class ApplicationController < ActionController::Base
  protect_from_forgery
  rescue_from ActionController::RoutingError, with: :not_found

  before_action :set_locale

  def authenticate_admin!
    return if current_profile && current_profile.admin?

    redirect_to profiles_url, notice: I18n.t('flash.profiles.no_permission')
  end

  def after_sign_in_path_for(resource)
    profile_url(resource) || root_path
  end

  def render_footer?
    false
  end

  helper_method(:render_footer?)

  private

  def build_missing_translations(object)
    I18n.available_locales.each do |locale|
      object.translations.build(locale: locale) unless object.translated_locales.include?(locale)
    end
  end

  def set_locale
    desired_locale = request.headers['HTTP_ACCEPT_LANGUAGE'].to_s[0..1] == 'de' ? 'de' : 'en'
    I18n.locale = params[:locale] || desired_locale
  end

  def default_url_options
    options = super
    options.update(locale: I18n.locale)
    options
  end

  def not_found
    render plain: "404 Not Found", status: 404
  end
end

class ApplicationController < ActionController::Base
  protect_from_forgery

  before_action :set_locale

  def authenticate_admin!
    return if current_profile && current_profile.admin?

    redirect_to profiles_url, notice: I18n.t('flash.profiles.no_permission')
  end

  def after_sign_in_path_for(resource)
    profile_url(resource) || root_path
  end

  def render_footer?
    false
  end

  helper_method(:render_footer?)

  private

  def build_missing_translations(object)
    I18n.available_locales.each do |locale|
      object.translations.build(locale: locale) unless object.translated_locales.include?(locale)
    end
  end

  def set_locale
    desired_locale = request.headers['HTTP_ACCEPT_LANGUAGE'].to_s[0..1] == 'de' ? 'de' : 'en'
    I18n.locale = params[:locale] || desired_locale
  end

  def default_url_options
    options = super
    options.update(locale: I18n.locale)
    options
  end
end

--- 
+++ 
@@ -1,5 +1,6 @@
 class ApplicationController < ActionController::Base
   protect_from_forgery
+  rescue_from ActionController::RoutingError, with: :not_found
 
   before_action :set_locale
 
@@ -37,4 +38,8 @@
     options.update(locale: I18n.locale)
     options
   end
+
+  def not_found
+    render plain: "404 Not Found", status: 404
+  end
 end
Add a 404 not found error message so the logs are more clean
