Example of a React application using the react-intl library along with an external json-formatted messages file and it's spanish translated version. Gist: https://gist.github.com/zv3/804ea6da48d149ca9ddf583a7f9ab1a1

<!DOCTYPE html>
<html>
  <head>
    <script src="https://unpkg.com/react@15.3.2/dist/react.js"></script>
    <script src="https://unpkg.com/react-dom@15.3.2/dist/react-dom.js"></script>

    <script src="https://npmcdn.com/react-intl@2.1.5/dist/react-intl.min.js"></script>
    <script src="https://unpkg.com/react-intl@2.1.5/locale-data/es.js"></script>
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=Intl.~locale.es"></script>

    <script src="https://jspm.io/system@0.19.js"></script>
  </head>
  <body>
    <div id="root"></div>

    <script type="text/javascript">
      System.config({
        transpiler: 'babel',
        packages: {
          './': {
            defaultExtension: false
          },
        }
      });

      System
        .import('./script.jsx')
        .catch (console.error.bind(console));
    </script>
  </body>
</html>

const { IntlProvider, FormattedMessage, addLocaleData } = ReactIntl;

// Import your json file containing the default messages
import defaultMessages from './defaultMessages.json!json';

// Import your json file containing the translated messages,
// in this example we are importing the spanish version of our messages.
import spanishMessages from './messages_ES.json!json';

const { es } = ReactIntlLocaleData;
addLocaleData([...es]);

const App = () => (
  <IntlProvider locale="es" messages={spanishMessages}>
    <div>
      <FormattedMessage 
        // Pass the corresponding property from the defaultMessages object that was previously loaded in line 4, 
        // each property in the .json file needs to be defined using the 'Message Descriptor' signature/concept (https://github.com/yahoo/react-intl/wiki/API#message-descriptor)
        {...defaultMessages.headerStrings.title} 
      />
    </div>
  </IntlProvider>
);

ReactDOM.render(<App />, document.getElementById("root"));

{
  "headerStrings.title": "Titulo de la aplicación"
}

{
  "headerStrings": {
    "title": {
      "id": "headerStrings.title",
      "description": "Title of the app.",
      "defaultMessage": "Intl Company, Inc."
    }
  }
}