In the novel Watership Down by Richard Adams, talking rabbits speak the constructed language Lapine as well as "hedgerow vernacular", a cross-species lingua franca.
This got me wondering what real-world languages to assign to other fictional anthropomorphic animals in order to provide a genius groan-us.
- Cats speak Catalan; those who speak Miao have been driven to the hills. In the real world, the .cat TLD has led to an expansion of information about Internet feline memes in Catalan.
- Common house pets with numerous breeds speak a variety of languages. German shepherd dogs speak German, Siamese cats speak Thai, Persian cats speak Farsi, cabbits speak Manx, etc.
- Frogs speak French.
- Geese speak Portuguese.
- Gerbils speak Dyirbal. In a story from gerbils' point of view, the avoidance language used when a cross in-law is present can be represented as ornate formal language.
- Turkeys speak Turkish because that's where they were domesticated. When turkeys say gobble gobble, they're actually saying "merhaba" which means hello.
- Invertebrates aren't left out: lice speak Lao.
- Fur itself can be used as a lingua franca.
- This is an incomplete list. Your puns are probably just as good as mine; suggest some on the talk page.