Before you leave, get an International Drivers License (IDL) for yourself. You can't get an IDL after you have left the USA. When you get to Europe the motorcycle will need to be registered/licensed with one of the EU countries, typically the country where the motorcycle reaches it's destination from the USA.
When I travel over seas I get an IDL from AAA. But there are other resources if you are not an AAA member.
http://www.idlicense.com/