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")?
According to Etymonline the term kitsch is a German word which entered the English language in the '20s:
1926, from German kitsch, literally "gaudy, trash," from dialectal kitschen "to smear." Earlier as a German word in English.
What we English people call ugliness in German art is simply the furious reaction against what Germans call süsses Kitsch, the art of the picture postcard, and of what corresponds to the royalty ballad. It has for years been their constant reproach against us that England is the great country of Kitsch. Many years ago a German who loved England only too well said to me, 'I like your English word plain; it is a word for which we have no equivalent in German, because all German women are plain.' He might well have balanced it by saying that English has no equivalent for the word Kitsch. [Edward J. Dent, "The Music of Arnold Schönberg," "The Living Age," July 9, 1921]