That largely depends on four very important questions:

1. How much of it do they convert to another form of currency in a single year?
2. What jurisdiction do they live in?
3. What other income do they have in that year?
4. What deductions and credits are available to them that year?

Well, depending on which state they live in, there may also be some state income taxes. I can't think of any counties or cities with a capital gains tax, but I suppose it's possible.

It's also possible that they'll be subject to the Net Investment Income Tax (established in 2010 as part of the Health Care and Education Reconciliation Act). If so, then some portion of that income would be subject to an additional 3.8%

Additionally, depending on what other sources of revenue they had that year, it's possible that the AMT would increase the amount of their capital gains that would be subjected to the 20% rate instead of the 15%.

There are opportunities to reduce this tax burden though depending on many things such as what they want to do with this money and what time of year they are wanting to make the sale. It would be a good idea for such a person to work closely with a tax attorney and/or qualified financial planner familiar with their jurisdiction.

Don't know. Don't care. I don't live in El Salvador.

Perhaps use your telephone to call up a financial advisor in El Salvador and ask them?