In the BBC adapatation of The Iron Hand of Mars, a novel by Lindsey Davis, one of the babarian Celtic tribes over the Rhine in Germania Libera (Free Germany) speak Welsh. While I do know quite a few Welsh-speaking Germans now, back then they certainly didn’t speak Welsh in that area.
The story is set in 71 AD and involves the chief protagonist, Marcus Didius Falco, being sent on a mission by the Emperor Vespasian to investigate various things along the Rhine, which was then the frontier between the Roman Empire and Free Germany. Various tribe lived in that area, including Celts, Balts, Scythians, Sarmatians and Alans, and some of them probably spoke Celtic languages distantly related to Welsh.
In the radio play it sort makes sense to have the actors playing the Ancient Celts speaking a modern Celtic language – very little is known about the language they spoke back then, so that couldn’t be used. To most listeners, the language would sound foreign and maybe a bit Celtic. As a Welsh speaker though, it was funny to hear Welsh used in this way, but good to be able to understand everything, and nice to hear Welsh being used.
Have you come across other examples of modern languages standing in for ancient languages, or even for alien languages, in this way?