PHP: check browser default language

check-default-lang.php

<?php

function prefered_language( $available_languages, $http_accept_language = 'auto' ) {
	if ( 'auto' == $http_accept_language ) {
		// $http_accept_language = $_SERVER['HTTP_ACCEPT_LANGUAGE'];
		$http_accept_language = isset( $_SERVER['HTTP_ACCEPT_LANGUAGE'] ) ? $_SERVER['HTTP_ACCEPT_LANGUAGE'] : '';
	}
	preg_match_all( '/([[:alpha:]]{1,8})(-([[:alpha:]|-]{1,8}))?' . '(\s*;\s*q\s*=\s*(1\.0{0,3}|0\.\d{0,3}))?\s*(,|$)/i', $http_accept_language, $hits, PREG_SET_ORDER );

	$bestlang = $available_languages[0];
	$bestqval = 0;

	foreach ( $hits as $arr ) {
		$langprefix = strtolower( $arr[1] );
		if ( ! empty( $arr[3] ) ) {
			$langrange = strtolower( $arr[3] );
			$language = $langprefix . '-' . $langrange;
		} else {
			$language = $langprefix;
		}
		$qvalue = 1.0;
		if ( ! empty( $arr[5] ) ) {
			$qvalue = floatval( $arr[5] );
		}

		if ( in_array( $language, $available_languages ) && ( $qvalue > $bestqval ) ) {
			$bestlang = $language;
			$bestqval = $qvalue;
		} else if ( in_array( $langprefix, $available_languages ) && ( ( $qvalue * 0.9 ) > $bestqval ) ) {
			$bestlang = $langprefix;
			$bestqval = $qvalue * 0.9;
		}
	}
	return $bestlang;
}

if ( isset( $_GET['lang'] ) ) {
	$language = $_GET['lang'];
} else {
	$language = prefered_language( array( 'en', 'pt' ) );
}

?>