Back to the original question:
what are the differences between Xara Xtreme and MAGIX Xtreme Photo & Graphic Designer?

I just checked with Xara Group. Most important difference is that Magix' Xtreme is available in several languages: German, French, Italian, Spanish and Dutch.
Apart from that the start-up splash screen in MAGIX Xtreme has some adjustable options. And MAGIX' Xtreme comes with a little utility ("Face perfector"?) that Xara Xtreme doesn't have.