One you may not have heard of is "Watership Down" by Richard Adams. It's an off beat story of the life of rabbits. The author creates a rabbit culture and language.

Set in England's Downs, a once idyllic rural landscape, this stirring tale of adventure, courage and survival follows a band of very special creatures on their flight from the intrusion of man and the certain destruction of their home. Led by a stouthearted pair of friends, they journey forth from their native Sandleford Warren through the harrowing trials posed by predators and adversaries, to a mysterious promised land and a more perfect society.

I found it interesting because the author subtly teaches you Lapine as the story progresses. Near the end you understand when one of the characters says, "Silfrey hackura uh umbar Rah."