Voice prompts are the vocal cues produced by the headset, such as those to indicate when the headset is in pairing mode or how much battery time is remaining. If you like, you can switch these prompts off and replace them with less obtrusive 'beeps'.
To do so, first ensure that the headset is on but not in use (i.e. no active call or music reproduction). Now press and hold both volume buttons simultaneously for six seconds until you hear three chimes. To reactivate, simply follow the same steps.
Unfortunately, it is not possible to change the language of the voice prompts, only to disable them.