Add chrome.i18n to the list of chrome.* APIs.

common/extensions/docs/static/api_index.html

 <div id="pageData-title" class="pageData">chrome.* APIs</div>
 
 <p>
 Google Chrome provides APIs such as
 <code>chrome.bookmarks</code> and <code>chrome.tab</code>
 so that extensions can interact with the browser.
 Here are the supported chrome.* APIs:
 </p>
 
 <ul>
   <li><a href="bookmarks.html">bookmarks</a></li>
   <li><a href="extension.html">extension</a></li>
+  <li><a href="i18n.html">i18n</a></li>
   <li><a href="pageActions.html">pageActions</a></li>
   <li><a href="tabs.html">tabs</a></li>
   <li><a href="toolstrip.html">toolstrip</a></li>
   <li><a href="windows.html">windows</a></li>
 </ul>
 
 <p>
 Unless the doc says otherwise,
 methods in the chrome.* APIs are asynchronous:
 they return immediately,
 without waiting for the operation to finish.
 If you need to know the outcome of an operation,
 then you pass a callback function into the method.
 <span class="comment">[PENDING: update/elaborate on that]</span>
 </p>