This is a basic step required for enabling multilanguage installations. There's been quite some discussion inand now in .
Creating a multilingual installation profile that enables the right modules and perhaps tweaks other things here and there is a good thing UX-wise (so that site builders don't go pogo-sticking after installation), but we first and foremost need to have a multilanguage site in place to begin with.
So, what needs to be changed is to allow the user to select multiple languages during installation. Having the drop-down language selection menu be a multi-select widget instead would do it, but having to ctrl+click or shift-click is not good UX. What if we kept the drop-down as is but added a "Add another language" button? This would trigger a multilanguage site installation with some additional steps (TBD).