Ads and landing pages change with the country. To see what a user in the United States sees, the address has to come out of the United States. There is no shortcut through a language setting.
The care
Use one address per market and do not mix markets in the same browser profile. A cookie from one country inside a session from another contaminates the measurement.
Check the country in the IP location tool before recording the result. The city does not matter here; the country does.