Mismatch between declared and actual encoding in mail notifications and web pages

[Johannes Rohr]

See https://lists.uferwerk.org/cgi-bin/mailman/listinfo/

I have tried to manually enforce UTF-8 by adding

```python
 add_language('en', 'English (USA)', 'utf-8', 'ltr')
 add_language('de', 'Deutsch', 'utf-8', 'ltr')
```

We see this misbehaviour since we migrated mailman from one server running Ubuntu 14.4 with mailman 1:2.1.14-3ubuntu0.4 to another server running 16.10 with mailman 1:2.1.22-1ubuntu0.1

On the old server, it worked just fine without any additional tweaking and on the new server, not tweaking seems to change anything at all.

In the mailman error log I see recurring error messages of the sort:

```
 Apr 24 15:10:19 2017 (898) list: mitglieder: can't decode "Liste f�r Mitglieder der Uferwerk e.G." as utf-8
 Apr 24 15:10:19 2017 (901) list: mitglieder: can't decode "Liste f�r Mitglieder der Uferwerk e.G." as utf-8
 Apr 24 15:10:20 2017 (901) list: mitglieder: can't decode "Liste f�r Mitglieder der Uferwerk e.G." as utf-8
```
I am not sure why these descriptions were suddenly in latin-1 but I manually converted them to utf-8 now, restarted mailman, and the situation remains unchanged: Both the overview page and the mail notifications are in latin-1 while the headers declare that they are in utf-8, which results in broken rendering of the text

[Johannes Rohr (jorohr)]

sorry, please close, I'll resubmit, because the text is incomplete in the beginning