‘Conas atá tú? , ‘How are you’, is my salutation of choice.
‘Dia duit’ is an expression that I definitely keep my ear open for in conversational Irish class, primarily to find out any other possible greetings.
One of the notes this year was the pronunciation and spelling – there is the sound of a h (Dhuit) when spoken but it is spelled as ‘Duit’.
This is confirmed in focloir.ie as well as my copy of Buntús Cainte. The ‘Irish Grammar Book’ by Nollaig MacCongáil states that ‘in speech this initial d is pronounced as if it were lenited’, as in ‘dhuit’.
All this was fine and mentally filed away appropriately – and then the C.S.O. had to upset matters.
Pota-Focal does have ‘Dia dhuit’ as an alternative to ‘Dia duit’ citing examples from a few Irish-learning books. Online discussions indicate that ‘Dia duit’ is standard Irish but regional variations arise with different dialects.
Once again, language proves that exceptions, differences and new versions are always possible.
As to why the Central Statistics Office departed from standard Irish, I do not know.