Wie nannte das umgekreiste Ding in Deutsch?

And also how much would it cost to get it replaced in Munich?

That’s an „Eckventil“. You can get them at the hardware store (Baumarkt), or call a plumber (Klempner) to have them replace it.

Are you looking and changing the whole thing or just the wire mesh hose? Both you can change yourself and buy at hardware store. ( Providing you have the tools ) . It’s easy until you get to the actual Mixer above.

(Likely) cold water eckventil. Cold is normally rightside while Warm is on the left. In old buildings you can’t always be sure they did it correctly though

Rosette.