setLocale (locale) {
    if (has(this.options.locales, locale)) {
      this.options.locale = locale
      this.selectedLocale = locale
      // Trigger validation on all forms to swap languages
      this.registry.forEach((form, name) => {
        form.hasValidationErrors()
      })
    }
  }
Change the locale to a pre-registered one.
@param {string} localeTag