Speaking with animals is an extraordinary ability possessed by both Rangers
and Druids. Through extensive study of the behaviors of animals, they are
capable of both understanding and, to some extent, communicating with
animals.
Due to their close relationship with life underground, gnomes also possess
this ability, albeit to a lesser extent.
* Communication with animals should be commensurate with their intelligence,
and thus generally quite basic, as most animals (indeed, almost all those
having animal as their primary language) do not possess the intellect for the
sort of detailed conversations one humanoid might have with another. If you
can't reasonably pantomime out what you want with simple gestures or sounds,
it's probably too complex for this tongue.