Germany does not have a separation of state and church. That's not something that exists in the constitution. We have a right to freedom of religion (with a bunch of caveats) and we don't have a national religion. But that's pretty much it.
Heck, the Federal Republic of Germany upon its foundation decided to uphold its end on contracts with the Catholic church dating back to the German Empire and even before that by arguing itself to be the "legal successor" of those entities. This results in a bunch of oddities like Germany literally paying money to parts of the Catholic church (for leases, debts and such), churches (and formally church-run organizations even if they're 100% state-funded) being exempt from most labor laws and yes, the tithe being collected by the German tax agency.
However formally this is not specifically tied to Christianity. It's just defined in such a way making it extremely difficult for any other religious group to qualify in the same way after the fact.
Heck, the Federal Republic of Germany upon its foundation decided to uphold its end on contracts with the Catholic church dating back to the German Empire and even before that by arguing itself to be the "legal successor" of those entities. This results in a bunch of oddities like Germany literally paying money to parts of the Catholic church (for leases, debts and such), churches (and formally church-run organizations even if they're 100% state-funded) being exempt from most labor laws and yes, the tithe being collected by the German tax agency.
However formally this is not specifically tied to Christianity. It's just defined in such a way making it extremely difficult for any other religious group to qualify in the same way after the fact.