Translation:Ar an Luan.
I've read that both ar an Luan and Dé Luain mean "on mondays". Does one refer to mondays in general and the other one to a specific monday?
Dé Luain is generally “on (a specific) Monday”, but could mean “on Mondays” in a sentence with a verb that has a habitual aspect.
In Hiberno-English we say "On THE Monday" usually to mean a Monday in the future, not necessarily next Monday. "Ar an Luan" has nothing to indicate plurality so I think it's wrong to say it means "on Mondays."