puedes utilizar esta funcion:
Código PHP:
/**
* transformar fecha de ingles a castellano
*/
function date_es($f_cast) {
$f_cast=str_replace("Sunday","Domingo",$f_cast);
$f_cast=str_replace("Monday","Lunes",$f_cast);
$f_cast=str_replace("Tuesday","Martes",$f_cast);
$f_cast=str_replace("Wednesday","Miércoles",$f_cast);
$f_cast=str_replace("Thursday","Jueves",$f_cast);
$f_cast=str_replace("Friday","Viernes",$f_cast);
$f_cast=str_replace("Saturday","Sábado",$f_cast);
$f_cast=str_replace("January","Enero",$f_cast);
$f_cast=str_replace("February","Febrero",$f_cast);
$f_cast=str_replace("March","Marzo",$f_cast);
$f_cast=str_replace("April","Abril",$f_cast);
$f_cast=str_replace("May","Mayo",$f_cast);
$f_cast=str_replace("June","Junio",$f_cast);
$f_cast=str_replace("July","Julio",$f_cast);
$f_cast=str_replace("August","Agosto",$f_cast);
$f_cast=str_replace("September","Septiembre",$f_cast);
$f_cast=str_replace("October","Octubre",$f_cast);
$f_cast=str_replace("November","Noviembre",$f_cast);
$f_cast=str_replace("December","Diciembre",$f_cast);
return $f_cast;
}