Extract choose_locale method, similar to CodeHarbor

app/controllers/application_controller.rb

@@ -158,9 +158,29 @@ class ApplicationController < ActionController::Base
     response.headers['X-Content-Type-Options'] = 'nosniff'
   end
 
+  def sanitized_lti_locale_param
+    sanitize_locale(params[:custom_locale])
+  end
+
+  def sanitized_locale_param
+    sanitize_locale(params[:locale])
+  end
+
+  def sanitized_session_locale
+    sanitize_locale(session[:locale])
+  end
+
+  def choose_locale
+    sanitized_lti_locale_param ||
+      sanitized_locale_param ||
+      sanitized_session_locale ||
+      http_accept_language.compatible_language_from(I18n.available_locales) ||
+      I18n.default_locale
+  end
+
   def switch_locale(&)
-    session[:locale] = sanitize_locale(params[:custom_locale] || params[:locale] || session[:locale])
+    locale = choose_locale
-    locale = session[:locale] || http_accept_language.compatible_language_from(I18n.available_locales) || I18n.default_locale
+    session[:locale] = locale
     Sentry.set_extras(locale:)
     I18n.with_locale(locale, &)
   end