mba07 - I was having a laugh. Sorry, my sense of humour is typically quite dry, and doesn't really transfer to the web well. Consider me chill, but now trying to make some sense from my leaden-in-sarcasm post.
Really, German is the most spread (by country) European language. You have Germany, Austria, Switzerland. You can easily get by with German in Poland, Holland, Belgium, and others. Compared to French, it is a highly industrialised coverage. Only in recent years, when Europe has become more considered about the existence of South America, has Spanish and Portuguese become considered as a reasonable language.
The knowledge of German industry is a more honest one. If you think of how many companies there will be working on domestic industry or raw material in any country, then see a bit of the Rhein belt, you will understand that you could have a very fruitful career as a consultant without really every going East of Bern. I don't know US territories to compare too well, but parts of Germany don't look unlike Gary, Indiana. Germany is hugely industrialised - in fairness if you want me to, I will dig out some statistics on how big an economy (industrialwise) it is, but if you are happy to take my word, it will save me some time to research other things (I am finding I should research my blogposts, forumposts and everything much more nowadays, and there is only so many hours in the day).
Necro is right in part, that English carries as the common language. My nation has made a lifetime of laziness on accepting this as fact. That said, many companies in interaction, and especially on offering consultancy, would be likely to feel that being able to relate in their mother tongue is a big advantage (and I can't see how this would be a surprising ascertion). There is a pressure that, if you are being paid by a client, you should meet their needs. Only if you are somewhat informationally superior can you do otherwise, and for McK there is Bain and BCG competing, so this is not the case. Ergo, you offer communication in their language to try and get closer to the deal.
Esperanto was a terrible attempt at a linguistic Euro (I am more tempted to write ECU, as that gives its time more clearly). Some people do speak it, but more out of irony than anything - it was never taught, least not in my time. Fundamentally a crazy idea.