Article queries now respect the reader's locale

The article listing, search, by-category, and by-tag endpoints used to serve content in the default locale only, ignoring whichever language the reader was browsing in.

Every one of those endpoints now accepts a locale parameter and returns the appropriate translation when one exists, falling back gracefully to the canonical content when it doesn't.

From the reader's perspective, this means category and search pages now show Spanish titles to Spanish readers, English titles to English readers — instead of the awkward mixed-language lists you might have seen before.