I thinking that if you will be interested to include period of first german-soviet cooperation in 1929-1933 (blue OOB) and tanks tested in Panzerschule Kama during that time. Meaby that is some period when german Reichswehr tank program and soviet has some mutual development.
Kama Testing ground
https://en.wikipedia.org/wiki/Kama_tank_school
and tank in question will be
Leichttraktor
https://en.wikipedia.org/wiki/Leichttraktor
https://warspot.net/128-krupp-leichttraktor
There was also modernised variant with christie suspension meaby close to WW2 when was used as a training tank in Germany
Secound one was
Grostraktor
https://weaponsandwarfare.com/2018/0...e-grostraktor/
And soviet-german joint-venture developed by German engineer
Tank Grotte
