That is because you changed the original chinese title into “Global Cloudflare Outage”, not the english translation of it. Using the pencil in the post menu makes it easier to see the distinction.
You also completely the title language, which would need to reset the whole language detection into translation flow over again.
I guess the bug here is that the quick edit for title / category / tags doesn’t support the popup for picking which locale needs to be translated. As this can get quite tricky, I propose that we disable the whole quick edit when viewing localized topics. When clicking on the pencil for quick edit, it should popup the locale picker modal and open the composer for the OP.
Ok, so now I used Google translate to translate “Global Cloudflare Outage” back into Chinese.
Then I used the post-pencil and edited the Chinese topic title.
Then I had to use the post-pencil and edit the English topic title, which got me where I wanted to be.
However, when I switch to German, it still says “Als ich aufwachte, explodierten sie alle”. And I assume that goes for every other language as well.
So I guess that in addition to your proposed workaround, an edit of the original title should also trigger a re-translation of the title into the other languages.