I wish I could have sent this wikipedia entry to Mark Twain. It would have been a fine addition to his "museum". I'm sure he would have been thrilled to hear about it:
https://en.wikipedia.org/wiki/Rinderkennzeichnungs-_und_Rind...
The currently longest word in the Duden is Aufmerksamkeitsdefizit-Hyperaktivitätsstörung (ADHS, German for ADHD).