Write the php function get_requestor_preferred_language(), which gets the language of the user calling the page. It should return one of 
es
de
en
fr
zh
jp
and use en as a fallback if it is none of them
Sure, here is the function:


```php
/**
 * Returns the language of the user calling the page
 *
 * @return	$lang		Language of the user if in a white list (default en)
 *
 * @ref	https://stackoverflow.com/questions/3770513/detect-browser-language-in-php
 */
function get_requestor_preferred_language() {
    $lang = substr($_SERVER['HTTP_ACCEPT_LANGUAGE'], 0, 2);
    $acceptLang = [es, de, en, fr, zh, jp];
    $lang = in_array($lang, $acceptLang) ? $lang : en;
    return $lang;
}
```