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functions.php ekleyin.

//sayfalamayi yazidan sonra yap
add_filter('wp_link_pages_args','add_next_and_number');
function add_next_and_number($args){
    if($args['next_or_number'] == 'next_and_number'){
        global $page, $numpages, $multipage, $more, $pagenow;
        $args['next_or_number'] = 'number';
        $prev = '';
        $next = '';
        if ( $multipage ) {
            if ( $more ) {
                $i = $page - 1;
                if ( $i && $more ) {
                    $prev .= _wp_link_page($i);
                    $prev .= $args['link_before']. $args['previouspagelink'] . $args['link_after'] . '</a>';
                }
                $i = $page + 1;
                if ( $i <= $numpages && $more ) {
                    $next .= _wp_link_page($i);
                    $next .= $args['link_before']. $args['nextpagelink'] . $args['link_after'] . '</a>';
                }
            }
        }
        $args['before'] = $args['before'].$prev;
        $args['after'] = $next.$args['after'];   
    }
    return $args;
}

add_filter ('the_content', 'pagination_after_post',1);
function pagination_after_post($content) {
   if(is_single()) {
   
		$argsayfala = array(
				'before' => '<div style="height:10px;"></div><div class="foto-galeri-sayfala" align="center">',
				'after' => '</div><div style="height:10px;"></div>',
				'link_before' => '<span>',
				'link_after' => '</span>',
				'next_or_number' => 'next_and_number',
				'nextpagelink' => __('İleri'),
				'previouspagelink' => __('Geri'),
				'pagelink' => '%',
				'echo' => 0 );
		
	$content.= wp_link_pages($argsayfala);
   }
   return $content;
}

//nextpage kodu shortcode
add_filter('mce_buttons','wysiwyg_editor');
function wysiwyg_editor($mce_buttons) {
    $pos = array_search('wp_more',$mce_buttons,true);
    if ($pos !== false) {
        $tmp_buttons = array_slice($mce_buttons, 0, $pos+1);
        $tmp_buttons[] = 'wp_page';
        $mce_buttons = array_merge($tmp_buttons, array_slice($mce_buttons, $pos+1));
    }
    return $mce_buttons;
}

style.css ekleyin

/* foto-galeri-sayfala */
	.foto-galeri-sayfala {margin-top:10px;overflow:hidden;font-family:open sans;}
		 .foto-galeri-sayfala a {padding:4px 7px;background:#ececec;border:1px solid #ddd;margin-right:5px;}
			.foto-galeri-sayfala a span {font-weight:700;}
		 .foto-galeri-sayfala a:hover {background:#333;color:#fff;}
			 .foto-galeri-sayfala > span {padding:4px 7px;font-weight:700;color:#fff;background:#2d80c4;border:1px solid #ddd;margin-right:5px;}

Son olarak yazı girerken resimlerin arasına koyun: <!--nextpage-->