trying to apply patch 22363.8 as a plugin to not mess with wp core files -helps me as well to understand the remove_ process ----do not use as it is not yet functioning -- getting 'fatal error: cannot redeclare...'

file-name-sanvertwo.php

<?php
/*
Plugin Name: file name sanitizer
Description: Removes accents at file upload from WP Trac. Patch at http://core.trac.wordpress.org/attachment/ticket/22363/22363.8.patch
Version: 26 10 2013
*/

remove_filter('sanitize_file_name', $filename, $filename_raw);

/**
* Start of Patch 22363.8
*
* Sanitizes a filename, replacing whitespace and illegal characters with dashes.
* Replaces all non-alphabetical, non-decimal characters (including 
* spaces) with dashes. Strips HTML tags and sanitizes HTML entities. Munges 
* extraneous file extensions with underscores. Converts the filenames to lowercase 
* when possible. 
* 
* If the PCRE UTF-8 extension is available, this function converts all characters 
* that don't have the Unicode property "Letter" or "Decimal number" to dashes. 
* 
* @since 2.1.0 
* 
* @param string $filename The filename to be sanitized
* @return string The sanitized filename
*/

function sanitize_file_name( $filename ) { 
       $filename_raw = $filename; 
	 
	    // Check if PCRE UTF-8 extension is compiled and working. 
	    static $pcre_utf8 = null; 
	    if ( is_null( $pcre_utf8 ) ) 
               $pcre_utf8 = ( 1 === @preg_match( '`[\p{L}]`u', "\xc3\xa0" ) ); // Try to match "latin small letter a with grave". Returns (int) 1 or (boolean) false. 
 
	    $encoding = seems_utf8( $filename ) ? 'UTF-8' : bloginfo( 'charset' ); 
	    $utf8_modifier = ( $pcre_utf8 && 'UTF-8' == $encoding ) ? 'u' : ''; 
  
 	    $filename = wp_strip_all_tags( $filename ); 
 	 
 	    // Decode all HTML entities available in current encoding and strip the rest 
 	    $filename = html_entity_decode( $filename, ENT_QUOTES, $encoding ); 
 	    $filename = preg_replace( "`&[a-zA-Z]{2,8};`$utf8_modifier", '', $filename );  
	        
	    // Apply filters before sanitizing to allow custom replacements 
	    $filename = apply_filters('sanitize_file_name', $filename, $filename_raw); 
	        
		// Convert illegal characters to dashes 
	    $special_chars = array("?", "[", "]", "/", "\\", "=", "<", ">", ":", ";", ",", "'", "\"", "&", "$", "#", "*", "(", ")", "|", "~", "`", "!", "{", "}", chr(0)); 
	    $special_chars = apply_filters('sanitize_file_name_chars', $special_chars, $filename_raw);
		$strip_characters = preg_quote( implode( '', $special_chars ), '`' ); 
 	    $filename = preg_replace( "`[$strip_characters]`$utf8_modifier", '-', $filename ); 
 
 	    if ( $pcre_utf8 ) { 
 		        // Convert everything except letters, decimal numbers, and "." (dot) to dashes if the PCRE UTF-8 extension is available 
 		        $filename = preg_replace( "`(?!\.)[^\p{L}\p{Nd}]+`$utf8_modifier", '-', $filename ); 
 		        if ( ! $filename ) // Invalid UTF-8 string or empty 
						return ''; 
 		} 
 		 
 		$filename = preg_replace( "`[\s-]+`$utf8_modifier", '-', $filename ); // Check whitespace and multiple dashes 
 		$filename = preg_replace( "`-\.`$utf8_modifier", '.', $filename );  // Trim dashes before a dot 
 		$filename = trim( $filename, '.-_' ); 
 		 
 		if ( function_exists( 'mb_strtolower' ) ) 
 		            $filename = mb_strtolower( $filename, mb_detect_encoding( $filename ) ); 
 		else if ( ! preg_match( '/[^\x20-\x7f]/', $string ) ) // Only ASCII characters present 
 		        $filename = strtolower( $filename ); 
 		 
	    // Split the filename into a base and extension[s] 
	    $parts = explode('.', $filename); 
	 
	    // Return if only one extension 
	    if ( count($parts) <= 2 ) 
				return $filename; 
	 
        // Process multiple extensions 
	    $filename = array_shift($parts); 
		$extension = array_pop($parts);
        $mimes = get_allowed_mime_types();

        // Loop over any intermediate extensions. Munge them with a trailing underscore if they are a 2 - 5 character
        // long alpha string not in the extension whitelist.			
	    foreach ( (array) $parts as $part) { 
	            $filename .= '.' . $part; 
		                
				if ( preg_match("`^[a-zA-Z]{2,5}\d?$`$utf8_modifier", $part) ) { 
                        $allowed = false; 
						foreach ( $mimes as $ext_preg => $mime_match ) { 
								$ext_preg = "`^($ext_preg)$`i$utf8_modifier"; 
								if ( preg_match( $ext_preg, $part ) ) { 	       
										$allowed = true; 
										break; 
								}
                        }
                        if ( !$allowed )
                                $filename .= '_';
                }
        }
        $filename .= '.' . $extension; 

		return $filename; 
} 
 
add_filter('sanitize_file_name', 'remove_accents' );
?>