I have a financial spreadsheet in which I have built macros for local data
versions .. when you click on a flag of the country, it goes through the
spreadsheet, updates some base data, changes to local currency format.

So, when I click on the German flag, it changes the contents and the
currency format ( to Euros). When I click on the US flag it switches the
content back and changes to US $.

A user downloaded the file in the UK. When he clicked on the German flag it
did exactly as described above, but when he clicked on the US flag, the
currency instead of changing back to US $ changed to UK pounds?

Any idea what is happening?

Thanks in advance for any suggestions on how to fix.