It is hard to visit /acs-lang/admin/load-catalog-files when I can not login.
I already tried what Robert mentioned above (loading /foo.tcl with lang::catalog::import -locales [list "en_US"] in it).
Just to make sure I removed the "-locales [list "en_US"]" part so it more closely resembles /acs-lang/admin/load-catalog-files and tried it again. No luck, same error on registration.