I've been studying a few languages using Duolingo for about the last two years and I'm starting to think if I truly knew 50 words in the world's top languages I would be able to pretty much understand any conversation anywhere.
I'm a native English speaker and have some experience speaking Spanish while I lived in Honduras for two years but I've been studying German, French, Italian, Portuguese and Russian somewhat simultaneously (I usually do two lessons a day in whatever language I feel like studying that day).
I knew going into this that I would gravitate to the Romantic languages so obviously I was going to see similarities in those languages, but as I studied the etymology of words I got the sense that even languages that are seemingly unrelated, come from a common root and that there are patterns for how words change over time and distance from their origin.
So far I've only delved into Indo European languages but my very cursory understanding of other language families suggests they develop the same way (I plan on learning Chinese and Arabic as soon as Duolingo gets them ready :)).
So, what is the pattern? Well, I don't fully know, but I think a part of it lies in how ideas are understood and recognized in the human brain. And when we fully understand the way ideas are recognized and stored in our brains we'll know how they are transferred from one brain to another.
Right now, though, my theory is that if I learn 50 words in the world's top languages - and I mean really learn these words such that I know their etymology, can recognize them being spoken in whatever context (speed, accent, quality, conjugation, etc) and can speak them readily - then I think I will be able to understand pretty much any conversation anywhere and even begin to understand old or obscure languages without any prior study.
Why? Because I think that all languages and ideas have a common thread or root. I'm going to call that thread or root a spirit because it fits most easily with my understanding of human existence. I don't think there is a beginning or end to our spirits, they have always existed and will always exist (at least from our temporal reference on this earth). When a person is born (and this happens gradually) it is literally the separation of a spirit from a spirit/root. We forget the connection we have to all other spirits (or maybe better said, The Spirit, since more than one spirit suggests separation as well) and therefore become finite and temporal. If we were to remember (which is really the process of diminishing our separation from knowledge) then we wouldn't be finite, we'd be fully connected to the Spirit. So, when we discover how an idea is recognized (and I say recognized rather than created because for an idea to actually be a root/spirit it must have always existed and therefore never have been created) we will remember its root and since all ideas have the same root, we will unite ourselves with The Spirit and lose multiplicity, time, and distance. I think in order for this truly to happen, though, you'd have to lose every separation, and therefore every imperfect notion, otherwise there would always be separation and confusion as to the true root/Spirit.
So, basically, I'm saying that if I study and have 50 words well understood in the world's top languages, I will have the gift of tongues and be able to communicate to anyone through The Spirit.