LET'S START with these two basic questions.
I'll begin with the second because it's easier to answer.

We should learn languages because language is the only thing worth knowing even poorly.
If someone knows how to play the violin only a little, he will find that the painful minutes he causes are not in proportion to the possible joy he gains from his playing. The amateur chemist spares himself ridicule only as long as he doesn’t aspire for professional laurels. The man somewhat skilled in medicine will not go far, and if he tries to trade on his knowledge without certification, he will be locked up as a quack doctor.

Solely in the world of languages is the amateur of value. Well-intentioned sentences full of mistakes can still build bridges between people. Asking in broken Italian which train we are supposed to board at the Venice railway station is far from useless. Indeed, it is better to do that than to remain uncertain and silent and end up back in Budapest rather than in Milan.

- Polyglot: How I Learn Languages, Kató Lomb