Update i18n pages to include predefined messages (e.g. @@bidi_dir)....

chrome/common/extensions/docs/static/i18n.html

 <div id="pageData-name" class="pageData">Internationalization (i18n)</div>
 
 <!--
 [NOTEs for editors:
  * Try to be consistent about string vs. message (it's probably not yet).
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 <p id="classSummary">
 An <em>internationalized</em> extension
@@ skipping 36 matching lines @@
 </p>
 
 <img src="images/i18n-before.gif"
  alt='A manifest.json file and a file with JavaScript. The .json file has "name": "Hello World". The JavaScript file has title = "Hello World";'
  width="323" height="148">
 
 <p>
 To internationalize this extension,
 you name each user-visible string
 and put it into a messages file.
-The extension's manifest and JavaScript code
+The extension's manifest,
+CSS files,
+and JavaScript code
 use each string's name to get its localized version.
 </p>
 
 <p>
 Here's what the extension looks like when it's internationalized
 (note that it still has only English strings):
 </p>
 
 <img src="images/i18n-after-1.gif"
  alt='In the manifest.json file, "Hello World" has been changed to "__MSG_extName__", and a new "default_locale" item has the value "en". In the JavaScript file, "Hello World" has been changed to chrome.i18n.getMessage("extName"). A new file named _locales/en/messages.json defines "extName".'
  width="782" height="228">
 
 <p class="note">
 <b>Important:</b>
 If an extension has a <code>_locales</code> directory,
 the <a href="manifest.html">manifest</a>
 <b>must</b> define "default_locale".
 </p>
 
 <p>
 Some notes about internationalizing extensions:
 </p>
 
 <ul>
   <li><p>
-    Use only <a href="#overview-locales">supported locales</a>!
+    You can use any of the <a href="#overview-locales">supported locales</a>.
+    If you use an unsupported locale,
+    Google Chrome ignores it.
   </p></li>
 
   <li>
-    In <code>manifest.json</code>,
+    In <code>manifest.json</code>
+    and CSS files,
     refer to a string named <em>messagename</em> like this:
     <pre>__MSG_<em>messagename</em>__</pre>
   </li>
 
   <li>
     In your extension's JavaScript code,
     refer to a string named <em>messagename</em>
     like this:
     <pre>chrome.i18n.getMessage("<em>messagename</em>")</pre>
 
   <li> <p>
     In each call to <code>getMessage()</code>,
     you can supply up to 9 strings
     to be included in the message.
     See <a href="#examples-getMessage">Examples: getMessage</a>
     for details.
     </p>
   </li>
 
+  <li><p>
+    Some messages, such as <code>@@bidi_dir</code> and <code>@@ui_locale</code>,
+    are provided by the internationalization system.
+    See the <a href="#overview-predefined">Predefined messages</a> section
+    for a full list of predefined message names.
+    </p>
+  </li>
+
   <li>
     In <code>messages.json</code>,
     each user-visible string has a name, a "message" item,
     and an optional "description" item.
     The name is a key
     such as "extName" or "search_string"
     that identifies the string.
     The "message" specifies
     the value of the string in this locale.
     The optional "description"
@@ skipping 27 matching lines @@
 under <code>_locales/es</code>.
 The following figure shows the previous extension
 with a new Spanish translation.
 </p>
 
 <img src="images/i18n-after-2.gif"
  alt='This looks the same as the previous figure, but with a new file at _locales/es/messages.json that contains a Spanish translation of the messages.'
  width="782" height="358">
 
 
+<h2 id="overview-predefined">Predefined messages</h2>
+
+<p>
+The internationalization system provides a few predefined
+messages to help you localize your extension.
+These include <code>@@ui_locale</code>,
+so you can detect the current UI locale,
+and a few <code>@@bidi_...</code> messages
+that let you detect the text direction.
+The latter messages have similar names to constants in the
+<a href="http://code.google.com/apis/gadgets/docs/i18n.html#BIDI">
+gadgets BIDI (bi-directional) API</a>.
+</p>
+
+<p>
+The special message <code>@@extension_id</code>
+can be used in the CSS and JavaScript files of any extension,
+whether or not the extension is localized.
+This message doesn't work in manifest files.
+</p>
+
+<p>
+The following table describes each predefined message.
+</p>
+
+<table>
+<tr>
+  <th>Message name</th> <th>Description</th>
+</tr>
+<tr>
+  <td> <code>@@extension_id</code> </td>
+  <td>The extension ID;
+    you might use this string to construct URLs
+    for resources inside the extension.
+    Even unlocalized extensions can use this message.
+    <br>
+    <b>Note:</b> You can't use this message in a manifest file.
+    </td>
+</tr>
+<tr>
+  <td> <code>@@ui_locale</code> </td>
+  <td>The current locale;
+    you might use this string to construct locale-specific URLs. </td>
+</tr>
+<tr>
+  <td> <code>@@bidi_dir</code> </td>
+  <td> The text direction for the current locale,
+       either "ltr" for left-to-right languages such as English
+       or "rtl" for right-to-left languages such as Japanese. </td>
+</tr>
+<tr>
+  <td> <code>@@bidi_reversed_dir</code> </td>
+  <td> If the <code>@@bidi_dir</code> is "ltr", then this is "rtl";
+       otherwise, it's "ltr". </td>
+</tr>
+<tr>
+  <td> <code>@@bidi_start_edge</code> </td>
+  <td> If the <code>@@bidi_dir</code> is "ltr", then this is "left";
+       otherwise, it's "right". </td>
+</tr>
+<tr>
+  <td> <code>@@bidi_end_edge</code> </td>
+  <td> If the <code>@@bidi_dir</code> is "ltr", then this is "right";
+       otherwise, it's "left". </td>
+</tr>
+</table>
+
+<p>
+Here's an example of using <code>@@extension_id</code> in a CSS file
+to construct a URL:
+</p>
+
+<pre>
+body {
+  <b>background-image:url('chrome-extension://__MSG_@@extension_id__/background.png');</b>
+}
+</pre>
+
+<p>
+If the extension ID is abcdefghijklmnopqrstuvwxyzabcdef,
+then the bold line in the previous code snippet becomes:
+</p>
+
+<pre>
+background-image:url('chrome-extension://abcdefghijklmnopqrstuvwxyzabcdef/background.png');
+</pre>
+
+<p>
+Here's an example of using <code>@@bidi_*</code> messages in a CSS file:
+</p>
+
+<pre>
+body {
+  <b>dir: __MSG_@@bidi_dir__;</b>
+}
+
+div#header {
+  margin-bottom: 1.05em;
+  overflow: hidden;
+  padding-bottom: 1.5em;
+  <b>padding-__MSG_@@bidi_start_edge__: 0;</b>
+  <b>padding-__MSG_@@bidi_end_edge__: 1.5em;</b>
+  position: relative;
+}
+</pre>
+
+<p>
+For left-to-right languages such as English,
+the bold lines become:
+</p>
+
+<pre>
+dir: ltr;
+padding-left: 0;
+padding-right: 1.5em;
+</pre>
+
+
 <h2 id="overview-locales">Locales</h2>
 
 <p>
 Extensions can use all the locales that Google Chrome supports,
 plus a few (such as <code>en</code>)
 that let a single translation support multiple variations of a language
 (such as <code>en_GB</code> and <code>en_US</code>).
 </p>
 
 
@@ skipping 280 matching lines @@
   })
 }
 </pre>
 
 <p>
 For details on calling <code>getAcceptLanguages()</code>, see the
 <a href="#method-getAcceptLanguages">API reference</a>.
 </p>
 
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