You literally have cities in China that are called "second wife villages"(二奶村) where politicians and rich people have their mistresses that are located close to ports/airports for quick access on "work trips". In Shenzhen for example its the Luohu (罗湖) and Futian (福田) districts that are for this purpose.

It’s much more than Japan: Chinese in other countries, Philippines, etc. I’ve met in person sons and daughters from “second families”.

Also the French, so it’s not exclusively a practice of East Asian people.

Don't make it sound like Japan either. It's just not possible where no family with a connection to someone powerful would be satisfied hidden away in a rural village. When caught by a tabloid, your career ends completely, not really excepted behavior.

Confident much or are you playing on concubine vs wife game word?