Langerak, who has made eight appearances for the Socceroos, helped Stuttgart earn promotion back into the Bundesliga.
Langerak, who has made eight appearances for the Socceroos, helped Stuttgart earn promotion back into the Bundesliga last season by winning the second division title.
However, he found himself on the bench when coach Hannes Wolf chose new arrival Zieler, a 2014 World Cup winner with Germany who joined from Leicester City, for Stuttgart's first two Bundesliga games this season.
The 29-year-old Langerak, who spent five years at Borussia Dortmund until joining Stuttgart in 2015, has signed for Levante until 2019 with the deal reported to cost one million euros ($1.2 million).
"Mitch earned his place as one of the cornerstones in our return to the Bundesliga," said Stuttgart director Michael Reschke.
"Understandably, he had a problem being comfortable with the role of number two."
Langerak has been replaced by Adam Federici in the Australia squad for the upcoming 2018 World Cup qualifiers against Japan and Thailand so he could complete the transfer.
"Mitch has some issues at club level that he needs to resolve," said Australia coach Ange Postecoglou.
"Speaking with Mitch, it was in our mutual interests that he focus on that at the moment rather than come into camp."
Stuttgart have already signed Langerak's replacement by giving a contract to goalkeeper Alexander Meyer from fourth-tier Energie Cottbus.