Tenure possibilities for junior professorship I have read whatever I could find online about W1 (junior) professorship in Germany, and to me it seems it is somewhat close to a full time lecturer and the tenure possibilities are slim if none, all the more slimmer at the same university. However, the person who has invited me for an interview said this is rather because they are legally required to do so, but there are tenure possibilities. I will ask him for more information, but 1. I do have a tenure option at other university (and another country), however the university is not at all in a good ranking, I also have an invitation from a couple of really good universities but I will need to decide soon so I don't know if I will be able to act upon those. 

First things first, I don't want to be a lecturer - meaning that I don't want to focus on coursework but research, I heard that junior professors can have students and a research group? But they also teach a lot of entry level courses? so what are these "tenure possibilities" exactly? Does he mean a remote possibility in 6 years? Or does he mean somewhat something close to a tenure-track? What are tenure chances?
It depends: There are W1 professorships with a tenure track, and there are those without. If there is a tenure track, then that is usually prominently advertised, and more importantly, in writing. If there is nothing about tenure in writing, then the safe assumption is that you won't get tenure, and you will have to leave after 6 years. Verbal assurances that you might get something aren't worth much.

As to the teaching load, there are those that focus on allowing the person to qualify for a "real" professorship (W3), i.e. either as an alternative to a Habilitation or as a possibility to write your Habil. There are others were the position is used as a form of cheap labor for teaching. W1 positions with tenure track tend to fall in the first category, but there are also W1 positions without tenure track that fall in the first category. In that case, the W1 position is a stepping stone that helps getting a W3 at another university. Again, if it is a W1 aimed at allowing the inhabitant to qualify for a W3 professorship, then that is prominently mentioned and in written form. Only verbal assurances would make me worried.

If you know someone who work at a German university that you trust, you may want to let that person have a look at it. For an outsider it can be hard to read between the lines.