Introduce LLAppViewer::initStrings(); reload default_trans_args. Calling LLTrans::setDefaultArg() after LLTransUtil::parseStrings() is almost good enough -- but it fails to address the case in which one or more of the default_trans_args strings (e.g. "create_account_url") embeds a reference to the new substitution. So after the setDefaultArg() call, go back through default_trans_args, refetching each string to perform the substitution and updating it with a setDefaultArg() call of its own. All this is way too much logic to replicate in both LLAppViewer::initConfiguration() and init(), so break out new LLAppViewer::initStrings() method and call it from both places.