One of them was a little pissy with me because I didn't respond when she was calling out 'ma'am' from several metres away. I continued to have a polite, low toned conversation with her in German while she kept asking me things in English and told her that since she was in Germany, at a German airport, speaking to German passengers she could ask me the questions in German and I would be happy to answer her questions in German.

If I showed up at an airport in the US and was asked questions in Mandarin, I would politely suggest that they ask me questions in English.