Modifying url to fix error 404

Hi,
I have installed the plugin in its version 1.1.18 and I have translated my site in two languages; Spanish and Catalan.
The url that it is genered is, for example, http://www.mydomain.com/es/contacto or http://www.mydomain.com/ca/contacte but if someone write http://www.mydomain.com/contacto or http://www.mydomain.com/contacte, the url that is returned is broken with 404.

¿can anybody help me?

Thank you very much,
Sara