AS I came from a country where we use the french system in defining the voltage current arrows in electronic circuit, I am confused about the German/Austrian system where I see the voltage arrow is directed from positive to negative and this makes me confused when it comes to analyse complex circuit especially with diodes and mosfet. any clarification is more than welcome
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.
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.