function sanitize_file_names_pix685894( $filename ){



  // Generate Array to retrieve file extension

  $fileArr = explode('.', $filename);



  // Get Fileextension by storing the last array element into new var

  $fileExt = array_values(array_slice( $fileArr, -1))[0];



  // delete the last element from array

  $newArr = array_pop( $fileArr );



  // rebuild filename WITHOUT the file extension

  $filename = implode('.', $fileArr);



  // remove all special chars from string

  $filename = preg_replace('/[^A-Za-z0-9\-]/', '', $filename);



  // WP function remove accents

  $filename = remove_accents( $filename );



  // WP function sanitize filename (remove spaces, etc...)

  $filename = sanitize_title( $filename );



  // add file extension

  $filename = $filename . '.' . $fileExt;



  // gogogo!

  return $filename;



}

add_filter('sanitize_file_name','sanitize_file_names_pix685894',10);