If you can pronounce these words, then you probably can say that you know German:
Fußbodenschleifmaschinenverleih (31 letters) (meaning: shop that lends floor sanding machines)
Donaudampfschiffahrtsgesellschaftskapitän (41 letters) (meaning: Danube steamship company captain)
Rindfleischetikettierungsüberwachungsaufgabenübertragungs- –gesetz (63 letters) (meaning: law for the delegation of monitoring beef labelling) – this is the the longest “authentic” word in the German language.
Donaudampfschiffahrtselektrizitätenhauptbetriebswerkbauunter- -beamtengesellschaft (79 letters) (meaning: Association for subordinate officials of the head office management of the Danube steamboat electrical services) – this word appears in the Guinness book of records. It allegedly was a suborganization of the Donaudampfschiffahrtsgesellschaft in pre-war Vienna (Austria) a shipping company for transporting passengers and cargo on the Danube. The DDSG still exists today in the form of the now private companies DDSG-Blue Danube Schiffahrt GmbH (passenger transport) and the DDSG-Cargo GmbH. However, there is no evidence that the suborganization ever existed.