Without a penny spent on advertising, Duolingo, a United States-based language-learning application, has become the largest online educational app on iPhone's iOS system and Google Play, gaining 30 million users in the two years since it was launched.

The startup, with 35 employees, plans to replicate its business miracle in the West by launching its app in China to help Chinese people learn English.

"There are 250 million people learning English in China," said Luis von Ahn on Tuesday. "The market is humongous."