# Letting the user pick a language: ?lang=mr with a cookie resolver, and two ways to get it wrong


--- A. CookieLocaleResolver named localeResolver + LocaleChangeInterceptor (profile 'cookie') ---
no cookie yet, Accept-Language: hi        -> status=200  locale=en  message=Hello, Asha!
?lang=mr, Accept-Language: hi             -> status=200  locale=mr  message=नमस्कार, Asha!
Set-Cookie: lang=mr; Path=/; Max-Age=2592000; SameSite=Lax
Cookie: lang=mr, Accept-Language: hi      -> status=200  locale=mr  message=नमस्कार, Asha!

--- B. the same resolver under the bean name cookieLocaleResolver (profile 'cookiewrongname') ---
Accept-Language: hi                       -> status=200  locale=hi  message=नमस्ते, Asha!
?lang=mr                                  -> status=500 (Tomcat's own HTML error page)
bean 'cookieLocaleResolver' exists: true
bean 'localeResolver' is a: AcceptHeaderLocaleResolver
what the interceptor triggers: UnsupportedOperationException: Cannot change HTTP Accept-Language header - use a different locale resolution strategy

--- C. only the interceptor, Spring Boot's default resolver (profile 'interceptoronly') ---
?lang=mr                                  -> status=500 (Tomcat's own HTML error page)
bean 'localeResolver' is a: AcceptHeaderLocaleResolver
what the interceptor triggers: UnsupportedOperationException: Cannot change HTTP Accept-Language header - use a different locale resolution strategy