I chose to highlight the Chinese aspect, but you're absolutely right: any keyboard with personalisation puts Signal users at risk.
> ... please use the original title, unless it is misleading or linkbait; don't editorialize.
https://news.ycombinator.com/newsguidelines.html
If you can still edit the title, you should change it to the original "Signal should warn users who are likely using insecure IME apps"