As everyone has said, he originally was not Irish. His original name was "Cosney Megundal," which is not a real name in the slightest, but an Anglicized transliteration of a Japanese phrase for offering someone money (to reflect his outward persona as a philanthropist and his true identity as a loan shark).
I wondered
why they made this change while playing 1-3 until some things stood out to me.
-He's depicted as having made his fortune through money lending at high interest and terrorizing "respectable" people for the loan payments. The fan translation has van Zieks call him a usurer, which is the religious term for charging exorbitant interest on a loan; the official localization calls him a
shylock
-He's a greedy Victorian-era villain with so much money that he can control everyone around him
-He
induces a child pickpocket in the slums of London to work for him as part of his criminal activities
"Deceptive, rich money lender who extorts Englishmen, is all powerful due to his wealth, and induces children to crime" is certainly a stereotype in Victorian English literature,
but it's not an Irish
stereotype.
As soon as van Zieks said "shylock," I immediately wondered if someone on the localization team caught that implication and decided to give McGilded an explicitly stated different ethnic identity to weaken the implication.