"One does not eat horses."
Translation:Man spiser ikke heste.
Add some onion and... I almost walked right into that one. No, of course not! That would be wrong! You shouldn't eat horses!
To whoever wrote this task: You probably had some without knowing, too. When it's all blended, you don't even notice.
Man spiser ikke heste sounds more descriptive to me, whereas En spiser ikke heste is more a rule or a commandment. Anyway, that is my gut feeling (which is heavily influenced by my native Dutch).
Just as in German, 'man' (not 'mand') is the acceptable way to use a subjuct when you have no idea who it is, or you don't want to say it, maybe avoiding admitting it's you.
The other option is passive voice, I.e. "Horses aren't eaten": "Heste SpiseS ikke". Danish uses passive quite often, maybe because it is such an easy construction, switching the r to an s, but it can sometimes can cause confusion.
From my experience, using "én" is old-fashioned, but probably still common in some dialects, but not seen in written language, except in a quote, of course. My husband and I are watching an old TV comedy series from 1970+ "Huset på Christianshavn" (no subtitles, unfortunately), where at least one character, "Meyer", uses én instead of "jeg". I think my Danish svigerfar, en bonde fra Randersegn, born around 1910, also used én this way.