"Dewi Lingo ydy o."
Translation:He is Dewi Lingo.
Yes, most questions start with 'ydy' in the third person. However this is a special emphatic sentence we use for names (and also jobs), as introduced in Greetings 2, although we cheated a bit in Greetings 2 by not using the full form of the written verb only the shortened spoken version. So for the singular we would write ....'Dewi Lingo ydw i' (I am Dewi Lingo), 'Dewi Lingo wyt ti' (You are Dewi Lingo) and 'Dewi Lingo ydy o/e' (He is Dewi Lingo).
It's a Welsh equivalent of "David". It's the name of Wales' patron saint too: Dewi Sant "St David".
Yep, it's a common Welsh name. Another (later) version of David is Dafydd, which is probably even more common in Wales.
Not in Wales, but from some initial googling it is clearly female in other parts of the world. Possibly with a different pronunciation?