The most difficult part of learning any language is the language colloquialisms.
"I got run over" might mean that "I was confused considerably by it" or "It was over my head" or "It was difficult to grasp or understand."
In German, one might say "Ich steige auf die Beine" which literally means "I climbed up on my legs", but means, I got up or woke up and got out of bed." "Er hat a sehr lange Leitung" literally means "He has a long wire", but colloquially, means "He's stupid and doesn't ever get the idea." It's about the same as in English, saying "He's off planet, in orbit around Mars or in outer space." Saying in English that somebody is zoned, means that they are stunned, catatonic, lost their mind or drifting.
New colloquialisms arise all the time in all languages and contribute to their continuing evolution. Some of the most interesting colloquialisms involve God, to avoid blasphemy or sex, sexual organs and ludeness to avoid being guilty of foul language.
Beyond mere simple English words, what I need like anyone else learning a foreign language, is examples in context, how to use such a word or phrase. What I try to do is to memorise a word or phrase and go and look for the context in which it is used, otherwise it would be an useless exercise in transcription and learning by heart something that you have not fully understood. In short, I need to know what I am learning and why. Having a broad spectrum of the language is something you acquire over time, with study, slowly you shift your focus and widen your view.
I must say, however, that the most difficult part, especially for us Italians with English, is the pronunciation. Our language is pronounced exactly as it is written, with the possible exception of the Latin diphthongs, which are really just a drop in the ocean now.
In any case, dialectal variations abound here as everywhere else in the world, and idioms evolve and do so on a 'traditional' cultural basis. Ours is averagely oriented towards food, misery, war, religion (though I am not particularly attracted to it), love, family.
And no shortage of professional blasphemers in certain regions who have, however, over time, refined their technique with very long turns to say the same thing but without being blasphemous (but not out of respect, just out of fear, haha)