Add flash message translation for log out

app/controllers/spree/user_sessions_controller.rb

@@ -45,6 +45,7 @@ module Spree
       # Logout will clear session data including shopfront_redirect
       #   Here we store it before actually logging out so that the redirect works correctly
       @shopfront_redirect = session[:shopfront_redirect]
+      flash.notice = t('devise.sessions.signed_out')
 
       super
     end

config/locales/en.yml

@@ -159,6 +159,8 @@ en:
       already_registered: "This email address is already registered. Please log in to continue, or go back and use another email address."
     success:
       logged_in_succesfully: "Logged in successfully"
+    sessions:
+      signed_out: "Signed out successfully."
     user_passwords:
       spree_user:
         updated_not_active: "Your password has been reset, but your email has not been confirmed yet."