STG 44 / MP43/44 rifles have been showing up all over the world in the last couple of years. An eagle-eyed reader spotted one at Ukraine’s newest and most popular tourist attraction, the private palace of their former President. The above image is a still from a VICE video (See 2:10. Embedded below) of the Presidents sprawling complex. Also take a look at his ammunition collection at 3:29.
Ukraine was invaded by Germany during WWII. Kiev was occupied from September 1941 until November 1943. It is possible this gun originated from the German occupation.
Thanks to Pablo for the tip.