Install Ibus-unikey in Linux for Vietnamese

Uninstall all preinstalled ibus package and its dependencies

    sudo apt-get remove --auto-remove ibus

Purging config/data too

    sudo apt-get purge --auto-remove ibus

Maybe restart is needed.

Install new ibus-unikey

    sudo apt-get install ibus-unikey

After installing done, run:

    ibus-setup

to open Ibus Preferences. 

Choose Input method tab, check 'Customize active input methods'. In selection box, click Show all input methods, choose Vietnamese->Unikey.

Logout your system to active the new input method.

Now in top right corner of your screen, you are able to select 'Unikey' to input Vietnamese.