Over the years, what language was spoken at the International Mathematical Congress? I assume it is English right now, but it was founded by two German mathematicians, so I assume the language was German once, especially since Göttingen (Germany) was the mathematical center of that time. Is this true? If so, when and why did it change form German to English?
Note: I've written an own answer to this question lately, using the links and information others provided in answers.