Unusual characters not loaded in Boost static cache

(Setup: Drupal 6.20, Boost 1.18, Nginx 0.7.67)

When the URL of the boosted node contain character → or 中国新闻网新闻中心, the cached node is correctly cached in the cache directory, and correctly reflecting the URL.

But when accessing the node, the uncached node loaded instead.

Below is the Nginx rules I use:

server {
    server_name *.com *.net *.org;
    location / {
        root   /var/www/html/$host;
        index  index.php;
        set $boost "";
        set $boost_query "_";
        if ( $request_method = GET ) {
          set $boost G;
        }
        if ($http_cookie !~ "DRUPAL_UID") {
          set $boost "${boost}D";
        }
        if ($query_string = "") {
          set $boost "${boost}Q";
        }  
        if ( -f $document_root/cache/normal/$host$request_uri$boost_query.html ) {
          set $boost "${boost}F";
        }
        if ($boost = GDQF){
          rewrite ^.*$ /cache/normal/$host/$request_uri$boost_query.html break;
        } 
        if (!-e $request_filename) {
          rewrite  ^/(.*)$  /index.php?q=$1  last;
          break;
        }
    }
    location ~ \.php$ {
            fastcgi_pass    127.0.0.1:9000;
            fastcgi_index   index.php;
            fastcgi_param   SCRIPT_FILENAME /var/www/html/$host$fastcgi_script_name;
            include         fastcgi_params;
    }
}

I've tried adding charset utf-8; under http { and under server {. Both of them not works.

Since cached node is correctly created in the cache directory, so this is not Drupal or Boost problem, but the problem is how to make Nginx read that cached file.