I am a Foley who recently learned my ancestor Patrick Folan emigrated from raheen parish co. galway about 1863. I had not previously know about this name foley - folan name change which seems to have taken place for many folans after they arrived in america. Pat Folan's statement
"The accepted Irish language version of Folan is "Ó Cualáin". This is interstingly also the Irish for Foley"
is intriguing but i cannot find any other reference for "Ó Cualáin" being an accepted Irish language version of Foley. Naturally it would be an accepted Irish language version of Foley for those Foley's who had previously had the surname of Folan but I'm not sure if that's what he was meaning to say.