Its a very strange story about this job offer, specialy as it is compeletly out of the requirements that LH and 4U usualy have.
Just about the salary, you will end up with around 5000€ gross, as the job is quite interesting for those without job in germany, they have to pay tax in germany and will end up with around 3500€ and still have to pay for the medical insurance. It will pay your bills, but not so good for a short time contract.