Şimdi dosyayı tam olarak buldum.Tam olarak yapmam gereken nedir? urldecode,urlencode için...

İçeriği ise şu şekilde;

<?php
/*
Plugin Name: Nice Search
Version: 0.5
Plugin URI: http://txfx.net/wordpress-plugins/nice-search/
Description: Redirects ?s=query searches to /search/query, and converts %20 to +
Author: Mark Jaquith
Author URI: http://coveredwebservices.com/
*/

function cws_nice_search_redirect() {
	global $wp_rewrite;
	if ( !isset( $wp_rewrite ) || !is_object( $wp_rewrite ) || !$wp_rewrite->using_permalinks() )
		return;

	$search_base = $wp_rewrite->search_base;
	if ( is_search() && !is_admin() && strpos( $_SERVER['REQUEST_URI'], "/{$search_base}/" ) === false ) {
		wp_redirect( home_url( "/{$search_base}/" . urlencode( get_query_var( 's' ) ) ) );
		exit();
	}
}

add_action( 'template_redirect', 'cws_nice_search_redirect' );

// Hotfix for http://core.trac.wordpress.org/ticket/13961 for WP versions less than 3.5
if ( version_compare( $wp_version, '3.5', '<=' ) ) {
	function cws_nice_search_urldecode_hotfix( $q ) {
		if ( $q->get( 's' ) && empty( $_GET['s'] ) && is_main_query() )
			$q->set( 's', urldecode( $q->get( 's' ) ) );
	}
	add_action( 'pre_get_posts', 'cws_nice_search_urldecode_hotfix' );