I’m sorry, but your suggestion didn’t help me.
I downloaded the whole wordpress folder and searched in every *.php, *.html, *.xml, *.css and *.js file.
I’ve not found the link or anything about the link (I searched for “Schweiz”).
Is there another way to find the source where this link comes from?
It is so strange. It is only me who has access to this page.
I don’t know why it happened.
Thanks for any further steps I could try.