Remove the opening and closing php tags from your code and then replace it. Eg:
if(comments_open()){
echo "<div class='comment_container ".avia_layout_class('entry',false)." units $indent'>";
echo "<h3 class='miniheading'>".__('Ihr Gästebucheintrag','avia_framework')."</h3>";
echo "<span class='minitext'>".__('Ich freue mich auf Ihr Feedback!','avia_framework')."</span>";
$comments_args = array(
'title_reply'=>'Add your guestbook entry',
'label_submit'=>'Send your guestbook entry',
'comment_field' => '<p class="comment-form-comment"><label for="comment">Your message</label>
<textarea id="comment" name="comment"></textarea></p>'
);
comment_form($comments_args);
echo "</div>";
}
Regards,
Devin
works fine, thanks a lot for your help!