"Bain sult as an oíche amaitéarach" means "Enjoy amateur night"
Bain sult as do nóchadú breithlá (or Bain sult as do 90ú breithlá)
sult as a command Bain sult as - Enjoy (it)!
Bain sult as do dhaicheadú breithlá (bain sult as do 40ú breithlá)
Bain sult as d'ochtú breithlá déag (Bain sult as do 18ú breithlá)
Bain sult as do 45ú breithlá (Bain sult as do chúigiú breithlá is daichead)
In Irish it's "Bain sult as do naonú breithlá caoga" (or Bain sult as do 59ú breithlá)
In Irish it's "Bain sult as do chaogadú breithlá" (or Bain sult as do 50ú breithlá)
Bain sult as.
bain sult
In Irish it's: Bain sult as (singular) / Bainigí sult as (plural)
To say "happy 80th birthday grandad" in Gaelic, you would say "Lá Breithe Sona 80 chun na haoise do mhórathair."
In Irish it's "Bain sult as d'ochtú breithlá déag, Leen" (or Bain sult as do 18ú breithlá, Leen)