German keyboards are usually QWERTZ keyboards, named after the first row of letters to the first, which differs from the English layout, which is called QWERTY.
You can switch between these two using the key combination Alt + Shift.
This switch can be the cause of your keyboard behaving strangely - for example, if you pressed the combination by mistake. In this case, z would be replaced by y and almost all special characters would be mapped differently. Try to change the layout if you notice this.