html-pdf fontconfig warning: ignoring utf-8: not a valid region tag

[suda...@freolabs.com]

Hi,

I am first here, I have an issue with html-pdf npm . It always throws the error says as follows: "html-pdf fontconfig warning: ignoring utf-8: not a valid region tag" And iam having a ubuntu server 16.04.1. initially i had following locale : 

LANG=C.UTF-8
LANGUAGE=en_US.UTF-8
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=en_US.UTF-8

got stuck here.How to solve this issue ?

Thank you in advance