A language needs a fix
Most of suggested translations/answers are often given with "THE subject verb THE object". But I'm pretty sure it would be better to put A more than THE. After all Jaquen H'guar always speaks in third person and with indefine articles, as if this is a peculiarity of his muño ēngos (mother tongue).
Another MORE important reason is to help new learners tell apart words like Unsullied. Yes, Dovaogēdy is nominative singular while Dovaogēdi is plural, but (due to Duolingo intuitive/deductive approach) in English The Unsullied could easily be confused between sing, and pl. SO, this way An Unsullied would directly remind you of Dovaogēdy
Jaqen H'gar speaks like this because he is a Faceless Man and they treat people as without identities, not because of the Valyrian he speaks (which he has never spoken on the show). Just clearing that up.