title: i18n translation for "Back"-text in React Navigation on iOS
body: <p>I'm using <a href="https://reactnavigation.org/" rel="nofollow noreferrer">React Navigation</a> and a StackNavigator in a React Native app. I'm able to translate the <code>navigationOptions.title</code>, however, on iOS if there is too much text in the header it defaults to showing the text "Back" next to the back button. I don't mind this, but I want it to say "Back" in my current language. How can I achieve this? The text I'm talking about:</p>
  
  <p><a href="https://i.stack.imgur.com/Z6wl6.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Z6wl6.png" alt="Back button"></a></p>
  
  <p>An example of how I use the <code>navigationOptions</code> now:</p>
  
  <pre><code>class Example extends Component&lt;Props&gt; {
      static navigationOptions = () =&gt; ({
          title: i18n.t('example_title'),
      });
      // ...
  }
  </code></pre>
  
  <p>In case it is relevant we're using <a href="https://github.com/react-native-community/react-native-localize" rel="nofollow noreferrer"><code>react-native-localize</code></a> with <a href="https://github.com/fnando/i18n-js" rel="nofollow noreferrer"><code>i18n-js</code></a> for the i18n functionality. I don't want it to always say the previous screens name, or always back, I want it dynamically as it is now, just with i18n.</p>