Currently, Apple provides the Siri Supports in following languages - English, French, German and Japanese. The Support for Japanese was announced recently when Apple launched the third generation iPad, which is called as New iPad. While Apple is thinking to add Siri support for Italian, Chinese, Korean and Spanish languages later this year.
Coming to the hacking part, Kunal Kaul provides the Siri that can speak in Hindi with his hack. Kunal has used his Google API server which is connected by the Siri to make interaction in Hindi. Problem only is that Siri is able to answere in the Hindi but question that need to ask to it, must be in English. He also so the assitant for the Arabic language. See the video for both.