The 29-year-old joins the Reds from 2. Bundesliga side, 1860 Munich, where he made 105 appearances in four years.
He has also had stints at Wolfsburg, FC Energie Cottbus and Alemannia Aachen and has played over 280 matches in the German second division, scoring 29 goals and recording 42 assists.
Adlung also made five appearances for German’s under-21 side as a youngster.
“I’m delighted that Daniel has signed for Adelaide and we’re looking forward to him joining our team for two seasons,” Adelaide coach Marco Kurz said.
“Daniel is a fantastic player with a great technique, has a lot of experience, and is someone who will strengthen our midfield options.
“He can play as a holding or offensive midfielder and is also very good on either wing.”