Why the German police?

Question

In Captain America: Civil War, the Winter Soldier (Steve Rogers's childhood friend Bucky Barnes) is sought for his role in an assassination and located in Bucharest, Romania. We know it is Bucharest because they tell us he is in Bucharest, print the word "Bucharest" on the screen in big letters, and subsequently refer to "back in Romania."

The police that come to bust him are German special forces. We know this because they have German on their uniforms, they speak German, and they are referred to specifically as German special forces by our protagonists.

My question: why are Germans arresting people in Romania?

Answer 1

The movie doesn't make any attempt to explain it, but the decision to send in the German special police is a combination of simplifying things for the audience, plus attempting to paint the Sokovia Accords as a true international agreement.

The crime that Bucky was wanted for happened at a United Nations meeting in Vienna, Austria, but Barnes himself was located in Romania. The actual politics involved in can be tricky, involving the EU police cooperation agreements and the Europol agency, which I suspect is something unfamiliar to a lot of people. Explaining that process would be a waste of screen time.

More importantly, the whole idea of the Accords is that the countries in the UN are coming together to shore up global security, with the locking down of the Avengers being the biggest part of that. The idea here appears to be that the German special forces were acting on behalf of The UN, with full cooperation from Romania. It's likely that, being in Austria, Germany's special forces may have been recruited to act as police for the UN meeting itself, and were thus sent after Bucky because they were already mobilized and ready to go.