Du vash misht. Du vask misht. Grushdeva du kalt misht
The voices were what the Keeper of the underworld used to try and sway the Pristinely ungifted to aid him in escaping the underworld. Often he would choose those who were close to Richard Rahl, as he was the one that would always thwart the Keeper's attempts, or those with the correct mentality. Only the one that was chosen to be the Keeper's gateway into the world of life heard the language of the underworld. Others would merely be tools to aid the chosen.
Ones who heard the voices
Jennsen Rahl (the Keeper's chosen)