Subscribe To Comments Reloaded does exactly what it says it does. It provides a couple of easy-to-configure options to taylor comment subscriptions and user messages to your needs. Bonus: you can set up your own page template for subscription management.
I hope the plugin author will continue to maintain the plugin and keep it up to date with WordPress. If needed, I'd totally be willing to beta test new versions and update the German translation files. Please feel free to get in touch, camu!