I would appreciate any reference that contains either a translation or proof of the main theorem in [this](http://www.numdam.org/item?id=BSMF_1955__83__279_0) paper. Thank you in advanced.



Marcel Berger's "Sur les groupes d'holonomie homogènes de variétés à connexion affine et des variétés riemanniennes."
Perhaps Robert Bryant's "[Recent advances in the theory of holonomy](http://www.numdam.org/item?id=SB_1998-1999__41__351_0)" would be a good place to start.


