Well, I personally believe, that the greatest Darkness Dragon names, are the ones that go with the Element, such as:
Shadow
Spirit
Mist
NightShade
and others.
Sorry if i repeat any answers
Yami means darkness in Japanese
yoru means evening in japanese
kagayaku means shining in japanese
onyx is a black stone
onikisu is onyx in japanese
minuit is midnight in french
kuraku is dark in japanese
maho is magic in japanese
yonaka is midnight in japanese
kanashimi is sorrow in japanese
utsu is depression in japanese (i think?)
akumu is nightmare in japanese
sorry if i got some of the translations wrong. I tried at least! ;)