HTTP_ACCEPT_LANGUAGEをパースする関数

<?php
$cases = array(
	'ja',
	'ja-jp',
	'ja;q=1',
	'da, en-gb;q=0.8, en;q=0.7',
);

foreach ( $cases as $case )
{
	$acceptLanguages = parse_accept_language($case);
	echo 'CASE: '.$case.PHP_EOL;
	var_dump($acceptLanguages);
}

function parse_accept_language($acceptLanguage)
{
	preg_match_all('/(?P<langcode>[a-z-]+)(?:;q=(?P<quality>[0-9\.]+))?/', $acceptLanguage, $matches);

	foreach ( $matches['quality'] as &$quality )
	{
		if ( $quality === '' )
		{
			$quality = 1.0;
		}
		else
		{
			$quality = floatval($quality);
		}
	}

	$acceptLanguages = array_combine($matches['langcode'], $matches['quality']);

	return $acceptLanguages;
}

結果

CASE: ja
array(1) {
  ["ja"]=>
  float(1)
}
CASE: ja-jp
array(1) {
  ["ja-jp"]=>
  float(1)
}
CASE: ja;q=1
array(1) {
  ["ja"]=>
  float(1)
}
CASE: da, en-gb;q=0.8, en;q=0.7
array(3) {
  ["da"]=>
  float(1)
  ["en-gb"]=>
  float(0.8)
  ["en"]=>
  float(0.7)
}