Preferences like that should be part of the URL schema. Picking language as a good example, a site can use a path variable (eg the part of the page URL after the domain) to store that information. https://example.com/en/page.html, https://example.com/de/page.html, https://example.com/es/page.html, etc. Alternatively a site could use a subdomain for the same thing. There are many advantages to that approach, such as making it easier to route traffic to a local data center or leverage better edge caching for localized assets. It also means users can deep link straight to a page in their chosen language.