Right now, adding in new languages is not user-friendly if they do not have their own Wikipedia, even in the incubator, or if they haven't started translating the UI. This is one issue preventing under-resourced language communities from being able to participate in projects like Wikidata and Commons, which are not as work-intensive for these communities to create and maintain and many language communities will, in reality, never have a Wikipedia of their own. This does not mean that they do not have knowledge to share and they shouldn't be prevented from sharing it.
For example, the possibility of adding labels and descriptions to items without having to have the UI translated is, AFAIK, not possible, yet this would let these communities share their knowledge with the resources they do have.
So I would like to gather thoughts related to how to do this without needing an up-and-running Wikipedia and I will divide it into subtasks.