Resolve "Update yarn."

Closes #55 (closed)

Generally it looks fine to me, but the language switch behaves weirdly. The language tag does not show up in the URL and the link to the Enlish version stays gray regardless of whether I have switched to English or German. Is this caused by the yarn update? @gabriel.preuss @jan.schweikert

Edit: The language switch issues have been either resolved or moved elsewhere. We now just need to make sure that the newer yarn works for everyone as intended.