User Dedalvs has been in charge of developing the language learning program, which will teach users the language of Daenerys Targaryen. They've been updating interested users on development progress for the last eight months. Yesterday, according to Reddit, an update was posted that says, "Valyrio Māzis," which translates to "Valyrian is coming." While the update seems to have disappeared from Duolingo's site, the project's estimated completion date is July 13th
Language app Duolingo has three phases for testing new languages and new language combinations on its site. You can see everything the service is working on in its Incubator. Phase 1 consists of limited testing by volunteers, Phase 2 is a public beta and Phase 3 courses have been finalized and released as finished products.
Edit: Duolingo reached out to let us know that the High Valyrian course is set to be released on Thursday, July 13.