I have attached a demo video for the bug. The test case starts with a setting: In adobe acrobat pro preference, I switched the application language from English to Simplified Chinese.
After that, in a random pdf file, under Fill&Sign tool, if I start to type in Chinese characters, the input isn't successful. Otherwise, if I type in some signs in Chinese, such as a comma or a question mark, input with Chinese afterwards works.
Basically I think the missing function here is that it cannot detect Chinese Font automatically to initiate a Fill&Sign input.
Details please check the video attached. Thank you.