Devise "is a flexible authentication solution for Rails based on Warden". Internationalization (aka i18n) is a "means of adapting computer software to different languages, regional differences and technical requirements of a target market". Devise supports i18n in controllers, models, and in other areas, but it does not have support for internationalized views. devise-i18n adds this support. Devise also does not include the actual translations. devise-i18n does this too.