I don't think that you have to become fluent for the Grand Ecole program. Some level of French would be a plus, though. In terms of living or getting around, everything was fine for me. I know basically nothing when it comes to French. I wanted to learn, but had no free time.
For working in France, though, you would need a very high level of French language skills. And to be honest, nobody in this situation could learn the necessary amount in two years. Fortunately, a number of internships don't require French.
The job market is bad everywhere in the West, so you will face some challenges there. HEC has a pretty good placement record, which is a plus.
Having a quantitative background, or at least the ability to think in those terms, is definitely a plus for finance. It's even more so for the MMFE.
I don't know too much about the above-mentioned St. Gallen degree (I applied to the MIF, though). This school's strength is felt mostly in the Germanic areas (Switzerland, Germany, Austria, Liechtenstein).
I have no idea why the placement report is two years old.