A soldier to the right plays music on an old piano. He is accompanied by another soldier playing the violin. The soldiers are drinking dark beer and smoking cigars and cigarettes. The soldier on the left is holding a rag or perhaps it is an apron. It could be that he is the bartender for the group.
A huge, elaborately decorated Christmas tree looms in the corner, and the walls are festooned with evergreen branches. No doubt about it; it's a Christmas scene. These soldiers are lucky. While they are not with their families, at least they are gathered with comrades and friends around a warming stove and not freezing in the trenches.
The hand-lettered sign in the lower righthand corner of the photograph translates literally as "2nd War Christmas". It is possible that "2te Kriegs=" is an abbreviation for "2te Kriegs-Nummer," which might be German for "2nd Battalion."
(via Sunny Brook)