How can I change the collate of database in AgensGraph (under Windows OS)

Question

I want to deal UTF-8 format data using AgensGraph under Windows operation system.

AgensGraph is based on Postgres. Therefore I think that if I declare the LC_COLLATE of database as 'en_US.utf8', then I'll be able to deal UTF-8 format data.

e.g.CREATE DATABASE DBname LC_COLLATE 'en_US.utf8';

However I faced the error code.

ERROR:  invalid locale name: "en_US.utf8"

So how can I know, what locale will be declared under Windows operation system?