locale-gen: not found when running docker build

[tkda-h3]

$ docker build .

Step 3/16 : RUN locale-gen en_US.UTF-8
 ---> Running in XXXXXXXXX
/bin/sh: 1: locale-gen: not found
The command '/bin/sh -c locale-gen en_US.UTF-8' returned a non-zero code: 127

I think I have to run 'apt-get install locale' like this question