
The first option is that Christian is himself involved with either Widmore or the Others and can travel through time. In that case, Christian as we have seen him in the last two episodes has travelled from some time in the past to this point in time.
The second option is that this is a manifestation of Christian in the same way he has been manifested to Jack, but these manifestations depend on a person’s memories, and since Christian has been manifesting to (and in connection with) Claire, it shouldn’t surprise us that he would look different. This is Christian as Claire remembers him.

One last thing to note. The Ottomans ruled North Africa at one point. When Ben appears in Tunisia and tries Turkish as well as Arabic, this doesn’t indicate that he could have travelled to any place, but simply that he was trying languages that might have been spoken there at different times.