How to quote a non-English quotation in dissertation? I am writing my math PhD in Berlin (Germany) in the English language. 

I would like to cite a German quotation from a famous mathematician as a start of my first chapter.

Should I quote it in the original language and make a footnote of what it means in English, or should I freely translate it into English without a footnote? Or is there simply no standard for this kind of fancy quotations?
The quotation is really more for fun than for substance, so you've got a lot of leeway, and even more so because this is in a Ph.D. thesis.  So really, it's up to you whether you translate it at all.  

That said, I would suggest approaching it based on the degree to which you like the prosody and meter of the quotation.  If the sound of the words themselves is a significant part of what makes you enjoy the quote, then by all means keep it in the original language, where it will be well appreciated by some readers and challenge the rest.  If the substance is more important than the sound, then it may be better to translate.

For example, I don't know much of German quotations, but if I were using a French quotation, then I would not translate "Ceci n'est pas une pipe," but I would definitely translate "Les grandes personnes ne comprennent jamais rien toutes seules, et c'est fatigant, pour les enfants, de toujours et toujours leur donner des explications."