Change post date format to hebrew calendar

Disclaimer

This is not a complete answer, because I can’t really handle signs I don’t know. It should help to point you in the right direction.

My (basic) solution

Taken from StackExchange, I created this function for your functions.php:

function ArabicDate( $time = false ) {

    if ( $time === false ) {
        $time = current_time( 'timestamp' );
    }
    $months = array("Jan" => "يناير", "Feb" => "فبراير", "Mar" => "مارس", "Apr" => "أبريل", "May" => "مايو", "Jun" => "يونيو", "Jul" => "يوليو", "Aug" => "أغسطس", "Sep" => "سبتمبر", "Oct" => "أكتوبر", "Nov" => "نوفمبر", "Dec" => "ديسمبر");
    $your_date = date( 'y-m-d', $time ); // The Date calculated from the $time variable
    $en_month = date("M", $time );
    foreach ($months as $en => $ar) {
        if ($en == $en_month) { $ar_month = $ar; }
    }

    $find = array ("Sat", "Sun", "Mon", "Tue", "Wed" , "Thu", "Fri");
    $replace = array ("السبت", "الأحد", "الإثنين", "الثلاثاء", "الأربعاء", "الخميس", "الجمعة");
    $ar_day_format = date('D', $time); // The Current Day
    $ar_day = str_replace($find, $replace, $ar_day_format);

    $standard = array("0","1","2","3","4","5","6","7","8","9");
    $eastern_arabic_symbols = array("٠","١","٢","٣","٤","٥","٦","٧","٨","٩");

    // use this line to format your arabic date
    $current_date = $ar_day.' '.date( 'd', $time )."https://wordpress.stackexchange.com/".$ar_month."https://wordpress.stackexchange.com/".date( 'Y', $time );
    $arabic_date = str_replace($standard , $eastern_arabic_symbols , $current_date);

    return $arabic_date;

}

This is not the best solution, as you have to hardcode the timeformat for your arabic date. I would love to do better, but I have no idea how to confirm if the output of the signs is correct.

Change $ar_month to date( 'm', $time ) if you want the month to be numbers, not the month in text, for example.

Afterwards, you can filter your date function with this code:

add_filter( 'get_the_date', 'f711_convert_to_arabic_date', 10, 3 );
function f711_convert_to_arabic_date( $the_date, $d, $post ) {
    $posttime = strtotime( $post->post_date );
    return ArabicDate( $posttime );
}

Now your template tags ( get_the_date() and the_date() ) echo or return your Arabic Date.

If you want to use it in a template, just call echo ArabicDate() for the current time, or echo ArabicDate( $timestamp ) for any Arabic Date.