After they were done, I approached them to ask what was one piece I hadn't recognized. Assuming they were italian, I said - Bravi!- and proceeded to my question. And they asked me if I could speak english.
We talked a bit in english (the misterious pièce was one of Brahms' dances) and we said goodbye to each other. But they weren't from an english-speaking country, they were speaking to each other in some eastern european language, I am not able to recognize which one.
Some thoughts sprung to my mind:
Firstly, they found a genious way to self-sustain during their vacation (they got lots of money from people who were listening)
Second, it is really wonderful to be able to communicate in the same language, even though we come from very different countries. Italian and their language have nothing in common. But we understood what we were talking about because we both could speak english. This is not a given as it could seem. It is just great!
Finally, music is really an universal language. People who stopped to listen to them were from everywhere, and they all appreciated what they were playing. Brahms is Brahms, and is beautiful, whether you are from Brasil or from France. I am not talking only about classical music: any kind of music is "unifying" in my opinion: it trapasses the difference in language and nation. And this, again, is great.