Musician, Khiva, Uzbekistan. Photographing people who are performing for you solves the basic problem of permission when travelling.
Fujifilm X-H2, 8-16mm, f3.6 @ 1/25 second, ISO 3200
Perhaps the best aspect of travel with a camera is photographing the people you see and meet. Different faces, different clothing, different customs – there is a wealth of material for us to capture.
When it comes to photographing people, there are many traditions we can follow. We all know about Henri Cartier-Bresson and how he photographed as a silent observer. Richard Avedon used a more formal approach, inviting his subjects to pose on an improvised set. There's no right or wrong, as long as we are respectful.
My suggestion is to consider how you would feel if you were at home, going for a run or to pick up a coffee, and you saw a tourist sneaking a few photos of you with their phone (or camera). Or you caught someone across the road with a telephoto lens photographing you as you put out the rubbish. Even if the tourist walked up and started talking to you, how would you feel if they then asked if they could take your photograph? Yet this is exactly what most travel photographers do on a regular basis and all I can do is thank the world's population for being so (generally) very accommodating!
So, what should we do? I think the answer is to play it by ear. There will be occasions when life is busy and you can take candid photographs without being noticed. We all have our special techniques for pretending not to be taking a photograph, or shooting from the hip as we walk by. Then there will be other situations where our presence is quite obvious and our subjects not so tolerant – are we better off putting our cameras away and just enjoying the experience.
We can also smile and ask permission to take a photograph. The answer can depend on how you build up to your request. How would you react if someone walked up to you in the street and asked to take your photograph? Compare this with someone asking you for directions, having a conversation and then asking you? And the fact you can't speak their language can often be a benefit as facial expressions and gestures can communicate all that is needed.
We don't have to photograph every person we meet. We don't have to photograph every great character we see, just because we think they would make a great photograph. There will always be other great portraits around the corner.