UnicodeEncodeError while command line upgrade from 12.04 to 12.10

This is on a german Ubuntu 12.04 installation, so that these envvars are set like this:

LC_MESSAGES=de_DE.UTF-8
LC_COLLATE=de_DE.UTF-8
LANG=de_DE.UTF-8
LC_CTYPE=de_DE.UTF-8

I did the following:

sudo do-release-upgrade -d

When the upgrade told me how long the upgrade will eventually take, I pressed d for details.
This triggers a traceback with the following error:

UnicodeEncodeError: 'ascii' codec can't encode character u'\xbb' in position 1: ordinal not in range(128)