How to change default_locale in Gettext

Hello,

I am supposed to create multi language website, therefore I am using gettext for this.
At first I created 3 language in my project and I made translations in it, but I couldn’t change default_locale like its document.

my project gited in GitHub - shahryarjb/ESOGTIPH: Easy sample of gettext in Phoenix 1.3 · GitHub

for example I have 3 lang ["ru", "en", "fa"]

my router :

  pipeline :browser do
    plug :accepts, ["html"]
    plug :fetch_session
    plug :fetch_flash
    plug :protect_from_forgery
    plug :put_secure_browser_headers
    plug SetLocale, gettext: MultiLangWeb.Gettext, default_locale: "fa", cookie_key: "project_locale" #cookie_key is optional
  end

  pipeline :api do
    plug :accepts, ["json"]
  end

  scope "/", MultiLangWeb do
    pipe_through :browser # Use the default browser stack

    get "/", PageController, :dummy
  end

and my project config :

config :multi_lang, MultiLangWeb.Gettext,
    default_locale: "fa"

As you can see, I changed fa insted of en in my config , but it allways loads en default .

How can I changed default_locale to fa or ru?

I had read (Translating Phoenix Applications with GNU gettext | Phrase),but there was no use for me .

please help me for changing it.

Thanks