Yesterday, Diablo III players from across the world encountered errors 81, 82, and 84 when trying to play the game. As it turns out, these errors occur when you're trying to play in a language foreign to your native region.
What this means is, for example, if you were on vacation on Mexico and realized that the game is about $3 cheaper there and bought it, you'd be forced to play in Spanish, despite paying full price for the game. This issue seems to be affecting Latin America, Eastern Europe, Russia and buyers who bought the game in a foreign country.
So far, Blizzard's response has been unhelpful. They claim this is working as intended; they are selling copies of the game with language limitations, with no warning whatsoever in any part of the box that I've found. The most "helpful" answer they've given so far is to buy another copy of the game from their site and once they verified you own both keys of the product, they can "gift" your old key to a friend.
This would make you lose all progress you'd made on your old copy. Currently, there's a website dedicated to all who have been affected by this issue, so if you've been affected, feel free to leave your details and a comment. If you're about to buy the game, I'd recommend doing so from the Blizzard store, as this copies do not seem to have any language limitations at all and they cost the exact same price you'd pay if you'd buy it in a retail store. In the meantime, let's hope Blizzard comes to its senses and we can all play our games the way we want.
Here's a few links to the official forums of people experiencing the problem. I urge you to contribute if you are having this issue too, as that's the only way Blizzard will listen to us: