Which languages are preferable to study for a mathematician?

I am already fluent in portuguese and english, and I can also read spanish well. I have to read a text which is in french, and I'm having some difficulties. Knowing that there are a lot of people out there in the field of mathematics that are able readers of several languages, I would like to get the opinions of more experient professionals about their own experiences with different languages and from which ones they get/got more benefits from.

I intent to use these opinions as a guide to choose the next language I will learn how to read, if not everything, at least mathematical texts. My initial belief is that I will get the most beneficial experience by learning french and then german, but I'm not sure; I never had experience to acknowledge mathematical texts in more strange languages (although once I started trying to learn korean - gave up some weeks later for lack of time).

Opinions?

A language not mentioned yet is Russian. During the Cold War era, a lot of great papers have been written in mathematics, physics and other scientific disciplines by Soviet mathematicians and scientists and were only later rediscovered by Western mathematicians and scientists. The conclusion was that especially in the fields of mathematics and physics, the Soviets had developed many of the important 20th century results independently. That and there are also many classics by Russian authors (Kolmogorov, Landau & Lifschitz,...) some of which are translated, others not. Who knows what gems are still laying in wait?

As a German native speaker who also knows English and French, I have the impression that you will get more mileage from French than from German with regards to mathematics. The situation would be different with respect to philosophy. However, I would advice against trying to read "famous" French works like those of Bourbaki or Grothendieck. I like the honest and direct way of writing those French texts often have, compared to the overly exact and philosophical tone often present in German works. Take Bernhard Riemann or Felix Klein as examples, compared to René Descartes, or the following quote from Jean Fresnel's book "Méthodes modernes en géométrie":

il ne faut pas se faire d'illusions, Descartes résout des problème de géométrie, non parce qu'il a de la méthode, mais parce qu'il a des idées

(Rough translation: "don't expect too much, Descartes solves geometric problems because he has ideas, not because he has a method".)