http://www.newscientist.com/channel/life/mg18524825.800

Rats learn to distinguish between languages
15 January 2005
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THEY may not be noted for their linguistic skills, but it turns out
rats can learn the difference between Dutch and Japanese.
Juan Toro's team at the University of Barcelona in Spain trained rats
to press a lever when they heard Japanese, produced by a speech
synthesiser. Others were rewarded for responding to Dutch.
The rats trained to recognise Japanese did not respond to Dutch, and
vice versa (Journal of Experimental Psychology: Applied Behaviour Processes,
vol 31, p 95). They could not tell the difference if the sentences were
read backwards, however, which suggests that the animals distinguish them by
rhythmic patterns.

From issue 2482 of New Scientist magazine, 15 January 2005, page 18