Not the OP, but I think you bring up a great point and just wanted to chime in...
IMO cultural compatibility is valuable and worth paying a premium for, both within an employer's team, between an employer and their customers or their marketers, etc.
The support culture can be vastly different between cultures, as can design sense, time prioritization, team dynamics, etc. It's hard to work effectively with someone who barely speaks your language, doesn't get your jokes, doesn't like the same food, isn't used to communicating the same way -- whether in body language or slang or powerpoints, etc. (And it goes both ways -- I'm not just talking about American companies offshoring, but also Americans trying to work overseas, or people moving to/from China for opportunities, etc.)
But in an actually free market, where capital, labor, and customers are all free to pick and choose as they please, I doubt the difference would be as large as it is now, like 5x-10x difference for the same work just based on cultural compatibility. I've met plenty of foreign (to me) people who work harder and are just plain better at my job than I am, but get paid less because of the circumstances of their birth.
In a hypothetical world where people were free to work and live where they please, I don't know what an appropriate value of that "cultural fit premium" should be, maybe 20-30%? Certainly not orders of magnitude. But we don't have that hypothetical world, and our protectionist borders seem to be getting more defined by the day, not more blurred, as the West goes through a cultural backlash against globalization.
The dark side of "equal pay for equal work" is that Americans often enjoy higher pay and a higher quality of life for less work, sometimes MUCH less work, compared to their counterparts in international tech sweat-shops. We have hard-won labor protections that took decades of organizing to achieve, and even then there are horror stories of abuse and burnout.
Ideally we'd be paying all workers the highest wages and letting them move where they please, but doing so would also cause hyperinflation across the world and in turn drive down purchasing power. And cause a horrifying housing crunch in all the desirable areas of the world. The whole system is rigged such that there can ever only be a small % of comfortable people, or else it all falls apart =/
Other options are to pay the lowest common denominator (and lose all your highest paid staff), just don't outsource, or apply a cost of living adjustment, etc. None are perfect or easy solutions.
But salary transparency is a great start, especially while there are still people doing the same job in the same OFFICE, sometimes on the same team, who get paid differently. It at least gets the conversation going so we can start thinking about solutions...