The archives at lists.gnu.org can be downloaded in mbox format. Examining these, both attachments of your mails are encoded in iso-8859-1. So it's either the mailing list or gnus.
Just as a test a hopefully utf8 encoded file is attached. Felix
\header{ title = "Lettre à Élise" } \markup { }
_______________________________________________ bug-lilypond mailing list bug-lilypond@gnu.org https://lists.gnu.org/mailman/listinfo/bug-lilypond