Language settings - UK, US etc.?

How do they affect ad display?

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How do the language settings affect where our ads will show? If we select "English - United Kingdom" will it only show for people who have set their computer to United Kingdom English?

The help says:
"For example, choosing English - United Kingdom will allow your ads to be shown on all MSN websites ending with co.uk."

What if we wish our ad to show who people who have both English - UK and US?

Thank you very much :)