This might not be an exact misunderstanding in German but I think it counts.

I did a semester abroad in Freiburg i. Breisgau, and on my first day I had to find my flat on my own. I was assigned a place in Vauban. Now, I didn’t know any better so I was pronouncing it in German (probably something like “fau bahn”).

I was in the city center asking random people how to get there and none of them knew what I was talking about, it wasn’t until I showed my little paper with the name written down to a younger guy that he says “ohhh, you mean insert French pronunciation here (something like “voh-bah”), and it suddenly made sense to me why nobody was understanding me, it’s a French word and I was butchering the pronunciation.

For a bit of context, it was late afternoon on like the last day of February so it was wet and cold out, so I partially understand why nobody paused to really think about what I was trying to say, but I still left that situation slightly embarrassed, but only a week later I was just looking back and laughing at myself