ARGLWYDD IESU GRIST
FAB DUW.
BYDD DRUGAROG WRTHYF,
BECHADUR.
(N.B. ‘mab’ takes soft mutation here as it is a ‘noun in apposition’, and ‘pechadur’ also takes s.m. as it is in the Vocative Case)
… although the version favoured by the Church in Wales doesn’t treat the word ‘mab’ as being in apposition and therefore doesn’t apply soft mutation. Hence …
‘Arglwydd Iesu Grist, Mab y Duw Byw, bydd drugarog wrthyf i, bechadur.’
N.B. ‘Mab y Duw Byw’ = ‘Son of the Living God’
Thank you Gareth
Warning – grammatical aside! 
Actually the other way round, sort of: bechadur is in apposition – meaning two different noun-phrases used to describe the same thing. In English, “on me, a sinner” isn’t talking about two different people, they’re two different ways of describing the same person: compare, “Former Plaid Cymru leader Leanne Wood said today…” or “Leanne Wood, former leader of Plaid Cymru, said today…”
“Son of God” is actually in apposition to “Jesus Christ”, but it’s also (unlike bechadur) in the Vocative: in languages that have grammatical cases, the Vocative case is the one used for talking directly to someone, and in this case you’re addressing your prayer directly to Jesus. There’s a famous autobiographical anecdote by somebody about learning Latin – “mensa, mensa, mensam – table, O table!, a table” – being told by their teacher that the vocative is the case you would use to address a table…
I know Gareth King says that nouns used as vocatives get a soft mutation – pace the Church in Wales – but I didn’t know about nouns in apposition. (Or is it just because bechadur is following i? – the only things I can find on apposition all say “after a proper noun” i.e. a name, e.g. Branwen Ferch Llŷr.)
Crikey Richard you’ve lost me there, I’m not a grammarian, I’ll just have to assume you’re right as it sounds like you know a lot about your subject. Thanks for your contribution though.
“Arglwydd Iesu Grist, Fab Duw, trugarha wrthym,
pechaduriaid.”
That’s the Jesus Prayer in Welsh. I’m not a Welsh speaker yet, only on week 6 of SSiW as of now, but my husband and I are Orthodox (he’s in seminary to be a priest actually!) and are learning Welsh together. We happened to be in touch with a priest in Wales who gave us this text, as well as some other things. 
Thank you Kari!
Just out of interest Kari, which part of Wales are you in?
I’m not in Wales, unfortunately. We live in the US, although we’re moving to Ontario next month for my husband to finish his divinity programme. We’re hoping to end up in Wales some day soon, though.
That’s interesting. What is your interest in Wales, if you don’t mind me asking? Just curious. There aren’t that many Orthodox Christians here. Not that I am Orthodox. I’m RC though I don’t practice at the moment.
We’ve visited in the past and loved it very much. We know we’ll be somewhere in the UK when he’s finished up, as the Orthodox presence there is growing, so we’d love to end up in Wales if we could. If not, we figure we’ll be visiting Wales a lot regardless, so might as well learn the language and be able to converse.
That’s interesting. I know that in Ireland some disaffected Catholics have turned to Orthodoxy, but I didn’t know it was increasing in popularity on the mainland. I’ve always thought it was Evangelicalism that was doing well compared to Catholicism/Anglicanism/chapel religion. Well, I hope you end up where you can do the most good!
So sorry for this necrobump, but does anybody know the Paschal Troparion in Welsh?
Here it is in English
Christ is risen from the dead
Trampling down death by death
and upon those in the tombs
bestowing life.