Hi @nilsgildo, this seems to be an issue of a third party developer, so unfortunately we're unfamiliar with this, but we'll do our best to help.
Like the users in the GitHub repo mentioned, could you try running the following in the container?
In order to verify it is fixed, restart the container and see if it works.
If it does not fix the issue, try this:
install_packages fontconfig ttf-dejavu
Please let us know if you're still finding the issue.