Bingo; the Russians got there hands on a Nazi Sturmgewehr - 44 (the first assault rifle ever developed) and reworked it accordingly, three years later.
Actually, the AK has more in common with American designs, than German. For example, the AK’s trigger is similar to that of the Garand rifle. Also, it’s bolt is similar to the Garand’s and the M1 Carbine’s. Basically, Mikey T. was a more sophisticated borrowed.
Soviets had similar platforms long before WWII including fully-auto rifles (AVS-36). It has little to none in common with Sturmgewehr design-wise.
I think German rifle itself was inspired Soviet designs.
The real innovation in Sturmgevehr was a use of intermediate cartridge. It made fully-auto rifle any practical for the first time and Kalashnikov utilized this trend in a simple refined design.
It took many years for US military to get an idea.
M-14 has failed with US military the same way similar AVS-36 has failed and was finally rejected by the Red Army in mid-30s.
With Hugo Schmeisser on the design team of the AK-47...