You should not sign anything that you do not understand by 100%. Even if the contract is complicated, it should not be signed, if it wasn't checked by someone who at least translated it to you. You can also ask the landlord to send the draft of the contract to your email so you can read it or give it to someone who can translate it in advance. This makes it possible for you to ask the questions you have to the landlord. You can clarify your remaining questions with the landlord later.
There are two types of rental contracts.
Temporary lease contract:
It is legal to make a temporary contract. It could be that the house has to be renovated in two years and the apartment needs to be empty. That means the landlord would say, “during the two years, someone can live here but after that time everyone needs to get out.” In this case, a temporary contract is legal.
You can make a temporary agreement for other reasons too. But you need to know that there isn’t any protection when someone wants to end the contract. That means that when the time comes, you need to move out. At least if there was no agreement to extend the rental agreement. In this case, the landlord doesn’t need to write a notice. After the period it is over, one hands the key over and that’s it, not even a phone call to end it.
Permanent lease contract:
The contract usually contains the date on which the contract was signed and from when the contract is valid. It will say that the contract is for an unlimited amount of time. Below there is a section that says reasons why the contract could end. The main reason for one to end the contract is usually a delay in payment. If the rent is not paid for two months, the landlord can quit the contract immediately. That means it is very important to pay the complete rent on time!
What really needs to be mentioned in the contract are the signing partners, for example the owner and the adult renter. In the case that there are more adults, their names have to show up, too (partners or people in a shared flat). Of course things like when the contract began and when it ends (or that it’s a permanent lease) and also details about the apartment, like how many rooms, square metres, bathroom, kitchen etc. It should also inform about the quitting modularities, the amount of deposit you have to pay (Kaution) and an agreement about renovation. It is the standard way.
Everyone who is listed in the lease contract is entitled to live in the apartment, but must also pay rent. Every single person who is in the rental agreement is responsible for the entire contract. If your roommate or partner decides to move out without notifying you, then you still have to pay the entire rent.