DEH-wee. e = short 'e' sound, i = ee sound Emphasis on the first syllable.

Mae 'Dai' yn enw arall.
('Dai' - pr. die - is another name.)

There is very little regional variation in this, if any at all. Occasionally, I've heard names 'officially' mispronounced in areas that are heavily anglicized, like 'Hue-well' for Hywel, instead of HUH-well. But I've never heard a native Welsh person say anything but DEH-wee.

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