Moriendor writes in with
confirmation from a Deep Silver rep on their forums that
Temple of Air (we'll have to see exactly what the English title is in due course) is indeed the third
Risen 2 DLC, counting
Treasure Isle (preorder bonus DLC) and the CE special items. For German readers, Moriendor writes:
It has also been confirmed that the German special edition (not the CE but the more expensive SSE) is going to include that DLC via the "secret handwritten note" that is supposed to be included in the box and that was a mystery item until today.
More information.