What is the name of this language authority? I researched and found "Council for German Orthography" and "Gesellschaft für deutsche Sprache" (Association for the German Language).

Duden (the standard German dictionary) is the closest I know. And they list "Aufmerksamkeitsdefizit-Hyperaktivitätsstörung" (the German word for attention deficit hyperactivity disorder) with 44 letters as the longest in the dictionary [1].

*Update:* There are also [2] and [3] but they are both not anymore part of a law (the "-gesetz" suffix in the word) or regulation (the "-verordnung" suffix in the word), respectively.

[1] https://www.duden.de/sprachwissen/sprachratgeber/Die-langste... [2] https://en.wiktionary.org/wiki/Rindfleischetikettierungs%C3%... [3] https://en.wiktionary.org/wiki/Grundst%C3%BCcksverkehrsgeneh...