"He is not there yet."
Translation:Níl sé ansin go fóill.
The fada on the o matters, and the standard spelling has 2 ls (though fóil with one l is listed in the FGB as a variant spelling of fóill). Even if "foil" was a word in Irish, it's pronunciation would be quite different from fóill.
(If you need convincing about the importance of the fada, look up the Irish for "cake")