Are foreign retirements taxable in the US?

Usually the country that you are a resident of gets to tax your foreign retirement income.

As a US Citizen or Resident alien you are required to report all of your gross worldwide income on your 1040 income tax return.

But you do have some tax treaties with some country that can be complex so you should check this out to be sure you handle it correctly on your federal 1040 income tax return to make sure that it is completed correctly.

Go to the IRS gov web site and use the search box for The Taxation of Foreign Pension and Annuity Distributions or Publication 519 U.S. Tax Guide for Aliens

Resident Alien.

A resident alien's income is generally subject to tax in the same manner as a U.S. citizen. If you are a resident alien, you must report all interest, dividends, wages, or other compensation for services, income from rental property or royalties, and other types of income on your U.S. tax return. You must report these amounts whether from sources within or outside the United States.