The German term Doppeldenken translates literally to double thinking. It was used - and possibly also introduced - in 1889 by the German psychiatrist Emil Kraepelin (1856-1926) to denote * audible thinking, or what the German psychiatrist August Cramer (1860-1912) had previously designated as * Gedankenlautwerden.
References
Kraepelin, E. (1889). Psychiatrie. Ein kurzes Lehrbuch für Studirende und Ärzte. Dritte, vielfach umgearbeitete Auflage. Leipzig: Verlag von Johann Ambrosius Barth.
Dictionary of Hallucinations. J.D. Blom. 2010.