If you want to take a photograph of someone, ask first. If they don’t speak the same language as you, make eye contact, show them your camera, and wait for their response. If they nod their head, “yes” take a photo or two. If you think it’s appropriate, you can show them the picture too.
Don’t forget to e-mail a copy to yourself too. You never know when you might need to have some sort of documentation with you and might not want to carry your original.