Even if Australia win the series 3-0, it won't be enough to overhaul South Africa.
Langer said the confidence Australia gained from their series win against England would hold them in good stead for more success.
"You can see there's steel in Michael Clarke's eyes," he said.
"He's been saying for the past 18 months he wants to become the No1 team in the world again. They'd take great confidence from their win over England."
Langer said the current focus within the team was clear.
"If they can beat a very good England team 5-0, then of course they can become No1.
"If they can keep Ryan Harris, Peter Siddle and Mitchell Johnson on the park, and combine that with Nathan Lyon's progress, [then they're a chance]. But you don't become the No1 team in the world by winning one great series."
Langer, who averaged 45.27 during his 105-test career, retired after Australia's 5-0 series win over England in 2006-07.
The 43-year-old, who coaches Western Australia and the Perth Scorchers, said he took great joy from watching Australia pants England.
"It was magnificent," Langer said.
"When it happened in 2007, I'm sure a lot of people would have wondered if it would ever happen again.
"The beautiful thing for me is they stuck with the same team and got success."
- AAP