Based on the comment: “...idiomatic might have been the wrong word; I meant in the sense of ‘non-English speakers will immediately know what I mean’”
I believe that the c. 1983 Basic Set is still the edition that was published in the widest number of languages. Looking at the covers that they have pictures of here—Basic Set foreign editions—nearly all use the English “Dungeons & Dragons” on the cover. The one exception is France where it says “Donjons & Dragons”.
So, in Esperanto, it perhaps would be best to use the English name to qualify whatever Esperanto translation you might like. As it seems the English name is likely recognizable to anyone who has encountered the game even if it was only through a localized version. e.g.
Ni ludis Danĝerejojn & Drakojn (angle: Dungeons & Dragons).
Update: For an additional data point, I checked every non-English Wikipedia page linked to by the English D&D Wikipedia page. Of the 42, only 11 did not use the English name for their title. Only one of those, Scots, failed to mention the English name in the body of the article.