Daenerys Targaryen’s impressive language skills in locations in Essos, Game of Thrones created several fictional languages specifically for the series. Daenerys (and by proxy, Emilia Clarke) became well-versed in each of the languages, which most prominently included Dothraki and the Targaryens’ ancestral High Valyrian.
House of the Dragon, which follows the Targaryen family dynasty 200 years before Game of Thrones’ timeline, will finally showcase the fabled house at the height of their reign. Not only will House of the Dragon lean into the most notable aspects of the Targaryens like their many dragons, but also the culture of the family that separated them from the rest of the noble houses of Westeros. Much of this will involve their history and origins in Old Valyria, which will receive far more prominence in House of the Dragon’s Targaryen-centric story than in Game of Thrones.
Since House of the Dragon is presumed to primarily take place in Westeros, the prequel series isn’t apt to feature nearly as many cultures and languages as Game of Thrones. However, House of the Dragon will prove why Dany’s ability to still speak High Valyrian was so important in connecting to her Targaryen ancestry. House of the Dragon’s characters are confirmed to speak High Valyrian far more often than Dany did in Game of Thrones, which makes sense considering how many Targaryens are alive in the prequel. While Dany could only speak Valyrian to those from Essos who still understood the language or to her dragons, House of the Dragon’s Targaryens can use the language to further separate themselves from the other families. Many of House of the Dragon's noble families in Westeros were likely taught High Valyrian by their maesters, but they won’t be as fluent or able to find as much use of the language as the Targaryens do. In moments when House of the Dragon’s Targaryen characters only want to speak to each other, they’ll likely use High Valyrian to exclude of other families from conversations.
Why The Targaryens Still Speak High Valyrian In HOTD & GOT
One practical reason why the Targaryens still speak High Valyrian in House of the Dragon and Game of Thrones is that the language is used to command their dragons, at least in the case of Daenerys. The most logical reason for this is that the historic Targaryen family of Old Valyria had communicated with their dragons using the language, so the dragons could likely still understand Valyrian in later generations. Dany may have also used High Valyrian in order to differentiate her commands to her dragons from casual conversation in the common tongue, but it seems more probable that the Targaryens had always used Valyrian to command and train their dragons.
Family history and heritage are extremely valuable to House Targaryen, so maintaining the language of their ancestors even long after the dragons died out would still be important. The Targaryens continuing to teach later generations High Valyrian despite it being a dead language also isn’t as shocking as the other Valyrian customs that the family has kept, such as the Targaryen royalty's incest and polygamy. As a language that has no continued personal attachment to any other family in Westeros – even to those who also descend from the Valyrian Freehold – familial fluency in High Valyrian is another way to bring the Targaryens closer together while establishing them as a separate entity from the other Westerosi noblemen in both House of the Dragon and Game of Thrones.