My first pass would be:
– Is there an article in the user’s transmitted native language? If yes, return in order of their preference, and stop.
– Is there an article in the language of the country the request is transmitted from? If yes, add to the head of the list of options and continue processing.
– Is there an article at all? Add to the tail of the list of results.
– Return the list of results.
There’s basically only a limited number of things you can do here, and when you know you don’t know, you need to be as helpful as possible. I think it’s not unreasonable to assume that since someone is in a country they probably have a grasp of the language – it may not be enough to understand everything though, so to me it seems to a “we think you’ll probably want this, but we don’t know” is probably the way forwards. Essentially, it’s showing the search results in the order in which you’re expecting the user to probably go for them.
Most helpful with least impact when you’re wrong is probably the mantra here.