Hi,
1)How to add the contact form not in English?
Add a language in the block "Language settings for the field names in the form" on the plugin settings page.
Mark the check box (if it's not marked yet) in the block "Change the names of the contact form fields and error messages", choose the necessary tab and fill in the fields. Choose the necessary tab in the block "Action after email is sent" as well and fill in the field. Save the changes.
You will see the shortcode under the tab with the necessary language. Please paste that shortcode to the page or post.
2) It is not clear enough where exactly you add this line. Into some file? Why don't you use the standard method of adding a shortcode?
<?php echo do_shortcode('[contact_form lang=nb_NO]'); ?>
Sincerely,
Support Team