The description of the zone of truth spell says:
you create a magical zone that guards against deception
But later on, it says:
On a failed save, a creature can't speak a deliberate lie while in the radius.
Say a character casts zone of truth on a mute person, or perhaps the party trickster simultaneously casts silence in the same area.
Under the mechanics of zone of truth, can an affected creature lie using sign language or a non-vocal form of communication?