hmm... if I ever to hear "another voice" that is not the one I know all my life, which tone or accent it would have? I tried imagine any, I couldn't... to begin with, to "imagine it" it already grants that is self made, that the voice is still there alone; if ever having to hear another voice there could be no way obliged necessity to be in this language probably, in this frequency, etc... 

The problematic as far as i know is there could not be a way to verify with flesh and bones about cases in other people where they claim they indeed can...