FIX Step navigation buttons are not translatable

lang/en.yml

@@ -148,6 +148,8 @@ en:
       one: 'A Page Break'
       other: '{count} Page Breaks'
     SINGULARNAME: 'Page Break'
+    STEP_NEXT: Next
+    STEP_PREV: Prev
     STEP_TITLE: 'Page {page}'
     TITLE_FIRST: 'First Page'
   SilverStripe\UserForms\Model\EditableFormField\EditableLiteralField:

templates/SilverStripe/UserForms/Form/Includes/UserFormStepNav.ss

@@ -5,10 +5,14 @@
 			so the 'prev' and 'next' button are not used. These buttons are made visible via JavaScript.
 		--%>
 		<li class="step-button-wrapper" aria-hidden="true" style="display:none;">
-			<button class="step-button-prev">Prev</button>
+			<button class="step-button-prev">
+                <%t SilverStripe\\UserForms\\Model\\EditableFormField\\EditableFormStep.STEP_PREV "Prev" %>
+            </button>
 		</li>
 		<li class="step-button-wrapper" aria-hidden="true" style="display:none;">
-			<button class="step-button-next">Next</button>
+			<button class="step-button-next">
+                <%t SilverStripe\\UserForms\\Model\\EditableFormField\\EditableFormStep.STEP_NEXT "Next" %>
+            </button>
 		</li>
 
 		<% if $Actions %>
@@ -20,4 +24,4 @@
 		<% end_if %>
 
 	</ul>
-</nav>
+</nav>