It'll be grand
National policy. Applied to every problem from a flat tyre to the end of the world, ideally with a cup of tea.
De roof's leakin', de car's banjaxed and de dog ate de rent. Ah sure have a cup of tea, it'll be grand.

Shall I translate it into posh English for you, head?
Ah, there you are. Here it is in posh English.
The roof admits the rain, the motor car is ruined and the hound has eaten the rent. Pray, take some tea. All shall be well.
Questions
What does it'll be grand mean in Ireland?
National policy. Applied to every problem from a flat tyre to the end of the world, ideally with a cup of tea.
How do you use it'll be grand in a sentence?
“De roof's leakin', de car's banjaxed and de dog ate de rent. Ah sure have a cup of tea, it'll be grand.”
Updated
On the list: Irish slang phrases