Naomi Wu has been talking about this for a while [0]. She lives in China, and has flagged this multiple times on Twitter, apparently without much response from the Signal team to her frustration. The issue seems to be that Signal simply sets the incognito flag when users are typing in the app, which kindly requests keyboard apps to not track the input. Unfortunately, since most American made keyboards for chinese writing are slow and difficult to use, most Chinese citizens use keyboards made by companies made in China, which does not provide much reassurance w.r.t adherence to the incognito request. Your concern seems to be spot on, and it'd be worth Signal at least making this clear to users when they first begin using the app.
While the answer from most technical users will be "just switch keyboards", it's also widely accepted that defaults matter and unless Signal makes an active effort to discourage people's default choice, the larger purpose of privacy will be somewhat defeated.
While the answer from most technical users will be "just switch keyboards", it's also widely accepted that defaults matter and unless Signal makes an active effort to discourage people's default choice, the larger purpose of privacy will be somewhat defeated.
[0] https://twitter.com/RealSexyCyborg/status/119769534457579929...