Password protected Page add_filter to change the text doesn’t work

I use the wordpress theme wpcasa and the theme change the standard text of wordpress.

So I included a filter hook of the theme:

add_filter( 'the_password_form', 'wpsight_password_form_dmd' );

function wpsight_password_form_dmd($output){
    global $post;
    $output="";
    $aktuelleseite = $_SERVER['REQUEST_URI'];
    $sprache = explode("https://wordpress.stackexchange.com/",$aktuelleseite);  


    $label="pwbox-".( empty( $post->ID ) ? rand() : $post->ID );

    $output="<form action="" . get_option( 'siteurl' ) . '/wp-login.php?action=postpass" method="post" class="form-password form-inline">';
    switch($sprache[1]){
        case 'en':
            $output .= '<p>Please include your password which we sent you.<br><br>You do not have a password? Than make a request <a href="https://wordpress.stackexchange.com/en/top-ten-request-form/"><u>here</u></a>.</p>';
            break;
        case 'de':
            $output .= '<p>Bitte geben Sie hier Ihr Passwort ein, welches wir Ihnen gesendet haben.<br><br>Sie haben kein Passwort? Dann fordern Sie <a href="http://wordpress.stackexchange.com/de/top-ten-zugangsformular/"><u>hier</u></a> eins an.</p>';
            break;
    }
    $output .= '    <label for="' . $label . '">' . __( 'Password', 'wpsight' ) . '<input name="post_password" id="' . $label . '" type="password" size="20" class="password span3" /></label><button type="submit" name="Submit" class="btn">' . esc_attr__( 'Submit', 'wpsight' ) . '</button></form>';

    return $output;    
}

Now it works everything fine.