Skift sprog?

Hej

Hvorfor kan jeg ikke få denne kode til at virke?
Den vil kun include danish.php


if ($_POST['language_change'] == 'danish') {
    $_SESSION['language'] = 'danish';
} elseif ($_POST['language_change'] == 'english') {
    $_SESSION['language'] = 'english';
} else {
    $_SESSION['language'] = 'english';
}

if ($_SESSION['language'] = 'danish') {
    require_once($_SERVER['DOCUMENT_ROOT'] . '/language/danish.php');
}elseif ($_SESSION['language'] = 'english') {
    require_once($_SERVER['DOCUMENT_ROOT'] . '/language/english.php');
} else {
    require_once($_SERVER['DOCUMENT_ROOT'] . '/language/english.php');
}

Form:

            <form action="index.php" method="post" style="float: right;">
            <span class="text">Select language:</span>&nbsp;<select name="language_change" onchange="this.form.submit()">
            <option value="danish">Danish</option>
            <option value="english">English</option>
            </select>
            <noscript><input type="submit" value="change" /></noscript>
            </form>