// $available_languages
Array
(
    [0] => en
    [1] => zh-cn
    [2] => es
)
// $_SERVER["HTTP_ACCEPT_LANGUAGE"]
Array
(
    [0] => en-us
    [1] => en;q=0.8
    [2] => es-cl;q=0.5
    [3] => zh-cn;q=0.3
)
// Result
en