I have a question;
when someone talks about another person as not being of God, and that he is going to hell for a belief,religion, etc. and he ends up being one of the chosen by God, could we be charged with bearing false witness on him?
So, I don't know what Christianity would say about this, because I don't know how they have chosen to interpret
ou pseudomartureseis kata tou plesion sou marturian pseudu (ου ψευδομαρτυρησεις κατα του πλησιον σου μαρτυριαν ψευδη
or
Non loqueris contra proximum tuum falsum testimonium, which are what is translated as "Thou shalt not bear false witness against thy neighbour."
But I can certainly say that the original Hebrew
lo ta'aneh b'reyechah eid shaker does not refer to mere gossip or even slander, but to perjuring oneself under oath in open court to the detriment of another.
And since one cannot be charged with perjury for expressing an unpleasant but unprovable and not illegal opinion under oath, then no, one could not be charged with bearing false witness for saying such things as you've described against another. However, I would think that one could be charged with violating the commandments not to spread malicious gossip against others, and to love one's fellow person as one loves oneself.