Not sure if this is the best place to have this discussion, but anyway.
Working with localisation firms, inviting the translator to the admin is not at all a good solution. They need a file that they can import to their translation software, where they keep market and client specific dictionaries to quickly translate common terms and phrases. And also make the language consistent overtime (so ex a certain custom hardware tool is named the same among all pages for that language).
They will also need to be able to see what has updated, and in what context it exist, ex a PDF of the page it exist on.
Other missing features in the localisation plugin is the ability to sync changes from the default language. Ex if you add a new component, or update an image, you need to be able to sync that change (with a manual review) to all other localisations.
It would also be beneficial to be able to select multiple languages for a page. Ex a page in Spanish could have both Spanish (Chile) (es-CL) and Spanish (Spain) (es-ES). Sometimes the content could differ due to being different markets, but most of content can probably be shared among the two different locales.