German keyboards are usually QWERTZ keyboards, named after the first line of letters up to the first that differs from the English layout, which is QWERTY.
You can switch between these two using the key combination Alt + Shift.
This switch may be the cause of your keyboard behaving strangely - for example if you pressed the combination by accident. In this case z would be replaced by y and nearly every special character would be mapped differently. Try to switch layouts if you experience that.