docs: public static String createResourceFilesRegex(String fileName, String fileExtension) {
  		if (fileName == null) {
  			throw new IllegalArgumentException("Parameter fileName must not be null.");
  		}
  		if (fileExtension == null) {
  			throw new IllegalArgumentException("Parameter fileExtension must not be null.");
  		}
  
  		StringBuilder strBuilder = new StringBuilder(fileName.length() + LANGUAGE_LOCALE_REGEX.length()
  				+ COUNTRY_LOCALE_REGEX.length() + fileExtension.length() + 13);
  		strBuilder.append(Pattern.quote(fileName));
  		strBuilder.append("(?:_").append(LANGUAGE_LOCALE_REGEX);
  		strBuilder.append("(?:_").append(COUNTRY_LOCALE_REGEX).append(")?").append(")?");
  		strBuilder.append(Pattern.quote(fileExtension));
  		strBuilder.append('$');
  		return strBuilder.toString();
  	}