Wrong Day Name on my Page

I’m having a strange situation on my page, first of all, you might have a strange layout before hitting “shift+f5” then, the start is correct..

You see “Mittwoch” as the day (which is today – Wednesday) then you might click on the 7th

Now it shows Freitag (Friday) It should say Samstag ( Saturday ) and below in the date-line it’s correct (“Sa” above the 7)


Can you help me?