You can't really blame Powys Highways for some of the rather dubious bilingual signs appearing on Radnorshire roads - after all they're only following the advice of Bwrdd yr Iaith's Place-Names Standardization Team.
The latest example I've spotted is Llandeglau/Llandegley. I can see how this name Llandeglau has been created, and it is surely a creation rather than a name with any historical validity. No doubt it originated with the book Rhestr o Enwau Lleoedd / A Gazetteer of Welsh Place-Names (Elwyn Davies, 1967) and comes about from a standardisation exercise where incorrect English spellings ending in ley are Cymricised as lau, for example Dolgelley/Dolgellau. Now Llandegley is an incorrect spelling, but of Llandegle not Llandeglau. Richard Morgan's little book has an example of Llandegle dating back to 1291, while it is also the form used in the 15C bard Lewis Glyn Cothi's praise poem to a local patron, one Ieuan ap Llywelyn Fychan: Hyd Glud a Llandegle wen - to the Radnor Forest and fair Llandegle. The spelling Llandegley appeared much later on the scene in 1557. More recently Ffransis Payne, who lived in the parish, used the form Llandegle in his wonderful volumes about Radnorshire, Crwydro Sir Faesyfed.
The sensible solution would have been to just use the correct Welsh spelling Llandegle on the signs. This would have been cheaper, historically accurate and would not leave Radnorians thinking that their pronunciation of the name was English, when in reality it is Welsh and as old as the hills. Hopefully someone will get it right when they do the bilingual version of this.