Hi, I consider to do an LLM at Ruprecht Karls University in Heidelberg, mainly as they offer a dual program. One year in Germany and another one in the states at Hastings College in California. Has anyone experience with this? How difficult is it to get a Visa?

Interesting: I've not heard of this dual program before, and am not able to find a reference to it on the Ruprecht Karls website, would you mind linking to it?

In general, study visas are not that hard to get in the US. You'll probably need an F1 visa - which requires you to have a foreign residence, and to be able to demonstrate financial support and strong ties to your home country (they don't want people who are just using the visa to move to the US).

Usually, the law school will help you with the process. This is generally not something to worry about.