East German, and possibly one of the many thousand handguns captured by the Soviets during WWII and repatriated and put to use later in various roles.
The finish looks to have been redone with little or no prep (you can see nicks that were just reblued) -- a lot like the two Soviet-captured guns (Lugers) I once owned. (Both were all-matching except for the side plate.)
The Soviets seemed to not waste any time on good looks when refinishing those captured weapons...