what is the German/Austrian nomenclature(Voltage and current direction) in electronic circuit?
I think you stumbled over a convention called Verbraucherzählpfeilsystem. It's pretty common in German EE conventions.

All items are treated as loads, regardless if they are loads (Verbraucher) or generators.







simulate this circuit &ndash; Schematic created using CircuitLab

This idea is you don't have to put the arrows on the schematic. You simply write Verbraucherzählpfeilsystem somewhere prominent, then write

$$I_g = -100A$$
$$I_l = 100A$$
$$U_g = U_l = 100V$$

and everyone agrees \$I_g\$ and \$U_g\$ belong to a generator, because \$I_g\cdot U_g\$ is negative.

You could also write Generatorzählpfeilsystem somewhere and use the exactly opposite definition. But that's not so common in German EE.



Also note German convention is using U instead of V for voltage identifiers to avoid confusion with the V unit symbol.