How lang may my internship last ?
With a J1 visa you can stay for a maximal duration of twelve months.
Am I allowed to extend my internship in the USA ?9
Yes, if your original internship last not longer than twelve months it is possible to extend the internship up to a duration of twelve months.
Am I allowed to do other jobs while the internship?
No, strictly forbidden to do other jobs while the internship
Which informations do I have to keep ready for the entry in the USA ?
You need availible entry document if you want to go to the USA (e.g. passport) moreover the flight passenger have to know at least the adress of his first place he want to stay in the USA. The airline entitled to transmit the dates to the US public authorities already before the arrival of the passenger in the USA?
Do I need a credit card in the USA ?
Credit card payment is widley spread in the USA. Almost every kind of credit card and EC/Mastercard are accepted in the USA. To pay with an ec-card is unusual but
Can I drive with my german driver licence in the USA ?
In general yes, but in some federal states you need an extra internationla driver licence. Moreover you have to inform about the US traffic rules. In particular the US speed limit is not so high as the german and transgressing there could be really high forfeits.
Is my identification card accepted in the USA?
No the only official document that is accepted in the USA is your passport.