Halloween wasn’t popular in Germany until the early 90s. These days, however, shop windows are filled with plastic merchandise many weeks before. Carving pumpkins has become more and more popular, but Halloween is not an official German holiday.

Some people celebrate it, some don’t and I strongly doubt the term Jack O´Lantern would mean a lot to people.
http://www.uni-protokolle.de/nachrichten/id/78875/.
Halloween, it seems, is one of the American imports Germany is very torn about. There are those that celebrate it welcomingly – and according to a press release published by the University of Dortmund, the way those people celebrate Halloween comes across as more American than the way the holiday gets celebrated in the States – and there are critical voices condemning it as a purely commercial import of US culture signifying cultural imperialism.
http://idw-online.de/pages/de/news232717
Some of the latter take equivocal comfort in the fact that the ritual originated in Europe thousands of years ago. Based on the Celtic Samhain which originally used to be a ritual expressing gratitude for an abundant harvest, it was brought to the US by Irish immigrants in the mid 19th century. The Celtic calendar consisted of two seasons only and the festivities celebrated the point when summer turned into winter, so Halloween sounds more like a mixture of Thanksgiving and New Year´s, adopted and modified by the Catholic Church. Since there is a substantial amount of cultural studies research, I selected one article about Dr. Gunther Hirschfelder, from the Cultural Studies Department of the Universität Bonn, who wonders whether Halloween is an anthropological attempt at filling a cultural gap, due to a lack of significant traditions and religious rituals in Germany
http://www.uni-protokolle.de/nachrichten/id/78875/.
Also, here is a little clip about a popular Halloween Festival at Burg Frankenstein in Darmstadt:

Have fun watching!