One nature of learnining foreign language

I found one thing about learning foreign language. And this will alarm the trend going on in Japan that is learning English is something proud of, or that will brings you something valuable. There are so many people learning English for ambiguous things.
The assumption is that we all human have almost the same world of meaning. We have something to tell and mean in our mind. And language is about how well that can tell to the others. If you are fluent enough to tell what you have 100%, the language is supreme. This is true for native language of people. Maybe not 100%, but around 90% to 99% of course. And if you use foreign language you are not familiar, say you only know how to say "Hello", the rate the language can tell what you have in mind is almost 0%!! And learning foreign language can be seen as heighten the rate from 0 to certain amount. You can't heighten it over 100%. This is the point. Language is just a tool to tell what you have or get something that you can reach using language. Make no mistake that just learning English won't bring anything special. There are so many people speaking English just have born in English-speaking countries. We learn English just because it became the lingua franca, we just want to take advantage of using English.