Which traditional celebrations do you have in Germany?

See a translation

That's strongly dependant on the region. Most state wide holydays are linked to religion (christianity), some to political events (Tag der deutschen Einheit, reunification of germany). There are no huge celebrations on this day though.
Many people celebrate christmas and easter with their families to some extent, but that's about it.

Outside of those, you obviously got the Oktoberfest, and Fasching/Karneval.
Fasching/Karneval differs extremely depending on the region you're in. While it is a huge deal in western Germany with millions of participants and a whole week ofpeople dressing up and drinking publicly (mostly in cologne/Düsseldorf/Aachen and their surroundings).Northern Germany is comparably quiet, besides one single day. In the south, they have a completely different approach, with various local traditions.