The enrollment_action value enroll should not be translated.

lms/templates/courseware/course_about.html

@@ -219,10 +219,10 @@
     <form id="class_enroll_form" method="post" data-remote="true" action="${reverse('change_enrollment')}">
       <fieldset class="enroll_fieldset">
         <input name="course_id" type="hidden" value="${course.id}">
-        <input name="enrollment_action" type="hidden" value="${_("enroll")}">
+        <input name="enrollment_action" type="hidden" value="enroll">
       </fieldset>
       <div class="submit">
-        <input name="submit" type="submit" value="${_("enroll")}">
+        <input name="submit" type="submit" value="enroll">
       </div>
     </form>
   </div>