How does anyone learn English as a second language?

It's not just that the language is filled with words that look absolutely the same but are pronounced differently--I read for pleasure; I read the book--or words can mean two different things that are contradictory (inflammable, for example). But I was recently struck by a phrase I've heard all my life and realized it had two seperate meanings and only context to set them apart.
The phrase is, "The die is cast." For me, the meaning is that someone has rolled the dice and made a decision. But I recently went to a printing museum where the docent, as part of the spiel, actually showed the crowd how a particular letter was cast into metal. "The die is cast."
These are the thoughts of a word snoot.