The choice of languages is a feature that was introduced in weekly snapshot 11w49a and officially released in Minecraft 1.1. The language menu is accessible via a new button in the main menu to the left of the options button, and from the options menu.
Unknown (probably because Austrian German mostly equals standard German)
Español (La)
Latino-American Spanish
South America
11w49a (1.1.0)
12w01a (1.1.0)
Replaced by Argentinian, Venezuelan and Uruguayan Spanish translations.
Magyar
Hungarian
Hungary
11w49a (1.1.0)
12w01a (1.1.0)
Unknown (there is a hu_HU.lang file in the directory, but it contains Bulgarian)
Malti
Maltese
Malta
11w49a (1.1.0)
12w01a (1.1.0)
Unknown (removed from the Translation Project page as well)
Bugs & Inaccuracy
In 12w04a, the Afrikaans singleplayer button contained an expletive. Jeb has apologised for not reviewing the submissions since.
Arabic is a language that is always written with connected letters, however, in Minecraft the letter do not connect (e.g. "اللغة العربية" is written like "ا ل ل غ ة ا ل ع ر ب ي ة")
If you choose Spanish (MX), Clicking Options, then Controls will crash the game. You must delete your options.txt or else the crashing will continue.
In some languages, the text is too long and overfills the button it is written on.
Splash texts are not translated and therefore will show up in English.
In Canadian English, the "Benchmarking" achievement description is bugged. Also, Gray and Light Gray Wool spell the word "Grey (English spelling)", but the dye spells it "Gray".
Power and punch enchantments on bows have the name of the similar sword enchantment when using Canadian English
Many Turkish translations contain obscenities, which were contributed by trolls.
There are some critical mistakes in some of the aTranslations, like Hebrew.
The UK English and Canadian English use the other languages code.
I.E: Name = Canadian English, Language code = en_GB and vice versa.
In Pirate, the "Industrious now, aren't we?" (Make a crafting table) achievement has a 'n' on the end.
Hebrew is titled as "אנגלית" (English). It should be "עברית" (Hebrew).
When Bulgarian is selected the text beneath is in Hungarian, what was removed for unknown reason.
UK English spells 'Connection lost' as 'Connextion lost'
In 12w05b When saving the world the "saving chunks" will show up (tested Chinese "both versions" and in Vietnamese)
In the Canadian English translation in snapshot 12w06a, some items names have been tampered with. Examples include: Snowball (Weapon of Mass Destruction); Diamond Boots, ay; and Snow block (Igloo material).
In the Canadian English translation in snapshot 12w07a/12w07b, Multiplayer is replaced with "Go Camping with your Buddies, Eh?"
Trivia
Minecraft is available in three fictive languages : Klingon (Klingon language from Star Trek), Pirate (Internet language) and Quenya (Elvish language from Lord of the Rings).
In Pirate speak, Gold Boots are called "Buttershoes", a reference to Seananners, a well known YouTube personality that ran a Minecraft series.