if you not using cms.middleware.multilingual.MultilingualURLMiddleware, your template's show_menu will report a error such as "Caught AttributeError while rendering: 'WSGIRequest' object has no attribute 'LANGUAGE_CODE'" and the traceback's answer is at menu_pool.py line 43:

so shoud the source be like this in menu_pool?

def _build_nodes(self, request, site_id):
lang = getattr(request, 'LANGUAGE_CODE', 'settings.LANGUAGES_CODE')