move system_get_language_code into head.inc

src/www/head.inc

 <?php
 
+function system_get_language_code() {
+	global $config;
+
+	// a language code, as per [RFC3066]
+	$language = $config['system']['language'];
+	$code = str_replace("_", "-", $language);
+
+	if (empty($code))
+		$code = "en-US"; // Set default code.
+
+	return $code;
+}
+
+
 $g['theme'] = get_current_theme();
 
 $pagetitle = gentitle( $pgtitle );