Hard to tell, but interesting if true.
One of the most obvious screening tests for authenticity of any apparition is that it doesn’t violate the Church’s teaching. Now, I know very little of Medjugoje, so this isn’t an indictment of that apparition per se. However, given that the Church has constantly taught that general revelation ceased with the passing of the Apostles, it follows that any apparition claiming to provide revelation that is in any way binding on all Christians is a false apparition. Relevant to all, fine, but not binding.
Status of Medjugorje: http://en.wikipedia.org/wiki/Catholic_Church_response_to_the_Medjugorje_apparitions
Dubious doctrines of Medjugorje:
– September 13, 1981: Jesus is the Father – September 16, 1981: The visionaries don’t need to pray for themselves – August 31, 1982: Mary is not the Dispenser of all heavenly gifts