Mysterious Language
You meet an ominicient god. He understands English perfectly and he knows everything, but he will only answer yes/no questions. Furthermore, he will only ever answer in his own language, and his possible answers are "da" and "ja", though you aren't sure which one means "yes" and which one means "no". However, he always answers truthfully.
Say you would like to know if the Riemann Hypothesis is true. You are allowed to ask this god one question. What do you ask?