I think you're greatly overstating the usefulness of French; I've noticed that French-speaking people seem to have this misconception about the importance of their language, not grasping that it's no longer the late 1800s or early 1900s. French is only widely spoken in former French colonies, which are all generally economic backwaters (which probably has a lot to do with how poorly France treated its colonies). I'm not aware of any significant parts of South America where you can speak French, outside French Guyana: anywhere else, and you need to speak Spanish or Portuguese, though you might be able to get by with English just due to its popularity as an international language (which French is not).

French might be "official" in Belgium and Switzerland, but that's about as useful as it also being "official" in Canada. Good luck speaking French to people in British Columbia or Alberta; only people in Quebec speak it. The same is largely true in Belgium or Switzerland: go outside the French-speaking area and you're going to have trouble. Luxembourg is a micronation.