Disc-based language-learning company Rosetta Stone (RST) is moving farther online.

On Tuesday, the Arlington, Va.-based language tutor announced that it has just bought Seattle's Livemocha online language-learning business for $8.5 million cash, bringing a customer base of 16 million Livemocha members into the Rosetta Stone fold.

Already moving in the online direction, Rosetta CEO Steve Swad says today's purchase "accelerates Rosetta Stone's transition to cloud-based learning solutions" and furthers "the process of transforming Rosetta Stone to be the most dynamic and ubiquitous technology-based learning platform in the world." It also gives Rosetta the option of offering its customers "a low-cost or even free alternative product to offer learners around the world."

According to the company's press release, Livemocha boasts 16 million members from 195 different countries, "all teaching, learning, and interacting online."

Turns out Livemocha is popular with investors, too. After announcing the deal, Rosetta saw its shares shoot up more than 4% to $15.67 for the day.