Excuse me, ...?

Hello everyone,

I wanted to ask you what to do (/what you do) when you hear someone talking
in an interesting sounding language you do not know but it would be unpolite
to ask in that situation (e.g. someone is speaking to his/her
telephone/mobile, the table next to your one in a restaurant, ...).
I had this situation recently, I'm still wondering whether I should have
asked or not.

Carsten