Managed to find Trefor & Vicki's CD and listen to it. They sing it in Welsh first, then in English after an instrumental break. Here's what I make of the English - very close to non-singable translations posted above.

ALL THROUGH THE NIGHT
(Traditional Welsh. English translation by Trefor & Vicki Williams)

The twinkling stars all tell their story,
All through the night,
"Here's the way, the road to glory,"
All through the night.
Any other light is darkness,
Showing beauty true and witness
Heaven's family rest in silence,
All through the night.

O so bright the star is shining,
All through the night,
And her sister, Earth, she's lighting,
All through the night.
When age's ill comes like the night,
Then to beautify man's twilight,
We must all share our own daylight,
All through the night.