If cookies are only used for preferences functions, then I should expect that it should only require to mention the cookies in the preferences menu (I hope)? If they have a document to explain each cookie by name, then it would also be helpful, that you can enable/disable them individiaully (or make them read-only) by the browser settings. However, for some things such as languages there are other ways to do without using cookies, such as Accept-Language header for languages, although cookies could be used to override the Accept-Language header in case both are present in the request.