[James2001]

That proves XIII's point then, doesn't it? It won't be as easy to find coaches as it sounds on paper.

There's more musicians in Wales than just Tom Jones!
Wynne Evans (the Go Compare man) already hosts shows on S4C (IIRC, he actually learned Welsh as part of an S4C show which had non-fluent Welsh celebrities learning the language- and then went on to present a later series! So clearly did well on it), so he's a possible choice.

A bit of research shows H from Steps took part in a different series of the same show as Wynne... though whether he became proficient enough to do something like this, I don't know, but he's another possible choice if he is.

Aled Jones is well known and a Welsh speaker too. And to be fair, who they pick to judge doesn't have to be that well known either, even if it's only a fifth of the Welsh population who can speak the language, there's still a reasonably sized pool to pick from.