$ sudo apt-get update
$ sudo apt-get install fcitx-unikey 

fcitx-unikey is installed in your system.

Make ensure the fcitx-unikey package were installed using the commands given below,

$ sudo dpkg-query -l | grep fcitx-unikey *

You will get with fcitx-unikey package name, version, architecture and description in a table

fcitx-unikey package basic information: