Feign no English.

The man's face lights up with relief. Babbling something in what, you suspect, is the same language-you-don't-understand that the opera was in, he hands you the painting then staggers off into the gloom.

You can:

Chase after him. He has a bad leg, he can't have got far.

Try to find some light so you can take a look at the painting.

Place the painting on the ground and abandon it.

Shout, "Hey! What's wrong with using English?" after the man.

You notice the sound of people running nearby. They are probably coming in your direction.