Xubuntu 18.04.1 LTS install fails in debconf.py

[Eric Urban]

When trying to install via LiveUSB ubiquity never launches.

/var/log/installer/debug contains the following

Ubiquity 18.04.14.6
/usr/lib/ubiquity/ubiquity/frontend/gtk_ui.py:54: PyGIWarning: Gtk was imported without specifying a version first. Use gi.require_version('Gtk', '3.0') before import to ensure that the right version gets loaded.
  from gi.repository import Gtk, Gdk, GObject, GLib, Atk, Gio
debconf (developer): <-- VERSION 2
debconf (developer): --> 0 2.0
debconf (developer): <-- CAPB
debconf (developer): --> 0 multiselect escape
debconf (developer): <-- GET ubiquity/custom_title_text
debconf (developer): --> 10 ubiquity/custom_title_text doesn't exist
debconf (developer): <-- GET oem-config/enable
debconf (developer): --> 10 oem-config/enable doesn't exist
debconf (developer): <-- GET ubiquity/automation_failure_command
debconf (developer): --> 10 ubiquity/automation_failure_command doesn't exist
debconf (developer): <-- GET ubiquity/show_shutdown_button
debconf (developer): --> 10 ubiquity/show_shutdown_button doesn't exist
debconf (developer): <-- GET ubiquity/hide_slideshow
debconf (developer): --> 10 ubiquity/hide_slideshow doesn't exist
debconf (developer): <-- GET debian-installer/locale
debconf (developer): --> 10 debian-installer/locale doesn't exist
Exception in GTK frontend (invoking crash handler):
Traceback (most recent call last):
  File "/usr/lib/ubiquity/bin/ubiquity", line 655, in <module>
    main(oem_config)
  File "/usr/lib/ubiquity/bin/ubiquity", line 639, in main
    install(args[0], query=options.query)
  File "/usr/lib/ubiquity/bin/ubiquity", line 270, in install
    wizard = ui.Wizard(distro)
  File "/usr/lib/ubiquity/ubiquity/frontend/gtk_ui.py", line 274, in __init__
    self.locale = i18n.reset_locale(self)
  File "/usr/lib/ubiquity/ubiquity/i18n.py", line 35, in reset_locale
    di_locale = frontend.db.get('debian-installer/locale')
  File "/usr/lib/python3/dist-packages/debconf.py", line 83, in <lambda>
    lambda *args, **kw: self.command(command, *args, **kw))
  File "/usr/lib/python3/dist-packages/debconf.py", line 119, in command
    raise DebconfError(status, data)
debconf.DebconfError: (10, "debian-installer/locale doesn't exist")

Traceback (most recent call last):
  File "/usr/lib/ubiquity/bin/ubiquity", line 655, in <module>
    main(oem_config)
  File "/usr/lib/ubiquity/bin/ubiquity", line 639, in main
    install(args[0], query=options.query)
  File "/usr/lib/ubiquity/bin/ubiquity", line 270, in install
    wizard = ui.Wizard(distro)
  File "/usr/lib/ubiquity/ubiquity/frontend/gtk_ui.py", line 274, in __init__
    self.locale = i18n.reset_locale(self)
  File "/usr/lib/ubiquity/ubiquity/i18n.py", line 35, in reset_locale
    di_locale = frontend.db.get('debian-installer/locale')
  File "/usr/lib/python3/dist-packages/debconf.py", line 83, in <lambda>
    lambda *args, **kw: self.command(command, *args, **kw))
  File "/usr/lib/python3/dist-packages/debconf.py", line 119, in command
    raise DebconfError(status, data)
debconf.DebconfError: (10, "debian-installer/locale doesn't exist")

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity (not installed)
ProcVersionSignature: Ubuntu 4.15.0-29.31-generic 4.15.18
Uname: Linux 4.15.0-29-generic x86_64
ApportVersion: 2.20.9-0ubuntu7
Architecture: amd64
CasperVersion: 1.394
CurrentDesktop: XFCE
Date: Fri Oct 26 18:14:55 2018
InstallCmdLine: initrd=/casper/initrd file=/cdrom/preseed/xubuntu.seed boot=casper only-ubiquity quiet splash --- BOOT_IMAGE=/casper/vmlinuz
LiveMediaBuild: Xubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=C.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)