Change Language inside container

Hi @all

I have a problem which I am not able to solve and hope that someone can help me out.

I created a docker image with a complete ubuntu-mate (with gui that can be accessed via X2GO-Client).

When I build the image for ubuntu:16.04 everything works fine.
Although I can not change the language via the gui-setting (Add Language), I can successfully change the language via “sudo dpkg-reconfigure locales”. After re-login, all changed to the new language (in my case it is german).

When I build the same Dockerfile with 18:04 or 20.04, the build is fine, but when I change the language via “sudo dpkg-reconfigure locales” only the OS itself is in german, but NOT the application(s). The applications (kmymoney, gimp, libreoffice,…) are in english.

I also must say that when I build the image for ubuntu:16.04 and then inside the container I do a “do-release-upgrade” it also works fine (all the applications have the correct languages) - But building directly for 18.04 or 20.04 does not change the language for the applications.

Maybe you have a quick solution for me - If you are experienced you maybe know what to exactly how to change the language inside the container.
If not, I can provide the Dockerfile if needed

Thx in advance for your help

In the meanwhile I have a “workaround”
I created my own image from the squashfs of the ubuntu-mate.iso.
I uploaded my base image and I used my own image ramirezfx/mate:latest instead of ubuntu:latest
This works fine for me