Hmm my friend know my own language and english so he want to learn 1 more language so which you would prefer him german or french? I think german that it is better.
Tough one. German is spoken in many of the world's top economies including obviously Germany itself. French however is spoken in half of Africa, Canada and some parts of Asia too. While most of these are at the bottom of the 3rd world countries list, they can still prove to be important markets in the future.
Myself I'd pick German mainly cause of bias, but it would be a good option to know them both. Also in the EU French seems to be accepted as 2nd official language after English for some reason. Probably cause many of the institutions are located in Brussels which is a mostly French speaking town.
"German is spoken in many of the world's top economies" sorry but NO. German is spoken in Germany and Austria and in a part of Switzerland, even though it is so distorted compared to Hochdeutsch that it literally squeezes all the beauty out of the language. It is common to learn German in school in neighboring countries such as The Netherlands and Denmark, however this won't guarantee that you'll be able to stop people in the street and they'll automatically speak German, unless they live near the border.
If a person has a specific interest in a language for cultural reasons or because they plan to move there, they can learn any language they choose. If they're just looking for a language to learn that will be useful business-wise, well, between these two it would definitely be French because:
1) French is spoken in a variety of countries in Europe + Africa and Canada and former colonies overseas.
2) French has historically been the diplomatic language in which foreign delegations used to communicate to each other. Most words that describe governmental positions and organization have been directly borrowed from French
3) French are very proud of their language and have not taken well to English replacing it as The international language. Jacques Chirac was the first French president to ever have spoken English in public and this caused a bit of a stir with the public opinion: not because previous presidents didn't understand English but rather because the French always expect others to speak their language and not the other way around. I have worked with many clients with whom this was consistently the case. Hence: whenever you work with French clients, be prepared to speak their language. And you'll be better off this way since they have such a thick accent that they would make most languages they attempt to speak almost incomprehensible. Germans, on the other hand, are not so precious and are happy to speak English.
Basically: unless you have a specific preference for one of these two languages or cultures, go for French. If you're looking for an even more useful language, opt for Spanish.