How to use the fbt.IntlViewerContext.locale function in fbt

it('should raise an error when mutate locale property not string', () => {
    // $ExpectError: need string
    IntlViewerContext.locale = 123;
  });

setLocale(locale: Locale) {
    IntlViewerContext.locale = locale;
    this.setState({locale});
    const html = document.getElementsByTagName('html')[0];
    if (html != null) {
      html.lang = LOCALES[locale].bcp47;
    }
    document.body.className = LOCALES[locale].rtl ? 'rtl' : 'ltr';
  }

setLocale(locale: Locale) {
    IntlViewerContext.locale = locale;
    this.setState({locale});
    const html = document.getElementsByTagName('html')[0];
    if (html != null) {
      html.lang = LOCALES[locale].bcp47;
    }
    document.body.className = LOCALES[locale].rtl ? 'rtl' : 'ltr';
  }