How to rename weekdays and months in date?

By default, php date() function return weekdays and months in English (days: Monday, Tuesday… months: January, February…). I wonder how to rename these values because my site is going to be in Croatian and i want Croatian date format.
If anyone remembers, in cafelog b2 (old blog script) it was resolved in config.php file. Weekdays were presented as list variable:

$weekday[0] = "Monday";
$weekday[1] = "Tuesday";
...

$month[0] = "January";
$month[1] = "Februry";
...

I need something like this:

$weekday[0] = "Ponedjeljak";
$weekday[1] = "Utorak";
...

$month[0] = "Sijecanj";
$month[1] = "Veljaca";
...

Also, i will use it later in calendar, so i will need only first letter or first 3 letters of these variables.
Thanks in forward!
Ile