When you use the search controller in a lane that doesn't have any language restrictions, your search is limited to the languages sent in your browser's "Accept-Language" header. This makes sense for patrons, but it's not good for librarians, who may want to search without the language filter.

We can add a 'language' argument to the search controller which overrides the "Accept-Language" header (even if only to zero it out), just like that controller has a "medium" argument which overrides any value set by the entrypoint.