PER, parç qe penséu qe "årstiðen" isch pü cumpeténs, es ocså parç qe ça tent el mismeu pläts es la mismă meþodă d'articülaziun qe 'n altră fonimă qi uça <en> per formar el plural.
(PER, because I think "årstiðen" looks cooler, and also because it has the same place and method of articulation as another -en-plural phoneme.)