Alfred J quack was the one I was thinking but not its Wil Cwac Cwac. Fireman Sam is also welsh.
Wil Cwac Cwac was made for S4C in Welsh and for TV-am in English.
You find a lot of productions for CBeebies are co-produced with the likes of ARD/ZDF, RTÉ and S4C.
I remember Wil Cwac Cwac being shown on CITV in late 1984. I think those episodes were credited to BBC Wales, and Central tended to mix out of the credits early (to a CITV still) to avoid the BBC credit going out on ITV!
CEEFAX SUBTITLES BEGIN SHORTLY