frameworks_base/docs/html/guide/topics/resources/multilingual-support.jd

page.title=Language and Locale
page.tags=androidn
page.image=images/cards/card-nyc_2x.jpg

@jd:body

<div id="qv-wrapper">
<div id="qv">
<h2>In this document:</h2>
<ol>
	  <li><a href="#preN">Challenges in Resolving Language Resources</a></li>
    <li><a href="#postN">Improvements to Resource-Resolution Strategy</a></li>
    <li><a href="#design">Designing your App to Support Additional
      Locales</a></li>

</ol>

</div>
</div>

<p>Starting in Android 7.0 (API level 24),
Android provides enhanced support for multilingual users,
allowing them to select multiple locales in settings. Android
provides this capability by greatly expanding the number of locales supported
and changing the way the system resolves resources.</p>

<p>This document starts by explaining the resource resolution strategy in
versions of Android lower than 7.0 (API level 24). Next, it describes
the improved resource-resolution strategy in Android 7.0.
Last, it explains how to take advantage of
the expanded number of locales to support more multilingual users.</p>

<h2 id="preN">Challenges in Resolving Language Resources</h2>

<p>Prior to Android 7.0, Android could not always successfully
 match app and system locales.</p>

 <p>For example, assume that you have the following situation:</p>
 <ul>
 <li>Your app's default language is {@code en_US} (US English), and it also has
  Spanish strings localized in {@code es_ES}
  resource files.</li>
 <li> A device is set to {@code es_MX} </li>

<p>When your Java code refers to strings, the system would load
strings from the default ({@code en_US}) resource file, even if the app has
Spanish resources localized under {@code es_ES}. This is because when the system
 cannot find an exact match, it continues to look for resources by stripping the
 country code off the locale. Finally, if no match is found, the system falls
 back to the default, which is {@code en_US}. </p>


<p>The system would also default to {@code en_US} if the user chose a language that
the app didn't support at all, like French. For example:</p>

<p class="table-caption" id="t-resource-res">
<strong>Table 1.</strong> Resource resolution without an exact locale match.
</p>
<table>
<tbody>
<tr>
<th>User Settings</th>
<th>App Resources</th>
<th>Resource Resolution</th>
</tr>
<tr>
<td>fr_CH</td>
<td>
default (en)<br>
de_DE<br>
es_ES<br>
fr_FR<br>
it_IT<br>
</td>
 <td>
Try fr_CH =&gt; Fail<br>
Try fr =&gt; Fail<br>
Use default (en)
</td>
 </tr>
 </tbody>
</table>


<p>In this example, the system displays English strings without
knowing whether the user can understand English. This behavior is pretty common
today.</p>

<h2 id="postN">Improvements to Resource-Resolution Strategy</h2>
<p>Android 7.0 (API level 24) brings more robust resource resolution, and
 finds better fallbacks automatically.
 However, to speed up resolution and improve
 maintainability, you should store resources in the most common parent dialect.
 For example, if you were storing Spanish resources
 in the {@code values-es-rUS} directory
 before, move them into the {@code values-b+es+419} directory,
 which contains Latin American Spanish.
 Similarly, if you have resource strings in a
 directory named {@code values-en-rGB}, rename
 the directory to {@code values-b+en+001} (International
 English), because the most common
 parent for <code>en-GB</code> strings is {@code en-001}.
 The following examples explain why these practices improve performance and
reliability of resource resolution.</p>

<h3>Resource resolution examples</h3>

<p>With versions of Android greater than 7.0, the case described in
	<strong>Table 1</strong> is resolved differently:</p>

<p class="table-caption" id="t-improved-res">
<strong>Table 2.</strong> An improved resolution strategy for when there is no
exact locale match.</p>
<table>
<tr>
<th>User Settings</th>
<th>App Resources</th>
<th>Resource Resolution</th>
</tr>
<tr>
<td><ol>
<li> fr_CH</li>
</ol>
</td>
<td>
default (en)<br>
de_DE<br>
es_ES<br>
fr_FR<br>
it_IT<br>
</td>
<td>
Try fr_CH =&gt; Fail<br>
Try fr =&gt; Fail<br>
Try children of fr =&gt; fr_FR<br>
Use fr_FR
</td>
</tr>

</table>


<p>Now the user gets French resources instead of English. This example also shows
 why you should store French strings in {@code fr} rather than {@code fr_FR}
 for Android 7.0 or higher. Here the course of action is
 to match the closest parent dialect,
 making resolution faster and more predictable.</p>

<p>In addition to this improved resolution logic, Android now offers more
 user languages to choose from. Let’s try the above example again with Italian
 specified as an additional user language, but without app support for French.  </p>

<p class="table-caption" id="t-2d-choice">
<strong>Table 3.</strong> Resource resolution when the app only matches the
user's second-preferred locale setting.</p>
<table>
<tr>
<th>User Settings</th>
<th>App Resources</th>
<th>Resource Resolution</th>

</tr>
<tr>
<td><ol>
<li> fr_CH</li>
<li> it_CH</li>
</ol>
</td>
<td>
default (en)<br>
de_DE<br>
es_ES<br>
it_IT<br>
</td>
<td>
Try fr_CH =&gt; Fail<br>
Try fr =&gt; Fail<br>
Try children of fr =&gt; Fail<br>
Try it_CH =&gt; Fail<br>
Try it =&gt; Fail<br>
Try children of it =&gt; it_IT<br>
Use it_IT
</td>

</tr>

</table>
<p>
  The user still gets a language they understand, even though the app doesn’t
  support French.
</p>


<h2 id="design">Designing your App to Support Additional Locales</h2>
<h3>LocaleList API</h3>

<p>
  Starting with Android 7.0 (API level 24), Android exposes the
  {@code LocaleList.getDefault()} API
  that lets apps directly query the list of languages a user has specified. This API
  allows you to create more sophisticated
  app behavior and better-optimized display of content. For example, Search
  can show results in multiple languages based on user’s settings.  Browser apps
  can avoid offering to translate pages in a language the user already knows,
  and keyboard apps can auto-enable all appropriate layouts.
</p>

<h3>Formatters</h3>

<p>
  Up through Android 6.0 (API level 23), Android supported only one or
  two locales
  for many common languages
  (en, es, ar, fr, ru). Because there were only a few variants of each language,
  apps could get away with storing some numbers and dates as hard coded strings
  in resource files.  However, with Android's broadened set of supported
  locales, there can be
  significant differences in formats for dates, times, currencies, and similar
  information even within a single locale. Hard-coding your formats can produce
  a confusing experience for end users.
  Therefore, when developing for Android 7.0 or higher versions,
  make sure to use formatters instead of hard coding numbers and date strings.</p>

<p>
  For example, Android 7.0 and higher includes support for
  27 Arabic locales. These locales can share most resources,
  but some prefer ASCII digits, while others prefer native digits. For example,
  when you want to create a sentence with a digit variable, such as
  "Choose a 4 digit pin", use formatters as shown below:
</p>

<pre> format(locale, "Choose a %d-digit PIN", 4)</pre>