If you support multiple currencies on your site, then use a drop down to enable shoppers to select the currency and/or the country. Ensure the option to choose the currency/country is highly prominent. If you can automatically detect the geographic location of the shopper, then set the default currency/country based on the location.
Since automatic country selection is not always accurate, you can also ask the users to choose the country when they first enter the site and allow them to change it any time.
If your store is localized in 2 or 3 languages, then list them using the language’s own name itself across the website header so that the user can toggle between them.
If yours is a multilingual store, then use a drop down language selector that lists all the languages in alphabetical order.