MA-bih-NO-ghee-on is a fair approximation of the Welsh (hard 'g' formed with a labio-palatal seal, not the softer jay sound formed in the front of the mouth) - in my transliteration 'ghee' rhymes with key.

Just to avoid a misunderstanding, the Mabinogion are ancient tales, handed down by the oral bardic traditions of Welsh culture, and only set down in written forms in comparatively recent times (500 years!) I think Lady Guest was just a Victorian dabbler in translations, tho' I am probably being cruelly dismissive of her scholarship. I'm drawing attention to this only because I *know these works as one of the ancient glories of British storytellers' art, and it was only re-reading my post I suddenly realised I was quite unreasonably taking it for granted that others would know about them. Anyone who is now discovering them is in for a treat - an extraordinary mix of the personal, the social and the cosmic/allegorical.