Starting from the wpDiscuz 7.6.0 version, you can change the attributes of the wpDiscuz comment form using the wpdiscuz_comment_form_args hook.

With the hook, you'll be allowed to add the 'notranslate' class for the wpDiscuz comment form, so the GTranslate plugin functions won't work for the wpDiscuz comment form.

 You should use the hook code below: 

add_filter("wpdiscuz_comment_form_args", function($args){
    $args["class_form"][] = "notranslate";
    return $args;
});

This doc should help you easily add the PHP code in the active theme functions.php file: https://www.wpbeginner.com/plugins/how-to-easily-add-custom-code-in-wordpress-without-breaking-your-site/