Imagine that all the humanoid and demi-human laguages are actually the same, but pronounced with outrageous accents and bizarre idiom. All the elves have a French accent, all the Dwarves have Swedish, Dragons have a Pakistani accent...
A village where everyone goes blind sometime during puberty. What could be causing this? Perhaps something in their diet. Or some malignant gene. How would an entire village where only young childen can see function?