Mailman can't decode some non-english characters during arch command

Symptoms

During the mailman "arch" command, the following error is returned:

File "/usr/local/cpanel/3rdparty/mailman/bin/arch", line 190, in main
archiver.processUnixMailbox(fp, start, end)
File "/usr/local/cpanel/3rdparty/mailman/Mailman/Archiver/pipermail.py", line 587, 
in processUnixMailbox
a = self._makeArticle(m, self.sequence)
File "/usr/local/cpanel/3rdparty/mailman/Mailman/Archiver/HyperArch.py", line 685, 
in _makeArticle
mlist=self.maillist)
File "/usr/local/cpanel/3rdparty/mailman/Mailman/Archiver/HyperArch.py", line 321, 
in __init__
self.body = [l.decode() + "\n" if isinstance(l, bytes) else l + "\n" for l in body.splitlines()]

File "/usr/local/cpanel/3rdparty/mailman/Mailman/Archiver/HyperArch.py", line 321, 
in <listcomp>
self.body = [l.decode() + "\n" if isinstance(l, bytes) else l + "\n" for l in 
body.splitlines()]
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x93 in position 26: 
invalid start byte

Description

Since Mailman upgraded from Python 2 to Python 3, some characters in the archives cannot be decoded. Python 3 prefers UTF-8 to decode, which might not be able to read some characters from the previous version.

We've opened an internal case for our development team to investigate this further. For reference, the case number is CPANEL-47173. Follow this article to receive an email notification when a solution is published in the product. 

Workaround

None available.