Fix printing in languages other than English

[carlobeltrame]

Fixes #4751 (comment), another regression introduced in #4559 which caused the print configurator to always use 'en' as the language for the pdf.

Also added extensive tests for the print config repairing, since this is already the second bug which would have been caught if I had created these earlier.

[BacLuc]

Else it looks good.
Thank you for the tests

[github-actions]

⛔ Feature branch deployment currently inactive.

If the PR is still open, you can add the deploy! label to this PR to trigger a feature branch deployment.

[usu]

On the PR deployment, layout #2 prints in English, even if the config contains German (see screenshot). Not sure, if this is related to the comment of @BacLuc or whether this is another issue.

[carlobeltrame]

On the PR deployment, layout #2 prints in English, even if the config contains German (see screenshot). Not sure, if this is related to the comment of @BacLuc or whether this is another issue.

Nice catch. VueI18n's native locale fallbacking (which simplifies de-CH-scout to de-CH and de, before falling back to our specified fallback language of en) was not working in client print on deployments. It was a similar problem as #3068, but more subtle because generally translations worked, but not always in the right locale. Fixed in 2ad05d5.

[manuelmeister]

Looks good by reading