code: public String getLanguageKey(String path) {
  
          // Parse language key from filename
          Matcher languageKeyMatcher = LANGUAGE_KEY_PATTERN.matcher(path);
          if (!languageKeyMatcher.matches())
              return null;
  
          // Return parsed key
          return languageKeyMatcher.group(1);
  
      }
docs: Derives a language key from the filename within the given path, if
  possible. If the filename is not a valid language key, null is returned.
  
  @param path
  The path containing the filename to derive the language key from.
  
  @return
  The derived language key, or null if the filename is not a valid
  language key.