1 ikiwiki version 3.20170111 on Debian 4.9.30-2+deb9u3 with locale fr_FR.UTF-8
3 UTF-8 characters like û and é get turned into the unicode replacement character (xFFFD) in "Last edited" date, "published" date and in the calendar plugin content.
4 User provided content (page title or content) isn't affected.
6 Examples here : https://blog.chat-porc.eu/archives/2017/
8 Having strftime_utf8 systematically return POSIX::strftime(@_) resolves the bug, but I'm pretty sure it's not a proper fix.