Guess what? Today, while driving, I saw an ambulance with the lettering on the front above the windscreen just as you show it here.
I have not seen this before. Perhaps it occurs in countries which typically read from right to left (as in Arabic) and is the next big change to English writing! The ambulance word was written as expected on the sides and back of the ambulance, 'correctly'.
I think it shouldn't matter what your language is or which direction you read. I think there are enough other easy clues to help anyone identify an ambulance for what it is, even when the word is spelt the right way round and have to see it backwards in the rearview mirrors. After a short time, people would know what the world ambulance looks like backwards. But as I said, with the siren going and the red cross here, and the fact that all ambulances in any country look much the same and nothing like anything else, I think that should be enough for anyone to recognise it quickly.