Thanks for the reply.
Meanwhile I found a workaround.
I realized that the posts were still visible by calling their url directly. So I got the IDs of all the posts from the database and merged them into strings like “https://www.mysite.com/wp-admin/post.php?post=4494&action=edit”. By visiting the edit url and saving them one by one, the posts have been re-assigned to their original language.
