Install Chinese Input on Ubuntu 20.04

1. Settings / Region & Language / Input Sources / Manage Installed Language

    Add Chinese

2. Settings / Region & Language / Input Sources / + 

    Select ... , 

    then Other, 

    then select Chinese, Press Add

3. Settings / Region & Language / Input Sources / Chinese

    Press Chinese, Select Chinese (Chewing)

VirtualBox Copy & Paste don't work between host and guest OS (for Ubuntu)

Refer to https://askubuntu.com/questions/63420/how-to-fix-virtualboxs-copy-and-paste-to-host-machine

1) VirtualBox / Machine / General / Advanced

    Shared Clipboard: Bidirectional

            Drag'n' Drop: Bidirectional

2) The guest's Ubuntun terminal commands:

sudo apt install virtualbox-guest-x11 --reinstall
VBoxClient-all --clipboard

I used --reinstall option because of I had virtualbox-guest-x11 package installed and before reinstalling it I had:

$ VBoxClient-all --clipboard
VBoxClient: error: No service specified. Quitting because nothing to do!

3) After reboot screen resolution jumps to its minimal value, so

Run Guest OS (Ubuntu) / Settings / Displays / Resolution