From the company press release:
Since the Iranian election last week, people around the world have increasingly been sharing news and information on Facebook about the results and its aftermath. Much of the content created and shared on Facebook related to these events has been in Persian – the native language of Iran – but the users have had to navigate the site in English or other languages.
Today we’re making the entire site available in a test version of Persian, so Persian speakers inside of Iran and around the world can begin using it in their native language.Persian was already in translation before worldwide attention turned to the Iranian elections, but because of the sudden increase in activity we decided to launch it sooner than planned. This means that the translation isn’t perfect, but we felt it was important to help more people communicate rather than wait.