Proper translation:
[Event] Diablo III has reached its second birthday!
2 years ago on 5/15, the gates of the Burning Hells were opened and Diablo III revealed itself to the world. The time has now come for Diablo III's second birthday.
To celebrate the 2nd anniversary of Diablo III, we're giving special benefits to everyone who logs into the game to defend Sanctuary! Starting from 5/15, for a week, legendary drop chance is increased by 100%, and you'll also get double Rift Keystone Fragments. This 2-year anniversary buff will start on 5/15 Thursday noon and will last until 5/22 Thursday night. (Ends at 00:00 Friday)
Have a great time, Nephalem champions! Thank you all for your interest and support, and may you have amazing adventures in the future as well!
* The buff will only be available on PC. This buff affects all characters that are playing the game, and stacks with all other similar bonus effects.
edit: Times are for Korea, so the timing may be a little bit different for other regions.
http://www.reddit.com/r/Diablo/comments/25in42/diablo_3_two_year_anniversary_drop_buff/