There is absolutely no evidence for the Picts in Ireland. They assimilated with the Gaels(Dal Riata) and are the descendants of todays Scottish people. They were thought to be a P Celtic speaking people, In Adomnáns Vita Columba he speaks of Colmcille using an interpreter to converse with one of the Pictish leaders when travelling through Pictland.The source of evidence for P-Celtic in Northern Scotland is placenames, these provide such P- Celtic elements carden(eg. Pluscarden, Kincardine)cognate with Welsh cardden thicket.
Good reference for the Picts is Languages of Britain and Ireland, edited by Glanville Price, published by Blackwell.