How can I install one language by command-line

For desktop you can

sudo apt-get install language-pack-[cod] language-pack-gnome-[cod] language-pack-[cod]-base language-pack-gnome-[cod]-base 

But each applications can have its language pack. To know the packages to be installed try:

check-language-support -l [cod]

For example:

check-language-support -l fr

Auto install all dependecies:

sudo apt-get -y install `check-language-support -l fr`

where fr is the desired language code.

First, you need to edit the locale.gen file.

sudo vim /etc/locale.gen

Then looking for the language pack you need and remove the comment mark, for example, if I want to install zh_CN.GBK GBK zh_CN.UTF8, I just remove the # symbol in these lines, alternatively, you can also add your lines directly into the file. Finally, run:

sudo locale-gen

This is the simplest way I found online.