My list's moderator interface and plain format digests have garbled non-ascii. Change English charset to utf-8.
Mailman's character set for English is us-ascii. This causes non-ascii characters in posts and message headers and footers and other places to be replaced by question marks and/or numeric HTML entities in various contexts in the web interface and in plain format digests. This can be avoided by changing Mailman's character set for English to UTF-8. This has not been done in the GNU Mailman distribution for mainly superstitious reasons, but it is believed to be safe.
For Mailman 2.1, this is done by placing the line
add_language('en', 'English (USA)', 'utf-8', 'ltr')
in mm_cfg.py and restarting Mailman.
For Mailman 3, this is done by adding the settings
[language.en] charset: utf-8
to mailman.cfg and restarting Mailman core.
The one known downside of doing this is that Python's email library which is used by Mailman will base64 encode charset=utf-8 message bodies which makes the raw message body impossible to read by eye or search with simple tools like grep.