Comment 20 for bug 1256588

Ok. I tried the following.

I got ubiquity_2.15.9_powerpc.deb ubiquity-frontend-debconf_2.15.9_powerpc.deb ubiquity-frontend-gtk_2.15.9_powerpc.deb ubiquity-ubuntu-artwork_2.15.9_all.deb from http://ftp.tu-chemnitz.de/pub/linux/ubuntu-ports/pool/main/u/ubiquity/ and installed them forcibly, after installing the dependencies python3-pyicu and python3-oauthlib. Here is the output:

# dpkg --force-all -i ubiquity_2.15.9_powerpc.deb ubiquity-frontend-debconf_2.15.9_powerpc.deb ubiquity-frontend-gtk_2.15.9_powerpc.deb ubiquity-ubuntu-artwork_2.15.9_all.deb
dpkg: warning: downgrading ubiquity from 2.17.10 to 2.15.9
(Reading database ... 119659 files and directories currently installed.)
Preparing to unpack ubiquity_2.15.9_powerpc.deb ...
Unpacking ubiquity (2.15.9) over (2.17.10) ...
dpkg: warning: downgrading ubiquity-frontend-debconf from 2.17.10 to 2.15.9
Preparing to unpack ubiquity-frontend-debconf_2.15.9_powerpc.deb ...
Unpacking ubiquity-frontend-debconf (2.15.9) over (2.17.10) ...
dpkg: warning: downgrading ubiquity-frontend-gtk from 2.17.10 to 2.15.9
Preparing to unpack ubiquity-frontend-gtk_2.15.9_powerpc.deb ...
Unpacking ubiquity-frontend-gtk (2.15.9) over (2.17.10) ...
dpkg: warning: downgrading ubiquity-ubuntu-artwork from 2.17.10 to 2.15.9
Preparing to unpack ubiquity-ubuntu-artwork_2.15.9_all.deb ...
Unpacking ubiquity-ubuntu-artwork (2.15.9) over (2.17.10) ...
Setting up ubiquity-ubuntu-artwork (2.15.9) ...
dpkg: ubiquity: dependency problems, but configuring anyway as you requested:
 ubiquity depends on python3-pyicu (>= 1.0); however:
  Package python3-pyicu is not installed.
 ubiquity depends on reiserfsprogs; however:
  Package reiserfsprogs is not installed.

Setting up ubiquity (2.15.9) ...
locale: Cannot set LC_ALL to default locale: No such file or directory
dpkg: ubiquity-frontend-debconf: dependency problems, but configuring anyway as you requested:
 ubiquity-frontend-debconf depends on ubiquity (= 2.15.9).

Setting up ubiquity-frontend-debconf (2.15.9) ...
dpkg: ubiquity-frontend-gtk: dependency problems, but configuring anyway as you requested:
 ubiquity-frontend-gtk depends on ubiquity (= 2.15.9).
 ubiquity-frontend-gtk depends on gir1.2-gnomekeyring-1.0; however:
  Package gir1.2-gnomekeyring-1.0 is not installed.
 ubiquity-frontend-gtk depends on python3-oauthlib; however:
  Package python3-oauthlib is not installed.

Setting up ubiquity-frontend-gtk (2.15.9) ...
Processing triggers for desktop-file-utils (0.22-1ubuntu1) ...
Processing triggers for mime-support (3.54ubuntu1) ...
Processing triggers for man-db (2.6.6-1) ...
locale: Cannot set LC_ALL to default locale: No such file or directory
Processing triggers for ureadahead (0.100.0-16) ...
Processing triggers for hicolor-icon-theme (0.13-1) ...
root@lubuntu:/home/lubuntu/Downloads# dpkg --force-all -i ubiquity_2.15.9_powerpc.deb ubiquity-frontend-debconf_2.15.9_powerpc.deb ubiquity-frontend-gtk_2.15.9_powerpc.deb ubiquity-ubuntu-artwork_2.15.9_all.deb
dpkg: warning: downgrading ubiquity from 2.17.10 to 2.15.9
(Reading database ... 119662 files and directories currently installed.)
Preparing to unpack ubiquity_2.15.9_powerpc.deb ...
Unpacking ubiquity (2.15.9) over (2.17.10) ...
dpkg: warning: downgrading ubiquity-frontend-debconf from 2.17.10 to 2.15.9
Preparing to unpack ubiquity-frontend-debconf_2.15.9_powerpc.deb ...
Unpacking ubiquity-frontend-debconf (2.15.9) over (2.17.10) ...
dpkg: warning: downgrading ubiquity-frontend-gtk from 2.17.10 to 2.15.9
Preparing to unpack ubiquity-frontend-gtk_2.15.9_powerpc.deb ...
Unpacking ubiquity-frontend-gtk (2.15.9) over (2.17.10) ...
dpkg: warning: downgrading ubiquity-ubuntu-artwork from 2.17.10 to 2.15.9
Preparing to unpack ubiquity-ubuntu-artwork_2.15.9_all.deb ...
Unpacking ubiquity-ubuntu-artwork (2.15.9) over (2.17.10) ...
Setting up ubiquity-ubuntu-artwork (2.15.9) ...
dpkg: ubiquity: dependency problems, but configuring anyway as you requested:
 ubiquity depends on reiserfsprogs; however:
  Package reiserfsprogs is not installed.

Setting up ubiquity (2.15.9) ...
locale: Cannot set LC_ALL to default locale: No such file or directory
dpkg: ubiquity-frontend-debconf: dependency problems, but configuring anyway as you requested:
 ubiquity-frontend-debconf depends on ubiquity (= 2.15.9).

Setting up ubiquity-frontend-debconf (2.15.9) ...
dpkg: ubiquity-frontend-gtk: dependency problems, but configuring anyway as you requested:
 ubiquity-frontend-gtk depends on ubiquity (= 2.15.9).
 ubiquity-frontend-gtk depends on gir1.2-gnomekeyring-1.0; however:
  Package gir1.2-gnomekeyring-1.0 is not installed.
 ubiquity-frontend-gtk depends on python3-oauthlib; however:
  Package python3-oauthlib is not installed.

Setting up ubiquity-frontend-gtk (2.15.9) ...
Processing triggers for desktop-file-utils (0.22-1ubuntu1) ...
Processing triggers for mime-support (3.54ubuntu1) ...
Processing triggers for man-db (2.6.6-1) ...
locale: Cannot set LC_ALL to default locale: No such file or directory
Processing triggers for ureadahead (0.100.0-16) ...
Processing triggers for hicolor-icon-theme (0.13-1) ...

The error still occurred. I'm not sure if that was the right method, but it looks like 2.15.9 is installed:

# dpkg -l "*ubiquity*"
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-==============-============-============-=================================
ii ubiquity 2.15.9 powerpc Ubuntu live CD installer
un ubiquity-artwo <none> <none> (no description available)
ii ubiquity-caspe 1.339 all Configuration hooks for live inst
un ubiquity-front <none> <none> (no descblription available)
ii ubiquity-front 2.15.9 powerpc debconf frontend for the Ubiquity
ii ubiquity-front 2.15.9 powerpc GTK+ frontend for Ubiquity live i
un ubiquity-slide <none> <none> (no description available)
ii ubiquity-slide 80 all Ubiquity slideshow for Lubuntu
ii ubiquity-ubunt 2.15.9 all Ubuntu artwork for Ubiquity live
un ubiquity-ubunt <none> <none> (no description available)

This is unfamiliar territory so I probably missed something important.