Faulty date format

Hi,
i have an issue with the expiration date for patrons and the publish date for books: The standard format which is added in the form (eg. ?Dez/23/2013? seems to be outdated as upon saving i always get an error message like ?Invalid Expiration date (Dez/23/2013): illegal month (Dez). Should be one of jan, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec.?
Not such a big issue, but inconvenient.

Regards,
— O

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