You are right, but for xkcd it's a concept to have a second joke in the alt text since forever. There used to be a transcript of all comics right on the site available for those that need it, but it has been discontinued, probably in favor of explainxkcd.com, where you'll still find a transcript for every comic.
Not wanting to use the browser is its own purpose? Of course I understand if you want to use a specialized app that offers more features, better usability, nicer layouts than the original websites of the services they are for. But using a specialized app just because it's not the browser (which, by the way, it often really is anyway), why that?
As this is a labelling issue, you can directly make a proposal in the translation tool. In this case, it was already changed before this post was made, see my other comment with link.
