In addition to the requests to Parsoid passing the Accept-Language header (T195948), MCS should also request the correct language variant for the values we get from MW API. A few areas that come to mind are:
- summary: description, titles
- metadata: categories, hatnotes, issues, toc,
- media: titles, descriptions, captions, artists, license strings, ...
- mobile-sections: for the main page content we still use action=mobileview