image build with bodhibuilder crash near end-installation

Very similar report reported on VLC 4 years ago:
https://trac.videolan.org/vlc/ticket/7651

Similar but not identical bug #1495055 in 15.10 resulting in:
ERROR: hook /usr/share/apport/package-hooks/source_ubiquity.py crashed:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport/report.py", line 197, in _run_hook
    symb['add_info'](report, ui)
  File "/usr/share/apport/package-hooks/source_ubiquity.py", line 60, in add_info
    syslog = report['UbiquitySyslog'].decode('UTF-8')
AttributeError: 'str' object has no attribute 'decode'

while this bug in 16.04 results in:
    if 'Buffer I/O error on device' in syslog:
TypeError: a bytes-like object is required, not 'str'

Part of my add_info function as it appears on my computer:
def add_info(report, ui):
    add_installation_log(report, 'UbiquitySyslog', 'syslog')
    syslog = report['UbiquitySyslog']
    if 'Buffer I/O error on device' in syslog:
        if re.search('Attached .* CD-ROM (\w+)', syslog):
            cd_drive = re.search('Attached .* CD-ROM (\w+)', syslog).group(1)
            cd_error = re.search('Buffer I/O error on device %s' % cd_drive, syslog)
        else:
            cd_error = None

Now that I look at the end of Syslog, this is probably more relevent:
Oct 10 22:58:33 gl finish-install: Disabling CDROM entries in sources.list
Oct 10 22:58:33 gl ubiquity: sed: impossible d'ouvrir le fichier temporaire /target/etc/apt/sedP1IjGy: Permission non accordée
Oct 10 22:58:33 gl /plugininstall.py: Exception during installation:
Oct 10 22:58:33 gl /plugininstall.py: Traceback (most recent call last):
Oct 10 22:58:33 gl /plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 1778, in <module>
Oct 10 22:58:33 gl /plugininstall.py: install.run()
Oct 10 22:58:33 gl /plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 78, in wrapper
Oct 10 22:58:33 gl /plugininstall.py: func(self)
Oct 10 22:58:33 gl /plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 198, in run
Oct 10 22:58:33 gl /plugininstall.py: self.configure_locale()
Oct 10 22:58:33 gl /plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 562, in configure_locale
Oct 10 22:58:33 gl /plugininstall.py: self.run_plugin(language_plugin)
Oct 10 22:58:33 gl /plugininstall.py: File "/usr/share/ubiquity/plugininstall.py", line 547, in run_plugin
Oct 10 22:58:33 gl /plugininstall.py: "Plugin %s failed with code %s" % (plugin.NAME, ret))
Oct 10 22:58:33 gl /plugininstall.py: ubiquity.install_misc.InstallStepError: Plugin language failed with code 4
Oct 10 22:58:33 gl /plugininstall.py:
Oct 10 22:58:49 gl ubiquity: Gtk-Message: Failed to load module "overlay-scrollbar"
Oct 10 22:58:49 gl ubiquity: Gtk-Message: Failed to load module "overlay-scrollbar"

https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1579454/comments/10

Indeed I had chosen 'Install' directly in Grub (which seems to suggest that because it is not run by root, it failed to create a temporary file in /target/etc/default while installing language pack).

After trying to reboot machine to test, an error occured and system opened me a session for me
to test what was going on.

In it I just ran "$ gksudo ubiquity gtk_ui" and it worked flawlessly.
Same medium, same answers, but this time in the environment, in root mode.

Which suggests to me that the problem appears in non-english, while install from GRUB.

Lubuntu 16.10 (32&64 bits) works fine (install from grub menu).
Seems to have change quite much since 16.04.

"LXLE" is not an official Ubuntu flavor and so is not supported here.