Save user locale and use it to translate things

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/mobilizon_web/views/email_view.ex

@@ -1,6 +1,8 @@
 defmodule MobilizonWeb.EmailView do
   use MobilizonWeb, :view
 
+  import MobilizonWeb.Gettext
+
   def datetime_to_string(%DateTime{} = datetime, locale \\ "en") do
     with {:ok, string} <-
            Cldr.DateTime.to_string(datetime, Mobilizon.Cldr, format: :medium, locale: locale) do