Shopify locale aware URLs
If you are using the Shopify Markets functionality to make your store available to multiple currencies or languages. You are likely using locale aware URLs, which add something like this to your URLs:-
yourdomain.com/ <- Without locale
yourdomain.com/en-gb/ <- With locale
When using these you need to ensure that you avoid hardcoded URLs within your theme, to avoid accidentally bouncing a customer to the wrong locale, where they might get the wrong language or currency.