Merci avoir un bon jour no, that's French
Lá breá a bhí ann.
Irish Gaelic?
Just say it exactly the way you want to say it, there's no "one" way of saying thanks to someone for being nice.
To say "have a nice day" in Igbo, you can say "Ika nke ọma."
nice day
Go raibh maith agat as éisteacht
If you would say "Thanks for the directions, have a nice day" in English, you would "Merci pour les directions, bonne journée."
Golgu todu show du
In Venda, you would say "Ua livhuha ndi mini" to say Have a nice day.
Say Something Nice Day in 2011, in June 1st.
Go deas bualadh leat.
Tá folt breá ort