code: public List<String> getRuleFileNames() {
      List<String> ruleFiles = new ArrayList<>();
      ResourceDataBroker dataBroker = JLanguageTool.getDataBroker();
      ruleFiles.add(dataBroker.getRulesDir()
              + "/" + getShortCode() + "/" + JLanguageTool.PATTERN_FILE);
      if (getShortCodeWithCountryAndVariant().length() > 2) {
        String fileName = getShortCode() + "/"
                + getShortCodeWithCountryAndVariant()
                + "/" + JLanguageTool.PATTERN_FILE;
        if (dataBroker.ruleFileExists(fileName)) {
          ruleFiles.add(dataBroker.getRulesDir() + "/" + fileName);
        }
      }
      return ruleFiles;
    }
docs: Get the location of the rule file(s) in a form like {@code /org/languagetool/rules/de/grammar.xml},
  i.e. a path in the classpath. The files must exist or an exception will be thrown, unless the filename
  contains the string {@code -test-}.