I am running the site with a Danish interface. I\m guessing if you make no changes at all to the default text, the Discourse platform has the translation already done, but as soon as you customize it, it defaults to the English you enter.
Maybe make a very minor change to customize the text in the General Discussion so it stays in English. That way you wont get messages asking why only part of the site is translated. See scereen capture for details.