Changed CultureMiddleware to check if the culture cookie value is in the list of supported languages, not just for null or empty. This ensures that only valid, supported culture values are accepted from the cookie; otherwise, the middleware falls back to Accept-Language or default logic.
When no culture cookie is present, use the browser's Accept-Language
header to determine the user's preferred culture. This culture is
applied and stored in a cookie, enhancing localization by respecting
user preferences instead of always defaulting to the application's
default language.
