Looks like the endpoint only applies the Accept-Language for the first time.
Change 554150 had a related patch set uploaded (by Mholloway; owner: Michael Holloway):
[mediawiki/services/mobileapps@master] Fix: Apply language headers to mobileview (zhwiki) mobile-html response
Change 554150 merged by jenkins-bot:
[mediawiki/services/mobileapps@master] Fix: Apply language headers to mobileview (zhwiki) mobile-html response
Mentioned in SAL (#wikimedia-operations) [2019-12-03T03:47:38Z] <mholloway-shell@deploy1001> Started deploy [mobileapps/deploy@d00c6ad]: Fix: Apply language headers to zhwiki mobile-html responses (T239659)
Mentioned in SAL (#wikimedia-operations) [2019-12-03T03:53:30Z] <mholloway-shell@deploy1001> Finished deploy [mobileapps/deploy@d00c6ad]: Fix: Apply language headers to zhwiki mobile-html responses (T239659) (duration: 05m 51s)
Hi @Mholloway
Just found this article still has the issue:
https://zh.wikipedia.org/api/rest_v1/page/mobile-html/物联网
Not sure if the redirected title affects the Accept-Language setup?
I tested just now, and the Accept-Language header is honored when I request that page. I see that the page was edited this morning, so it's possible that an old version without the header adjustments was coming from RESTBase or ATS/Varnish but has now been replaced.