Visibility and Signup / Translation (in general)

Hello there,

as can be seen on the screenshot I have got two specific questions, please.

1. (red arrow) Why does it not say by whom the article was posted.

2. Frontend: I can now find my listings and edit them and so on… but how can other users log in / register in order to post on their own?

And one general question: I now understand that there are translations to most of the wpmu plugins. So the directory plugin is not fully translated into German. How (or better: where) can I continue translating so that I have the words and phrases (orange arrow) in German (in my case).

And can I let the user switch frontend between English and German?

Thanks a lot for helping,