Well, first of all it's a surprise to me that he wrote any Scottish novels, being a bit French himself - Auld Alliance notwithstanding - but it seems he was in fact Breton with a Scottish
Two of his novels are set in Scotland. One, The Green Ray is a romance revolving around the appearance of a physical phenomenon, the green flash. The other, Les Indes Noires is the one being issued in a new translation.
Les Indes Noires appears to have been published under more than one English title. It is most literally translated as Black Indies, a reference to the wealth of Britain's coal deposits. The other titles include: Black Diamonds, Child of the Cavern and The Underground City. It's under this latter title that it's being re-published.
The Luath Press edition is a complete retranslation, as previous translations were abridged, and it is to include copies of engravings from the French first edition.
I haven't read it yet, so I don't have an opinion on it but it sounds interesting. It is apparently a somewhat utopian view of a future in which the discovery of vast coal deposits beneath Loch Katrine lead to the establishment of the underground Coal City of New Aberfoyle, full of happy, cheery miners. The Gaelic-speaking child mentioned in some versions of the title has never seen the sun, before taking a trip up Arthur's Seat in Edinburgh. It also features a giant owl, so it must be a good book! It seems - unsurpisingly - that there is a whiff of the kailyard to it, but sometimes there is good stuff to be found hidden under tartan and sentimentalism.
I may take a look at one of the existing translations before deciding whether to splash cash on a new copy.