The problem:
“3 days ago” should translate to “vor 3 Tagen” in German, while “3 days” translates to “3 Tage”. #21408 describes that django always translated to “Tage”, even when the dative “Tagen” was correct. The same applies to months (“Monate”/“Monaten”) and years (“Jahre”/“Jahren”).

The solution:
Let `timesince` caller provide the string dict to use for the time-related strings.