I, too lived in Germany for several years. The weather is somewhat dependent upon exactly where they will be located. If they are in the far south, they will have much more snow in the mountains. But most of Germany does not experience extremes of temperature as a rule. Summers are much cooler than much of the US. 60s and 70s as I remember. Winters would hang in 30s mostly. In spite of how far north the country is located, the Gulf Stream moderates much of the climate of central Europe. It is gray a lot. It will also depend upon whether they will live "on the economy" (in an apartment or house they rent in the city in Germany) or if they will be in military housing. When I lived there (many years ago), I found that Germans kept much of their homes much cooler than what I was used to. Often they didn't heat bedrooms much. But they had those wonderful down comforters! In quarters provided by the military you can often control your temperature to some degree. We had steam heat and radiators which were first come, first serve. Meaning that since we were on the first floor, I got all the heat first and easily kept our home toasty. However, the military turned the heat on on a specific date and turned it off on a specific date. If there was an early or late cold snap, no heat! So I don't think you have to make the quilt for extreme cold. What I would do is ask them where they will be stationed exactly and then check the averages at
http://www.weatherbase.com/weather/city.php3?c=DE.