> error_msg would be easy to pick up for translation, rather than have to do some cludgy import as _ and _("Internal error!"). Hm, now that I'm writing this here, I guess it's still not a type you'd want to operate differently on than just plain unicode strings.

This is maybe ok for very simple cases, but doesn't work as soon as you need context (in Python this is either done by extra _ parameters or through special comments) or pluralization.