People joke about that, but it does well for me in English, French, and Spanish. I run into functionality limitations with Siri, but it's not usually a matter of not understanding my words.I would settle for Siri understanding me when I speak only English.
Do you listen to any non-English music? Or think that non-native English speakers listen to any English-language music? It's hit or miss—usually miss—whether English Siri will be able to find and play a song with a non-English title from my Music library. I've set up Playlists with English names that have sets of music so that I can ask Siri to play them when I'm in the mood.