code: @RunAsSystem
    public Map<String, String> getMessages(String namespace, Locale locale) {
      return getL10nStrings(namespace)
          .stream()
          .filter(e -> e.getString(locale) != null)
          .collect(toMap(L10nString::getMessageID, e -> e.getString(locale)));
    }
docs: Gets all messages for a certain namespace and languageCode. Returns exactly those messages that
  are explicitly specified for this namespace and languageCode. Does not fall back to the default
  language.
  
  @param namespace the namespace for the messages
  @param locale the Locale for the messages
  @return Map mapping messageID to message