It's not a phonetic depiction of an exact accent but rather, a general impression of the difficulty of the various animals understanding each other.

Kehaar's accent always looked like eye dialect Scandinavian to me—Eugene O'Neill uses similar phonetics for the character of Olson in the Glencairn plays, for example, right down to p for b, v for w, d for th. His repeated agreement of "Ya, ya" helps with that impression, too.

(I could have sworn I'd left this comment last month, but apparently not.)