International travel more than doubled from 2000 to 2020, thanks to rising discretionary income and cheaper foreign flights, as more low-cost carriers entered the market.

从2000年到2020年，国际旅行增加了一倍多，这得益于可自由支配收入的增加，以及越来越多的低成本航空公司进入市场，国外航班更加便宜。

Yet in developed countries a large proportion of people have a nontrivial amount of discretionary income to play with.

然而，在发达国家，很大一部分人拥有大量可自由支配的收入。