Can rats tell Dutch from Japanese?
Effects of backward speech and speaker variability in language discrimination by rats
Rats can tell Japanese from Dutch, but not when the sentences are played backwards.
Ig Nobel 2006
Rats were trained to respond to sentences in either Dutch or Japanese. They learned to tell the two languages apart by their rhythm.
When the sentences were played backwards, the rats could no longer tell them apart, which helps scientists figure out how human babies learn language.
Rats: bilingual-ish, but only forwards.