public Optional<EmailNotificationTemplate> findTemplateFor(String reasonKey, String localeTag) {
        Locale bestMatchingLocale = Locale.lookup(Locale.LanguageRange.parse(localeTag), supportedLocales);
        return findTemplateFor(reasonKey, bestMatchingLocale);
    }
Send an HTML email with a plaintext fallback/alternative.
manager/api/rest-impl/src/main/java/io/apiman/manager/api/notifications/email/SimpleMailNotificationService.java