Javelwasser is just the same as Clorox, a straight bleach that will not remove mineral deposits (kalk) at all. Go to Coop and get WC-Ente, WC-Gel forte. Squirt it around the inside of the rim, let it spread down then smear it around with the toilet brush. Let it sit for 10-15 minutes, then brush around the rim and down in the siphon again and flush and you're done, if not, repeat. Should now be sparkling clean and fresh.

Do not scrub or scrape with anything abrasive. That will just scratch the porcelain and make a surface that mineral deposits adhere too even bettter.