Hi,
The TextInput folder stores your personal dictionary of a shortcut for word and input pairs. When you use iCloud Drive the dictionary will sync across all your devices.
Check this help >> Use international keyboards
When using certain Chinese or Japanese keyboards, you can create a shortcut (text replacement) for word and input pairs. The shortcut is added to your personal dictionary. When you type a shortcut while using a supported keyboard, the paired word or input is substituted for the shortcut
If you use a Mac you can see contents of the TextInput folder with Terminal.app. The directory is the following: ~/Library/Mobile Documents/com~apple~TextInput/