OK, issue solved. Re-installing didn’t help. In fact, I realized only now that the Customize pages did not work either. Anyway, when I checked the console output again I got suspicious by the very first error message saying “Language code must have format …”. I checked the site language under Settings and it said @@LOCALE@@. I turned it into US English et voilà, everything runs just fine.
I thought you’d be interested to know, although obviously the entire thing had nothing to do with TablePress (a really great plugin, btw).
A thousand thanks for helping!
Frank