code: protected static String getLang() {
          Locale locale = Locale.getDefault();
  
          if (null == locale)
              return DEFAULT_LANGUAGE_CODE;
  
          String language = locale.getLanguage();
          String country = locale.getCountry();
          String localeString = String.format("%s_%s",
                  language != null ? language.toLowerCase(Locale.ENGLISH) : "",
                  country != null ? country.toUpperCase(Locale.ENGLISH) : "");
  
          // 1. if no language is specified, return the default language
          if (null == language)
              return DEFAULT_LANGUAGE_CODE;
  
          // 2. try to match the language or the entire locale string among the
          // list of available language codes
          String matchedLanguageCode = null;
          for (String languageCode : VALID_LANGUAGE_CODES) {
              if (languageCode.equals(localeString)) {
                  // return here as this is the most precise match we can get
                  return localeString;
              }
  
              if (languageCode.equals(language)) {
                  // set the matched language code, and continue iterating as we
                  // may match the localeString in a later iteration.
                  matchedLanguageCode = language;
              }
          }
  
          if (null != matchedLanguageCode)
              return matchedLanguageCode;
  
          return DEFAULT_LANGUAGE_CODE;
      }
docs: Gets the current language, guessed from the system.
  
  @return The locale in use.