While this is up for speculation, a Portuguese blog known as BlogdoiPhone has apparently gotten a hold of a “pre-GM” build of iOS 5.1 from a local carrier that contains two notable new features. One of them is to be expected, as it has been recently leaked by Siri herself: she will now be able to speak Japanese, on top of the three other languages that she already can (English, French, and German).
The other new feature in this leaked iOS 5.1 build is a new camera slider button on the lock screen, which previously only showed up after double clicking the home button, and which served as a button rather than a slider. Sliding upwards will bring up the camera app, just as it did in previous iOS versions, although now more conveniently without having to unlock the iDevice.
We’ll see if this turns out to be true (I don’t have any doubts, honestly) once iOS 5.1 is released, likely alongside the third-generation iPad. No dates have been confirmed as of yet, but sometime in March is looking like the most likely possibility.