You know what doesn't make any sense? Canine "accents", you know like Scooby Doo or Astro from the Jetsons. I mean, if dogs suddenly had the ability to speak English or some other human language I seriously doubt they'd go "I ruff roo Raggy!" Or would they? I mean, "barking" doesn't so much involve enunciating "woof" as just vocialising their natural call. We don't enunciate when we cough, it just happens, that's why we don't speak in cough... at least not by accident.

Anyways, why does Scooby Doo talk anyways? Throughout the cartoon's history I do not ever remember hearing some explaination as to why Scooby talks, or Astro for that matter. At least you can speculate about Astro, in the future dogs will evolve the ability to talk, or at least will try too.