My reasons for not selecting Spanish and German are as follows:

1. German. German is the least useful of the three languages you mentioned. There are fewer and fewer scientific papers being written in this language and most of the philosophical works written in German are fairly clearly translated into English (i.e., it's not like trying to translate philosophy from Chinese to English). German is not widely spoken outside Germany, Austria or a few other places, and even then the dialect differences between Swiss German and High German make understanding difficult at times. Finally, even in terms of traveling, enough Germans speak English fluently that there is no need to learn German to enjoy Germany. Unless you're (1) dying to read, say, Heine's poetry in the original German or (2) planning on studying German history for a living, German scores a big round zero by nearly any other criteria.

2. Spanish. Spanish certainly has the utility (though that part about the Amazon is incorrect - they speak Portuguese in Brazil). It is the first language of the overwhelming majority of countries in the New World south of the United States. Dialect differences are usually small enough that someone who knows Castilian Spanish can understand the others. However, I think that it compares unfavourably with French when we review the corpus of literature written, the history of the language and its impact on the world. In literature, Spanish-language authors are easily eclipsed by French-language authors. In scope of language penetration, French is spoken in many more parts of the world (i.e., if you don't want to go to Latin America, forget Spanish). Sure, people will try to argue that there is Spanish influence in the Philippines, but those people have obviously never been there (I have and can tell you that your Spanish will help you not one bit). In the sciences, Spanish is not used on an international basis.

Ultimately, French is a language of culture and civilisation. Yes, it may not have as many speakers worldwide as Spanish, but those speakers are represented on nearly every continent. A significant number of people in Vietnam, Canada, French colonies in the Caribbean region, Africa, the Middle East and elsewhere speak French as a second language. French literature is perhaps the finest the world has known (after Russian, of course ). The cultural influence of French civilisation is unmistakable and overwhelming.