Added locale (english only at the moment) and modifed the EJS so I think

every string is customisable (via the /locales/selected locale)

views/posts/user.ejs

@@ -2,14 +2,15 @@
     <%= post.title %>
 </h3>
 <%- converter.makeHtml(post.content) %><br/>
-<a href="/post/<%- index %>">Permalink</a><br/>
+<a href="/post/<%- index %>"><%= locale.permalink %></a><br/>
+<br/>
 
 <!-- Comment form -->
 <form method="POST" action="/submit_comment">
     <input type="hidden" name="post_index" value="<%= index %>">
-    <input placeholder="username" name="name"><br/>
-    <textarea placeholder="comment" name="content"></textarea><br/>
-    <button type="submit">Submit</button>
+    <label><%= locale.username %>:</label><br/><input name="name"><br/><br/>
+    <label><%= locale.comment %>:</label><br/><textarea name="content"></textarea><br/>
+    <button type="submit"><%= locale.submit %></button>
 </form>
 
 <% comments[index].forEach((comment, index) => { %>