The two goalkeepers were together last season at Melbourne Victory.
Langerak made his first team debut on Saturday in victory over Bayern Munich and Moss told tribalfootball.com: "Mitch and I were great mates at the Victory.
"He's a really good kid with a strong work ethic. It’s not surprised me he's gone on to bigger and better things. We stay in touch and I know he's loving life at Dortmund.
"He says he's never worked so hard!
"I expect him to be in the (Australia) national team set up very soon."