(PHP 4 >= 4.0.6, PHP 5)
mb_internal_encoding — Set/Get internal character encoding
Set/Get the internal character encoding
encoding
       encoding is the character encoding name 
       used for the HTTP input character encoding conversion, HTTP output 
       character encoding conversion, and the default character encoding 
       for string functions defined by the mbstring module.
       You should notice that the internal encoding is totally different from the one for multibyte regex.
      
   If encoding is set, then 
   Returns TRUE on success or FALSE on failure.
   In this case, the character encoding for multibyte regex is NOT changed.
   If encoding is omitted, then 
   the current character encoding name is returned.
  
Example #1 mb_internal_encoding() example
<?php
/* Set internal character encoding to UTF-8 */
mb_internal_encoding("UTF-8");
/* Display current internal character encoding */
echo mb_internal_encoding();
?>