TITLE: What are good non-English languages for mathematicians to know?
QUESTION [49 upvotes]: It seems that knowing French is useful if you're an algebraic geometer.  More generally, I've sometimes wished I could read German and Russian so I could read papers by great German and Russian mathematicians, but I don't know how useful this would actually be.  What non-English languages are good for a generic mathematician to know?  Are there specific languages associated to disciplines other than algebraic geometry?  
(This question is a little English-centric, but I figure it's okay because this website is run in English.)

REPLY [13 votes]: I not a native  English  speaker  and thus my intervention here is a bit odd, to say the least. Growing up behind the Iron Curtain I learned English, but I discovered that as a  mathematician  it is more useful to learn Russian,  simply because the Soviets translated  all the influential books and articles into Russian. Often, the Russian translations would be better than the original because the translators,  influential mathematicians themselves, would correct possible errors and would add illuminating footnotes and appendices.
To this day I cannot read German, but I can read Grauert's or Brieskorn'article in Russian. Today though, English is the lingua Franca of  Science, so for a youngster it is more profitable to concentrate on Math.