Teach gnus/message about international Re: variants

* lisp/mail/mail-utils.el (mail-re-regexps): New defcustom,
contains the components used to construct 'rmail-re-abbrevs' and
'message-subject-re-regexp'.
* lisp/gnus/message.el (message-subject-re-regexp): Derive from
'mail-re-regexps'.
(message-strip-subject-re): Make the match case-insensitive.
* lisp/mail/rmail.el (rmail-re-abbrevs): Derive from
'mail-re-regexps'.  Update 'rmail-reply-regexp' when it changes.
(rmail-reply-regexp): Set to nil, 'rmail-re-abbrevs' will set
it.

* doc/emacs/rmail.texi (Rmail Reply): Describe
'mail-re-regexps'.
* doc/misc/message.texi (Message Headers): Describe
'mail-re-regexps'.

(Bug#72442)

2 files changed, 20 insertions, 1 deletions

diff --git a/doc/emacs/rmail.texi b/doc/emacs/rmail.texi
index 402386684ae..7a2ef9be16e 100644
--- a/doc/emacs/rmail.texi
+++ b/doc/emacs/rmail.texi
@@ -776,6 +776,14 @@ to.  The @samp{To} field starts out as the address of the person who
 sent the message you received, and the @samp{CC} field starts out with
 all the other recipients of that message.
 
+@vindex rmail-re-abbrevs
+@vindex rmail-reply-prefix
+@vindex mail-re-regexps
+The @samp{Subject} header field may contain one or more instances of
+@samp{Re:} or localized variants thereof.  These are removed if they
+match @code{rmail-re-abbrevs} (which is initialized from
+@code{mail-re-regexps}), and @code{rmail-reply-prefix} is prepended.
+
 @vindex mail-dont-reply-to-names
   You can exclude certain recipients from being included automatically
 in replies, using the variable @code{mail-dont-reply-to-names}.  Its
diff --git a/doc/misc/message.texi b/doc/misc/message.texi
index 48ac487088e..418eb14e042 100644
--- a/doc/misc/message.texi
+++ b/doc/misc/message.texi
@@ -1688,13 +1688,14 @@ result is inserted.
 
 @item message-subject-re-regexp
 @vindex message-subject-re-regexp
+@vindex mail-re-regexps
 @cindex Aw
 @cindex Sv
 @cindex Re
 Responses to messages have subjects that start with @samp{Re: }.  This
 is @emph{not} an abbreviation of the English word ``response'', but it
 comes from the Latin ``res'', and means ``in the matter of''.  Some
-illiterate nincompoops have failed to grasp this fact, and have
+standards-challenged companies have failed to grasp this fact, and have
 ``internationalized'' their software to use abominations like
 @samp{Aw: } (``antwort'') or @samp{Sv: } (``svar'') instead, which is
 meaningless and evil.  However, you may have to deal with users that
@@ -1726,6 +1727,16 @@ responding to a message:
        ))
 @end lisp
 
+You shouldn't need to do this, since the default value of
+@code{message-subject-re-regexp} is initialized based on
+@code{mail-re-regexps}, which covers most known cases of such
+internationalization, and is a lot easier to customize.  Customizing
+@code{mail-re-regexps} updates @code{message-subject-re-regexp} to
+match.
+
+Note that the regexp is matched case-insensitively against the
+@samp{Subject} header contents.
+
 @item message-subject-trailing-was-query
 @vindex message-subject-trailing-was-query
 @vindex message-subject-trailing-was-ask-regexp