It's so standard in web frameworks and CMSes that you must see it in action every single day without realizing it, as long as the sites are using the built-in i

It's so standard in web frameworks and CMSes that you must see it in action every single day without realizing it, as long as the sites are using the built-in i18n capabilities - which in almost all cases they are. And in Apache/Nginx configs that involve header-based redirections to a local language domain/subdomain, same deal.