Currently, we gather languages from Accept-Language to get an idea of which languages the user might be interested in reading.

But we only use this information if the lane they're searching has no language filter of its own. If the lane has a language filter (and all of them do, generally speaking), Accept-Language is ignored.

We used to use Accept-Language instead of the lane's language filter, and we got a lot of complaints from patrons who read in English rather than the language of their mobile device. But now we get complaints from patrons who do read in the language of their mobile device and can't find or search for books in their language.

Searching in the union of the the lane languages and the device languages seems to give good results. A search request is in one particular language, and although we don't know what language that is, we can usually narrow it down to one or two likely options.

The main problem is going to be for books that were translated between languages but kept the title. Both languages will show up side-by-side, but SimplyE doesn't make it obvious which language a book is in. So there's a chance you'll check out a book in the wrong language.  (This is what patrons complained about back before we instituted the language filter in the first place.) However, with this change in place it's less likely to be a language that you can't read at all – it'll either be the language of the lane you searched or the language of your device.