Philip "Bluesmoon" Tellis has posted a tiny (under 3K minified) JavaScript library to format dates, inspired by PHP's strftime()
Examples:
d.strftime('%Y/%m/%d') » en: 2008/04/25 » fr: 2008/04/25 » de: 2008/04/25 d.strftime('%A, %d %B') » en: Friday, 25 April » fr: Vendredi, 25 Avril » de: Freitag, 25 April
There's also a demo to fiddle with.
I've previously had fun with kinda like the opposite: translating human-readable times into JS Date objects. Also here and here you have strtotime() look-alikes that take human-readable dates and turn them into Date objects.