You have it reversed, the Germans created the STG-44 first, he took ideas from the M-1 Garand and the STG-44 and built his own rifle - after the war I think in late 1946 it got redesigned as the earlier version wasn't very reliable.
I feel bad for the guy, you would think of the millions made he would be rich, I think he lived in a 1 bedroom apartment on barely any money in the past 15 years. Secondly he was haunted because the weapons "ease" of manufacture and sell, terrorist and everyone else uses it. One point he blamed politicians for this and they cut his retirement money, putting much leaving him poor.
I believe the Germans were the 'copiests'
The Russians were to first to basically develop all that the Germans had..albeit not literally.
case in point. FG42 which is similar to the BAR..but too heavy and with much recoil..just like the BAR.
after that you have the G43...design very much like the Russian SVT40 ie: full size cartridge and a 10rnd box mag.
but recoil in the SVT and the G43 was TREMENDOUS. and with a full size rifle..kinda unwieldy.
so with the introduction of the 7.92x33 Kurz M43 round in Germany, AND the 7.62x39 M43 in Russia, you
have the basis for development of 'intermediate' weapons to use.
So the Germans took the action from the SVT40 and put it in their MP43..yes people I typed 'MP' 43.
Hitler wasn't interested in nu rifles and anything with 'Gewehr' (means rifle) in it would rouse his ire.
but Adolf's radar was not aroused by MP weapons..so the CO that made the SG44, billed it as a MP (Machine Pistol) in its
development stages.
The Russian engineer, Siminov was hard at work before Kalashnikov and he developed the SKS45 rifle for the nu 7.62x39.
Kalashnikov had nothing but probs with the AK hence its adaption was delayed till 1947.
so Kalashnikov AK was not inspired by the SG.
considering the SVT, StG44 and SKS 'drop bolt', the AKs 'rotating bolt may have borrowed from the M1.
but then, since all 'bolts' rotate in rifles, (M1903, MosinNagant, K98, et al) it would not be a strench to keep that idea in mind
when developing a nu rifle.