After installation of i18n I setup my "article" content-type to be translatable. I have activated the "URL" language negotiation. After translating node/17, I get a new node/18. I activate the language switcher, which links from node/17 to da/node/18. Unfortunately, with the language prefix, this returns a 404.
Manually removing the path prefix from the URL shows the node as expected.
This seems like a bug, but maybe some configuration that I don't understand/find is necessary?