Automatically selecting a language based on the Accept-Language header value can be a nice feature but isn't a universal solution, and there are reasons to not

Automatically selecting a language based on the Accept-Language header value can be a nice feature but isn't a universal solution, and there are reasons to not do it. As another commented noted, it can be helpful to have the desired language specified via the URL for bookmarking and permalink reasons. Another problem is that some users don't know how to configure their browsers to declare a preferred language. Another problem is that some users do not have a single preferred language, and may prefer one language for certain contexts and another language for others. For such users, it's preferable to simply pick the language that they want from the site's UI. Some sites automatically choose a language based on the client's location, and for similar reasons, this can be more annoying than helpful to certain users.