CodeIgniter Disallowed Key Characters

The problem is you are using characters not included in the standard Regex. Use this:

!preg_match("/^[a-z0-9\x{4e00}-\x{9fa5}\:\;\.\,\?\!\@\#\$%\^\*\"\~\'+=\\\ &_\/\.\[\]-\}\{]+$/iu", $str)

As per the comments (and personal experience) you should not modify they Input.php file — rather, you should create/use your own MY_Input.php as follows:

<?php

class MY_Input extends CI_Input {

    /**
     * Clean Keys
     *
     * This is a helper function. To prevent malicious users
     * from trying to exploit keys we make sure that keys are
     * only named with alpha-numeric text and a few other items.
     * 
     * Extended to allow: 
     *      - '.' (dot), 
     *      - '[' (open bracket),
     *      - ']' (close bracket)
     * 
     * @access  private
     * @param   string
     * @return  string
     */
    function _clean_input_keys($str) {
        // UPDATE: Now includes comprehensive Regex that can process escaped JSON
        if (!preg_match("/^[a-z0-9\:\;\.\,\?\!\@\#\$%\^\*\"\~\'+=\\\ &_\/\.\[\]-\}\{]+$/iu", $str)) {
            /**
             * Check for Development enviroment - Non-descriptive 
             * error so show me the string that caused the problem 
             */
            if (getenv('ENVIRONMENT') && getenv('ENVIRONMENT') == 'DEVELOPMENT') {
                var_dump($str);
            }
            exit('Disallowed Key Characters.');
        }

        // Clean UTF-8 if supported
        if (UTF8_ENABLED === TRUE) {
            $str = $this->uni->clean_string($str);
        }

        return $str;
    }

}

// /?/> /* Should never close php file - if you have a space after code, it can mess your life up */

---

++Chinese Character Support

// NOTE: \x{4e00}-\x{9fa5} = allow chinese characters
// NOTE: 'i' — case insensitive
// NOTE: 'u' — UTF-8 mode
if (!preg_match("/^[a-z0-9\x{4e00}-\x{9fa5}\:\;\.\,\?\!\@\#\$%\^\*\"\~\'+=\\\ &_\/\.\[\]-\}\{]+$/iu", $str) { ... }

// NOTE: When Chinese characters are provided in a URL, they are not 'really' there; the browser/OS
//   handles the copy/paste -> unicode conversion, eg:
//        一二三  -->  xn--4gqsa60b   
//   'punycode' converts these codes according to RFC 3492 and RFC 5891.
//   https://github.com/bestiejs/punycode.js ---  $ bower install punycode