wicked pdf does not render UTF-8

Unicode characters does not render properly when generate pdf using wicked pdf. There are 3 steps need to follow:

1. Set encoding: 'utf8'

render pdf: "myfile",
       ....,
       encoding: 'utf8',
       ...

1. Make sure to render proper meta tag in layout template

%meta{:content => "text/html; charset=utf-8", "http-equiv" => "content-type"}
%meta{:charset => "utf-8"}

1. Install system fonts

apt-get install fonts-khmeros