OK, I removed the emojis from this page: hidden link
and suddenly all the hidden translations below on the page appear.
(Relating to my message above, I finally managed to save the WPML editor for this page despite the disturbing error messages.)
However, in the right column (Fractional Change Agent) I changed the lingo to informal German, but it still shows the old text in formal German. I cannot make WPML show the text that is inside the WPML editor. on the published page as well So, how can this be solved?