A typo that was translated in kind.

In English it says [Fir], which obviously is a typo, but in German it was translated to [Tanne] which means “fir tree”.

While the English version is close to the real thing ([Fr]) and thus could slip through if you are careful, there is no way any decent translator wouldn’t ask for confirmation when they are translating “Mon, Tue, Wed, Thu, Fir tree, Sat”