Áit means place. (i)úil means to do with or to make something an adjective. Like -ish. So áitiúil literally means "place-ish"
"local" comes from the Latin "localis" meaning "pertaining to place(locus)". So English uses a Latin adjective with an Old English noun (which may have been derived from a different Latin noun). Irish just uses an adjective that matches the noun!
Gadh mo leithsceal nil Gaeilge mo mhaithairtheanga.
Now, how do you say you like local, organic food?
Is maith liom bia orgánach áitiúil