When traveling through Europe - excluding Russia, which is not a part of Europe per se - if you want to learn a second language in order to get around easily, I recommend German. More Poles, more Czechs, more Slovakians, more Romanians, more Hungarians, more Croatians, more Serbs, speak German as a second language than speak Russian.
German would come in handy because it's also widely used in the Scandinavian and Low Countries.
However, if you're going to be spending more time in Russia, Latvia, or Estonia, or the Ukraine, or Belarus, I recommend Russian as the language to learn.
French is basically useless in Eastern Europe and not widely used in the Scandinavian, Germanic, or Low countries.
The numbers for French speakers are skewered in a sense because many of those who speak French are not in Europe at all, while most who speak German do live in Europe. The numbers for French speakers (as a first language) include Canadians, and former French colonies in Africa and other places far flung from the Motherland.
The question was - French or Russian? I recommend Russian or German, depending on the area one plans to travel most extensively. But if you're expecting Poles and Czechs and Hungarians to speak Russian, you're in for some frustration. They hated being part of the Soviet bloc and have done all they can to distance themselves from that part of their history, including ditching the language. But there are so many ethnic Germans throughout that part of Europe that German has hung on (also due to Germany's economic powerhouse in that region).