Socialism

highly modified to fit a country’s issues

Not "highly" but Marxism Leninism is the only version which had that build in, hence we have Socialism with Chinese Characterstics or Juche which are still both ML.

Classical Communism as by Marx and Engels is almost impossible to implement thanks to human nature.

You already responded to my main question, like someone who never read anything except Manifesto or probably not even manifesto, else you would know that Marx and Engels never given a ready blueprint for communism, they left that to the people who would implement it, because they weren't dogmatics unlike the bunch of proudhons, lassales etc. and that even during the Marx life his political stance was being refined by revolutionary events - the biggest one would be formulation of the dictatorship of the proletariat doctrine after Paris Commune.

human nature

human nature

human nature