The Viking raids into England and France are both very well known but I haven't heard much about their raids into Germany.
I've heard 2 different reasons for this;
Germany was too poor and the raiders preferred the richer west frankia and England.
The German way of raising troops still relied on armed freemen and peasants and so could muster defenses much faster and could repulse raiders.
I'm not sure which is closer to the truth or maybe Germany faced just as many raids as France and England and We're just subject to the Ango-French bias of medieval history.
While there will always more to be said, I summarized and discussed some possible answers before in: Why didn't the Vikings invade Germany?
whether......We're just subject to the Ango-French bias of medieval history.
As I explained before in the linked thread, this is partly valid in the sense of the extant contemporary written accounts - in Northern Germany like Germany, there was not so many religious institutions with the monks/ scribes who recorded the raids of the Norsemen at least in the 9th century after their annexation with the kingdom of the Franks.
On the other hand, German historiography has in fact accumulated fair amount of the solid research on the Vikings' activity in Frankish Kingdom, including now Germany.
These three are just a tip of the iceberg of such scholarship (if someone asks the recommended basic books on the Vikings in German, I can recommend some more easily).