Can I use Baby George Roaster Oven GR59A in German electrical system ?

There is no electrical standard used in more than a couple of countries. Voltages differ, outlets differ, and there are a few surprises wherever you go. If the oven is made for the USA market it will have a tag that specifies the voltage and power requirement. Then you have to check the plug to see if it fits your outlets. You can use google.com to find manuals for most appliances, like this: www.useandcaremanuals.com/pdf/GR59A.pdf