bitcoin-paper: Add Japanese Translation

_templates/bitcoin-paper.html

@@ -29,6 +29,15 @@ id: bitcoin-paper
           </b>
         </li>
 
+        <li class="card bitcoin-paper-card">
+          <img src="/img/flags/jp.svg?{{site.time | date: '%s'}}" alt="Japanese flag">
+          <a class="language-link" href="/files/bitcoin-paper/bitcoin_jp.pdf">日本語</a> 
+          <div>
+            <span>{% translate translated_by %}</span>
+            <a href="https://github.com/cryptohakka">hakka</a> 
+          </div>
+        </li> 
+
         <li class="card bitcoin-paper-card">
           <img src="/img/flags/id.svg?{{site.time | date: '%s'}}" alt="Indonesian flag">
           <a class="language-link" href="/files/bitcoin-paper/bitcoin_id.pdf">Bahasa Indonesia</a>