Sorry - I should have been more careful:

In (Irish) Gaelic, this greeting is written:

Dia dhuit

So the change in the consonant question only arises with the second word. Strictly, grammatically, there should be no h there. However it is ALWAYS pronounced as though it's there and USUALLY written explicitly.

Brought up on Munster Irish, I render "dh" as, roughly, gw as shown - but you will certainly hear it as y - especially in Donegal. Hence the similarity to Scottish Gaelic.

Regards