Which it was refered to during the entire run of the show.
It´s a bit like “Star Wars” which would translate to “Sternenkriege” but was instead translated to “Krieg der Sterne” which means “War of the Stars”.
These people (or was it the same person?) who localized those two must have had a strong dislike for the plural form…
And I forgot to mention: The german version of the X Files also had a subtitle: Die Unheimlichen Fälle des FBI.
So in germany it was “File X: The eerie cases of the FBI”.