The STG 44 and AK-47 almost have nothing in common besides being assault rifles. The AK stole more from the M1 Garand than the STG 44. And even then it isn't a blatant copy as the AK is magazine fed, easier to field strip and has different sights etc.
Rifle Paternity Test: Pinning Down The M1 Garand's Influence On The AK -
What rifle influenced Kalashnikov’s famous carbine design more, the Garand M1, or the Haenel MP 43? This question was broached by blogger Jeff of TwistRate in a video posted to the Full30 gun video hosting website recently. Readers can follow the link to watch that video before reading my...www.thefirearmblog.com
The one thing I've heard which seems plausible though I have no evidence is that the Soviets used Nazi engineers to help the with the stamping technology for the AKM as they Soviets only had experience making stamped SMGs while the Nazis stamped the STG 44, MG 42 and parts for the K98.
Not every German was a Nazi you know.
Or do you?