body_charset[STRING];
   mutt_get_body_charset (body_charset, sizeof (body_charset), m);
 
@@ -332,6 +333,8 @@
              && (mutt_strcmp ("-----END PGP SIGNATURE-----\n", buf) == 0
                  || mutt_strcmp ("-----END PGP PUBLIC KEY BLOCK-----\n",buf) == 0)))
 	  break;
+	if (mutt_strncmp ("Charset: ", buf, 9) == 0)
+	  gpgcharset = mutt_substrdup (buf + 9, NULL);
       }
 
       /* leave tmpfp open in case we still need it - but flush it! */
@@ -417,9 +420,7 @@
       }
       
       /*
-       * Now, copy cleartext to the screen.  NOTE - we expect that PGP
-       * outputs utf-8 cleartext.  This may not always be true, but it 
-       * seems to be a reasonable guess.
+       * Now, copy cleartext to the screen.
        */
 
       if(s->flags & M_DISPLAY)
@@ -442,12 +443,15 @@
       {
 	FGETCONV *fc;
 	int c;
+	char *expected_charset = ((!option (OPTPGPCHARSETHACK)) ? "utf-8" :
+				  (gpgcharset ? gpgcharset : body_charset));
 	rewind (pgpout);
 	state_set_prefix (s);
-	fc = fgetconv_open (pgpout, "utf-8", Charset, 0);
+	fc = fgetconv_open (pgpout, expected_charset, Charset, M_ICONV_HOOK_FROM);
 	while ((c = fgetconv (fc)) != EOF)
 	  state_prefix_putc (c, s);
 	fgetconv_close (&fc);
+	FREE (&gpgcharset);
       }
 
       if (s->flags & M_DISPLAY)
@@ -1422,13 +1426,11 @@
     int c;
     FGETCONV *fc;
     
-    if (flags & ENCRYPT)
-      send_charset = "us-ascii";
-    else
-      send_charset = "utf-8";
-
-    /* fromcode is assumed to be correct: we set flags to 0 */
-    fc = fgetconv_open (fp, from_charset, "utf-8", 0);
+    send_charset = option(OPTPGPCHARSETHACK) ? body_charset :
+                          ((flags & ENCRYPT) ? "us-ascii" : "utf-8");
+    fc = fgetconv_open (fp, from_charset,
+                        option(OPTPGPCHARSETHACK) ? send_charset : "utf-8",
+                        M_ICONV_HOOK_FROM);
     while ((c = fgetconv (fc)) != EOF)
       fputc (c, pgpin);