diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 5a3b513..5dc8755 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -4,6 +4,7 @@ class ApplicationController < ActionController::Base
   protect_from_forgery with: :exception
   helper_method :current_user
   before_action :login_required
+  before_action :set_locale
 
   def current_user
     return unless session[:remember_token]
@@ -20,4 +21,29 @@ class ApplicationController < ActionController::Base
   def find_fluentd
     @fluentd = Fluentd.find(params[:fluentd_id])
   end
+
+  def set_locale
+    available = I18n.available_locales.map(&:to_s)
+    if params[:lang] && available.include?(params[:lang])
+      session[:prefer_lang] = params[:lang]
+      I18n.locale = params[:lang]
+      return
+    end
+    if session[:prefer_lang]
+      I18n.locale = session[:prefer_lang]
+      return
+    end
+
+    # NOTE: ignoring q=xxx in request header for now
+    return if request.env["HTTP_ACCEPT_LANGUAGE"].blank?
+    langs = request.env["HTTP_ACCEPT_LANGUAGE"].gsub(/q=[0-9.]+/, "").gsub(";","").split(",")
+    prefer = langs.find {|lang| available.include?(lang) }
+    unless prefer
+      if langs.find{|lang| lang.match(/^en/)}
+        I18n.locale = :en
+        return
+      end
+    end
+    I18n.locale = prefer
+  end
 end
diff --git a/config/application.rb b/config/application.rb
index 587534a..939f684 100644
--- a/config/application.rb
+++ b/config/application.rb
@@ -30,7 +30,7 @@ module FluentdUi
 
     # The default locale is :en and all translations from config/locales/*.rb,yml are auto loaded.
     # config.i18n.load_path += Dir[Rails.root.join('my', 'locales', '*.{rb,yml}').to_s]
-    config.i18n.default_locale = 'ja'
+    config.i18n.default_locale = 'en'
     config.autoload_paths += %W(#{config.root}/app/workers #{config.root}/lib)
     config.after_initialize do
       # http://qiita.com/tanaka51/items/c8873319689217bb81a9