I depends on where in Germany you are staying. If you're going to Bavaria, better prepare for some tough cold nights! - 20°C can happen, at night even less !(though most of the time in the south you have about -5 to -15 °C at day, in the north 5 to -10°C) If you're staying in the north you might manage with a dress and tights, but buy some thick wool tights! Do you have a decent winter coat and nice winter boots? You will definately need something with thick soles.
Layering is a great option so you don't have to buy too many pieces you can't use back at home.
Layering is a great option so you don't have to buy too many pieces you can't use back at home.