Saya rasa mula-mula anda menggunakan fungsi get_the_time untuk mendapatkan tarikh dan kemudian menukarnya kepada tarikh shamsi dan menggemakannya untuk paparan. Kod seperti di bawah berfungsi. Anda boleh menambah sebarang fungsi g2p lain yang anda mahukan.

add_filter('the_time', 'change_date_format');

function change_date_format(){
    //change date language here
    $date = get_the_time('Y/m/d');
    $date = explode('/', $date);
    $farsi_date = g2p($date[0],$date[1],$date[2]);
    return $farsi_date[0].'/'.$farsi_date[1].'/'.$farsi_date[2];
}

function g2p($g_y, $g_m, $g_d)
{
    $g_days_in_month = array(31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);
    $j_days_in_month = array(31, 31, 31, 31, 31, 31, 30, 30, 30, 30, 30, 29);

    $gy = $g_y-1600;
    $gm = $g_m-1;
    $gd = $g_d-1;

    $g_day_no = 365*$gy+floor(($gy+3)/4)-floor(($gy+99)/100)+floor(($gy+399)/400);

    for ($i=0; $i < $gm; ++$i){
        $g_day_no += $g_days_in_month[$i];
    }

    if ($gm>1 && (($gy%4==0 && $gy%100!=0) || ($gy%400==0))){
        /* leap and after Feb */
        ++$g_day_no;
    }

    $g_day_no += $gd;
    $j_day_no = $g_day_no-79;
    $j_np = floor($j_day_no/12053);
    $j_day_no %= 12053;
    $jy = 979+33*$j_np+4*floor($j_day_no/1461);
    $j_day_no %= 1461;

    if ($j_day_no >= 366) {
        $jy += floor(($j_day_no-1)/365);
        $j_day_no = ($j_day_no-1)%365;
    }
    $j_all_days = $j_day_no+1;

    for ($i = 0; $i < 11 && $j_day_no >= $j_days_in_month[$i]; ++$i) {
        $j_day_no -= $j_days_in_month[$i];
    }

    $jm = $i+1;
    $jd = $j_day_no+1;

    return array($jy, $jm, $jd, $j_all_days);
}