Describe the bug:

XFCE VNC does not get fully localized into French (first image below) after installing the locale and setting the environment variables.

Expected behaviour:

The XFCE installed applications (using thunar as an example) to appear in French (second image below).

Steps to reproduce the issue:
In a docker file

FROM mltooling/ml-workspace-minimal:0.12.1
RUN \
    apt-get update && \
    apt-get install -y locales && \
    sed -i -e 's/# fr_FR.UTF-8 UTF-8/fr_FR.UTF-8 UTF-8/' /etc/locale.gen && \
    locale-gen && \
    dpkg-reconfigure --frontend=noninteractive locales && \
    clean-layer.sh
ENV LANG=fr_FR.UTF-8 LANGUAGE=fr_FR.UTF-8 LC_ALL=fr_FR.UTF-8

Build: sudo docker build -t mltest
Run: sudo docker run --rm -p 8080:8080 mltest
Navigate to desktop gui

Technical details:

• Workspace version: 0.12.1 (base)
• Docker versionL: 20.10.0
• Host Machine OS (Windows/Linux/Mac): Linux
• Command used to start the workspace : sudo docker run --rm -p 8080:8080 mltest
• Browser (Chrome/Firefox/Safari): Firefox

Possible Fix:
I don't know :(

Additional context:
I've looked at and extended just an xfce specific image here and was able to get the UI to fully appear in French (see second image below). That image is based on ubuntu:16.04.

I would instead expect something like