I guess all smartphones requires a hot spot to connect to the internet.

Is it possible to add an aircard to be independent from hot spots?

No. All smartphones are phones so have 3G or Edge connection.

Sorry for my naivity. If on travel route in Europe/Germany and I don't want to search for hot spots, which I understand makes the connecting time cheaper, but want to have direct internet access on my new android what is needed?

Special sim cards, contracts?

Make sure that your SmartPhone can communicate with the 3G networks in those countries. Then do a little research as to whether you can obtain prepaid SIM cards for your stops.

Example