I don’t think this is a bug, but rather intentional because Blizzard did not reach an agreement with the voice actors so therefore no dub came for this particular patch.
Edit:
Remember reading it up earlier at reddit - it was because of an AI voice source issue though unconfirmed.
https://www.reddit.com/r/wow/comments/1hgz6wq/blizzard_is_killing_dubbing_on_other_languages/