It's not remotely a realistic option. CJK is all second class citizen. I just tried their latest demos. Tried to enter 日本. It utterly failed. First it's still trying to draw on it's own so you get to see some placeholder □ while typing. Then, it effup and typing n-i-h-o-n kept producing Nいほん on this example

https://gallery.flutter.dev/#/demo/cupertino-text-field

As long as they keep insisting on rendering everything themselves instead of relying on the OS/DOM Flutter will always be a poor choice for UI