While a lot of sources on wiktionary for instance agree that "kitsch" comes from dialectal german word "kitschen", the meaning of this word is different between wikitionary pages (in the french wiktionary, "kitschen" is said to be "pick up garbage", for instance).
Wikipedia does not mention this etymology, but refer to a book "Das Buch vom Kitsch".
So do we know where it come from and what does this "Kitschen" word really mean (if it ever existed as a base from "kitsch")?