This should be done in the report template.
You can access the invoice template from the GUI. You need to open the
Administration -> User Interface -> Actions -> Reports main menu item.
If you then find the
Invoice report and switch to form view you can use the
Save As button (downward pointing arrow) in the
Content field to download/open the Invoice Template.
Once you have made the changes that you want, you then clear the
Content field using the button with a
X and use the magnifying glass button to select the invoice template you want to use.
I don’t think this is possible, but you could add different sections to the report and use
if statements to only render the parts that are applicable to the various countries.
Also translations can be enabled on reports to translate them dynamically into different languages.