Please first check if another issue has been opened for your problem

Versions

• OS: Ubuntu 18.04 Bionic Beaver
• Gajim version: 2018-05-18 10:35:38 +0000 ? (flatpak info doesn't tell)
• GTK version: unknown
• Python-nbxmpp version: unknown

Steps to reproduce the problem

1. Install flatpak with instructions from https://flatpak.org/setup/Ubuntu/
2. sudo flatpak install flathub org.gajim.Gajim
3. flatpak run org.gajim.Gajim

Expected behavior

Gajim starts normally

Actual behavior

% flatpak run org.gajim.Gajim

(gajim:2): Gtk-WARNING **: 09:55:11.831: Locale not supported by C library.
        Using the fallback 'C' locale.
Gtk-Message: 09:55:11.832: Failed to load module "appmenu-gtk-module"
Traceback (most recent call last):
  File "/app/bin/gajim", line 9, in <module>
    load_entry_point('gajim==1.0.2+6cdcbf1154c6', 'gui_scripts', 'gajim')()
  File "/usr/lib/python3.5/site-packages/setuptools-22.0.5-py3.5.egg/pkg_resources/__init__.py", line 542, in load_entry_point
  File "/usr/lib/python3.5/site-packages/setuptools-22.0.5-py3.5.egg/pkg_resources/__init__.py", line 2569, in load_entry_point
  File "/usr/lib/python3.5/site-packages/setuptools-22.0.5-py3.5.egg/pkg_resources/__init__.py", line 2229, in load
  File "/usr/lib/python3.5/site-packages/setuptools-22.0.5-py3.5.egg/pkg_resources/__init__.py", line 2235, in resolve
  File "/app/lib/python3.5/site-packages/gajim/gajim.py", line 55, in <module>
    from gajim.common import i18n
  File "/app/lib/python3.5/site-packages/gajim/common/i18n.py", line 52, in <module>
    locale.setlocale(locale.LC_ALL, '')
  File "/usr/lib/python3.5/locale.py", line 594, in setlocale
    return _setlocale(category, locale)
locale.Error: unsupported locale setting

I have experienced this issue on two similar systems, I think I asked in the MUC a few weeks ago.

My locales in case they matter:

% locale
LANG=en_US.UTF-8
LANGUAGE=en
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC=fi_FI.UTF-8
LC_TIME=fi_FI.UTF-8
LC_COLLATE="en_US.UTF-8"
LC_MONETARY=fi_FI.UTF-8
LC_MESSAGES="en_US.UTF-8"
LC_PAPER=fi_FI.UTF-8
LC_NAME=fi_FI.UTF-8
LC_ADDRESS=fi_FI.UTF-8
LC_TELEPHONE=fi_FI.UTF-8
LC_MEASUREMENT=fi_FI.UTF-8
LC_IDENTIFICATION=fi_FI.UTF-8
LC_ALL=

I haven't experienced this issue with any other flatpaks.