How do I change the default language in Collabora?

When installing Nextcloud with Collabora you have the option to choose dictionaries that can be used in Collabora. The problem is that when you create a new Collabora document, the default language of the document is always ‘German’, independent of what languages you chose.

For a long time the solution to this issue has been changing the template files in the core/templates/filetemplates folder as is explained in this topic:

But this solution is not working anymore, as you can see in that topic. So I open a new topic to raise this issue again, in search for a new solution. Does anyone have ideas?

All the best,

P.S I installed Collabora & Nextcloud using this playbook: https://github.com/ReinerNippes/nextcloud_on_docker . Those all update to the latest versions (NC16.0.1).

The issue is also raised in the Nextcloud repo: