Vulcan/packages/vulcan-core/lib/modules/components/App.jsx

import { Components, registerComponent, getSetting, Strings, runCallbacks, detectLocale } from 'meteor/vulcan:lib';
import React, { PureComponent } from 'react';
import PropTypes from 'prop-types';
import { IntlProvider, intlShape } from 'meteor/vulcan:i18n';
import withCurrentUser from '../containers/withCurrentUser.js';
import withEdit from '../containers/withEdit.js';

class App extends PureComponent {
  constructor(props) {
    super(props);
    if (props.currentUser) {
      runCallbacks('events.identify', props.currentUser);
    }
    this.state = {
      locale: this.initLocale(),
    };
  }

  initLocale = () => {
    let userLocale = '';
    const { currentUser, cookies } = this.props;
    const availableLocales = Object.keys(Strings);

    if (currentUser && currentUser.locale) {
      // 1. if user is logged in, check for their preferred locale
      userLocale = currentUser;
    } else if (cookies && cookies.get('locale')) {
      // 2. else, look for a cookie
      userLocale = cookies.get('locale');
    } else if (detectLocale()) {
      // 3. else, check for browser settings
      userLocale = detectLocale();
    }
    // if user locale is available, use it; else compare first two chars
    // of user locale with first two chars of available locales
    const availableLocale = Strings[userLocale] ? userLocale : availableLocales.find(locale => locale.slice(0,2) === userLocale.slice(0,2));

    // 4. if user-defined locale is available, use it; else default to setting or `en-US`
    return availableLocale ? availableLocale : getSetting('locale', 'en-US');
  };

  getLocale = (truncate = false) => {
    return truncate ? this.state.locale.slice(0,2) : this.state.locale;
  };

  setLocale = locale => {
    this.setState({ locale });
    // if user is logged in, change their `locale` profile property
    if (this.props.currentUser) {
     this.props.editMutation({ documentId: this.props.currentUser._id, set: { locale }});
    }
  };

  getChildContext() {
    const messages = Strings[this.getLocale()] || {};
    const intlProvider = new IntlProvider({ locale: this.getLocale() }, messages);
    const { intl } = intlProvider.getChildContext();
    return {
      intl: intl,
      getLocale: this.getLocale,
      setLocale: this.setLocale,
    };
  }

  componentWillUpdate(nextProps) {
    if (!this.props.currentUser && nextProps.currentUser) {
      runCallbacks('events.identify', nextProps.currentUser);
    }
  }

  render() {
    const currentRoute = _.last(this.props.routes);
    const LayoutComponent = currentRoute.layoutName
      ? Components[currentRoute.layoutName]
      : Components.Layout;

    return (
      <IntlProvider
        locale={this.getLocale()}
        messages={Strings[this.getLocale()]}
      >
        <div className={`locale-${this.getLocale()}`}>
          <Components.HeadTags />
          <Components.RouterHook currentRoute={currentRoute} />
          <LayoutComponent {...this.props} currentRoute={currentRoute}>
            {this.props.currentUserLoading ? (
              <Components.Loading />
            ) : this.props.children ? (
              this.props.children
            ) : (
              <Components.Welcome />
            )}
          </LayoutComponent>
        </div>
      </IntlProvider>
    );
  }
}

App.propTypes = {
  currentUserLoading: PropTypes.bool,
};

App.childContextTypes = {
  intl: intlShape,
  setLocale: PropTypes.func,
  getLocale: PropTypes.func,
};

App.displayName = 'App';

const editOptions = {
  collectionName: 'Users',
  fragmentName: 'UsersCurrent',
}

registerComponent('App', App, withCurrentUser, [withEdit, editOptions]);

export default App;