Here's another perspective on which foreign language(s) to learn: learn the ones which bring you the most potential for love, fame, inner peace and all-round improvement in your life!
There's this astrological technique called AstroCartoGraphy where by relocating to another place, you change your life. For example, you want fame in your profession. Move to a place which sits on your say "Sun MC line" e.g. Beijing in China. What if you can't relocate to Beijing for whatever reason? Based on my experience, it seems to me that interacting with people from or near the place i.e. Beijing or doing business in or near to Beijing would also boost your reputation. So, if you would like to up your fame, you might consider learning Mandarin.
Well, that's the general concept although in practice, there are more factors to consider before you enroll for that Mandarin class. There could be different parts of our psyche that promote or inhibit us from shining and thereby gaining the recognition and fame that we seek. For those bits that inhibit us from expressing our self-identity and shine brightly, unless we have consciously worked to integrate them within us, they will continue to have their effect on us regardless where we go, do or speak. So, yeah, go learn Mandarin and also do some work on yourself to maximise your chances of fame in the whole wide world.
On the other hand though, if you can devote the energy and time to learn a foreign language, why not use that on yourself, to work through the kinks within you? When you have done that (although being whole could take a few lifetimes), it could be the case where you decide that there's no real need to learn a foreign language anymore.
Cosmic Insights for an Even Better Life