“The People’s Collection, Wales” is a fascinating online collection of items from museums, archives, libraries, and individuals in the Principality. A Christmas postcard from “Jack” of the 38th (Welsh) Division to “Edie” was part of an exhibition commemorating the Welsh experience in the First World War, a project led by the National Library of Wales. Perhaps, slightly surprisingly, the card is dated December 1918, reminding us that many troops were stuck in France for some time after the Armistice.
There’s more information on this, and the role of music in the much earlier Christmas truce in this video.