Outside the Courthouse , Mulgrave St. Limerick is a sign:
Ceadaithe Pearsanta Amháin
Permitted Personnel Only

Is this correct? or is it another instance of "Google Translate" Should it be "Pearsanta Ceadaithe" or better still "Pearsanta atá ceadaithe amháin"

For fun I used Google Translate which gave me

Pearsanra Ceadaithe Amháin. It looks OK but maybe other input from other people would be enlightening.

Foireann is also used for "personnel" but I wouldn't know which is better.

"Pearsanta" means "personal", which wouldn't be correct.

I have a feeling that people who know the language well may say it differently.

The authorised version (from 'téarma.ie'): Pearsanra Údaraithe Ámháin

... which Google translates as "Unauthorized Personnel"

But it is Amháin, an chéad A gan síneadh fada, which Google translates correctly (Only Authorized Personnel)