Feature articles have been in the service for a while and are a great addition to the app feed. We should add support for languages beyond English.
This task is to add the languages which support the FeaturedFeed ext. convention of TFA (minus zhwiki since we don't support language variants in RB yet).
Example URI: https://en.wikipedia.org/wiki/Special:FeedItem/featured/20170306000000/en?useskin=apioutput.
See T148680#3078906 for more details of the approach.