The J in Jason becoming an S is based on the model of Seán being the Irish version of John, and of Séamus being the Irish version of James. Séason would be pronounced Shay-son.

T is pronounced very softly in Irish, and when it’s followed by an E, it becomes a CH sound. The EA diphtong in Tead is pronounced as ‘ah’. So Tead would be pronounced as Chad, exactly the same.

As above, the EA is pronounced ‘ah’ and the combination GH is silent in Irish, so Hearraigh would be pronounced as Harry is in English, despite the initially alarming length.

Darach is already an Irish name, meaning ‘like an oak,’ and it’s usually Anglicised as Dara or Darragh (pronounced identically to each other), so suggesting Dairech = Derek is just extra funny.

I don’t think I’ll actually be able to scrub Ailfiagh out of my mind. It sounds too Irish, to the point that it’s replaced Alfie as the default spelling for me.