Language learning platform Duolingo announced it has raised $35 million in a Series H funding round from Durable Capital Partners LP and General Atlantic.

Duolingo will continue to invest into the R&D of its suite of global language-learning products as well as to accelerate the growth and expansion of its team with the capital. It has to date raised a total of $183 million at $2.4 billion valuation.

Founded in 2011, Duolingo provides free learning content of 39 languages via its app, and gains revenue with advertising and a paid subscription offering Duolingo Plus, which removes ads and provides other additional features.

The company has over 500 million total app downloads and over 100% revenue increases during each of the past three years.

Another product Duolingo English Test (DET), an online alternative for students to show English proficiency to overseas higher education institutions, has witnessed a skyrocketing increase during these months. The test has a 1500% year-over-year growth in test-takers.

Last year Duolingo went into China, and has already developed courses of six languages, including English, Japanese, Korean, French, Italian, and Spanish. According to the unicorn, more than 15 million people in China are learning on the platform, and China ranks one of the most fast-growing markets. 

In the US market, Duolingo launched a product called Duolingo ABC to teach children ages 3-7 how to read in March.