The GP poster is incorrect; the Region setting has nothing to do with setting the region code of the Language setting (each language+region pair being its own listing in Languages.) The Region you choose during initial device setup does determine your
default Language region, but you can pick a different one while keeping the same Region.
The Region setting in iOS is literally just the question "what Country [or Country-equivalent political region] would you like to be considered to be in, when we make certain OS features be dependent on your country?"
This is separate from what country the phone treats you like you're actually in, geographically, which is determined moment-to-moment by geolocation and cellular profiles. (Time zone? Geolocation. Maps domestic/foreign feature display granularity? Geolocation.)
Whereas, Region is for things like, say, whether you see certain apps or features that are in partial progressive rollout; or whether you see features offered that don't make sense outside of certain regions.
Re: the first example, the News app, which rolled out in the US first, could be made to appear in other countries by setting your Region to the US. When this was done, the News app, if launched, would still detect what country you were actually in (geolocation-wise), and would make a best-effort attempt at showing news from the few sources Apple had made agreements with so far from that country.
Re: the second example, iOS has social-network "Accounts" integration with Sina Weibo, QQ, etc. just like it has integration with Facebook/Twitter/etc. It just doesn't display these sign-in options unless your phone is set to the China "Region." Because, if you're not in China or from China, why would you ever use these networks? (Note that Apple designs iOS under the assumption that people won't bother to change their Region when they travel; so it really is more of a "where are you from" rather than "where are you now" question.)