This is the A814, on the approach to Dumbarton from Cardross, at the boundary of West Dunbartonshire and neighbouring Argyll and Bute.
"Welcome to West Dunbartonshire / West Dunbartonshire and Beauvoisin, France / celebrating friendship / célébration d'amitié"
(The Beauvoisin referred to there is in the Languedoc-Roussillon region.)
The building on the right, almost directly behind the road sign, but only faintly visible through the trees, is
NS3775 : Cats Castle.
By mid-2016, this sign had been replaced by one with different wording: it has English and Gaelic text, and the twinning is no longer mentioned:
NS3775 : Entering West Dunbartonshire.