
No record of this quotation appears to exist in German.
In The World Crisis, Vol I: 1911-1914 https://books.google.com/books?id=6l6Fgnz8fXIC&lpg=PP1&pg=PA96#v=onepage&q&f=false (originally published in 1923), Winston Churchill asserted that during the July Crisis, German shipping magnate and diplomat Albert Ballin told him that Bismarck had said to him, "that one day the great European War would come out of some damned foolish thing in the Balkans" a year before his death.
The full quote above appears in "European Diary" by Andrei Navrozov, in Chronicles Vol. 32 (2008) as a comment during the Congress of Berlin in 1878. "European Diary" is a series of excerpts from Navrozov's unpublished (as of 2017) novel in English, Earthly Love: A Day in the Life of a Hypocrite.
Disputed