Add string (not store code) to url

I want to add string to the end of url, but not the store code.
Example: I go to site.com/store_code, i want to replace the store code to my own string.
(because store_code has to be unique).

I enable the option on system -> web -> url option.
And change the code here :

    /**
 * Add store code to url in case if it is enabled in configuration
 *
 * @param   string $url
 * @return  string
 */
protected function _updatePathUseStoreView($url)
{
    if ($this->isUseStoreInUrl()) {
        $url .= $this->getCode() . '/';
    }
    return $url;
}

by

  /**
 * Add store code to url in case if it is enabled in configuration
 *
 * @param   string $url
 * @return  string
 */
protected function _updatePathUseStoreView($url)
{
    if ($this->isUseStoreInUrl()) {
        $url .= 'fr' . '/';
    }
    return $url;
}

it’s work except that the /fr is read like a part of an action controller and not the base url.

So the url ‘site.com/fr/customer/account’ return a 404.

I didn’t find how change this comportement.
Someone can help me ?

Thanks