Travelling advice in December

Berlin is a super choice! I've been there sooo many times!

But. what are you actually interested in seein?
Berlin is all about shopping and historical buildings, monuments, memorials and nightlife.
I don't think the parks are worth much in the winter.
I'd recommend min. 5 days in Berlin.

I really like Neuschwanstein too. (its a castle on a mountaintop). It's pretty far away from berlin though. But dude, if there's snow, you totally have to go take a look. I've been there in Summer, but the winter pics of it are amazing!

I personally really enjoy cities like Prague and Vienna.

So I am looking places like art galleries, museum, and live music (preferably jazz and classical) ?

Nightlife in Berlin does not hurt either, I have heard Techno music is big there?

I guess Berlin would also be a good place to start, because of its historical significance?

Castle in Potsdam would be an additional bonus...

The question I have is should I visit Germany in christmas? Because there is no much going on in Christmas in the UK, so I am not sure whether most of places will be shut in Germany.

Re:Koneko Lora I guess I have to add Dresden to my next to do list

Thanks so much guys. I really appreciate your advices

Dresden has alot beautiful old galleries and museum too like
also the christmas market is wonderful, the big "Striezelmarkt"

but its up to you, I think winter is good when its not too cold and rainy

During Christmas everything's decorated and I mean.. Christmas markets attract tourist from other countries every year, never heard of other markets like this outside Germany.
I don't think art galleries, museums, etc depend on the season so winter, around Christmas time, should be fine. Everything's closed for two and a half days (usually 24th starting at midday/1PM and both 25th and 26th are official holidays) but shortly before Christmas should be fine.
I've only been to Berlin once, can't say a lot about the city but Hamburg, Munich, and nearly every city should be fine about the cultural institutions.