code: public Locale getMainTranslationLocale(Locale defaultValue) {
  
          Map<String, String> params = getParameters();
          String value = params.get(PARAM_MAIN_LOCALE);
          if (!CmsStringUtil.isEmpty(value)) {
              return CmsLocaleManager.getLocale(value);
          } else {
              return defaultValue;
          }
      }
docs: Gets the main translation locale for this site.<p>
  
  @param defaultValue the value to return as a default when no main translation locale is set
  @return the main translation locale