[Closed] German translation doesn't show up in the frontend even it's available in the backend

Background of the issue:
I am trying to connect 47 original English blog posts with manually translated German blog posts. We were not satisfied with some of the German translations, so we put the German version into trash and translated it again with ATE.
The translation shows up in the backend (both in the blog post overview and in ATE), but not in the frontend.

Here are two samples to investigate:
hidden link (English) and hidden link (German -> Page not found).

Another example:
hidden link and hidden link. If you need access to the site, let me know.

Symptoms:
The German translation is available in the backend but does not show up in the frontend. Instead, I get a 'Page not found' error.

Questions:
Why does the German translation not appear in the frontend even though it is available in the backend?
How can I resolve the 'Page not found' error for the German translation?