English is a very tricky language. For any non-English speakers who are trying to learn English, the vagaries in spelling and pronunciation of our language must make it nearly incomprehensible. Unlike most of the Romance languages, the pronunciation of which is reliably predictable, English wanders all over the place. Look at the old “tomb, comb, bomb” problem. Why does the value of the “O” change from “oo” to “oh” to “ah?” Why does the “ough” in “tough, trough, through, though” go from “uff” to “off” to “oo” to “oh?” There are, of course, explanations, but those learning our language simply shake their heads and growl at the inconsistencies. And one of the strangest inconsistencies of all is the variety of spellings for the “ʃ” phoneme, partly accounted for by our tendency to borrow words and pronunciations from other languages.
And that's just the tip of the iceberg. We tend to make slang expressions permanent, and many of those expressions we make by adding adverbs to our verbs. Try explaining what we mean by "slow down" and "slow up" when both mean the same. Look at "shake up" and "shake down"; "knock off," "knock up," and "knock down"; "show off" and "show down"; "stick up" and "stuck up"; "strike out" and "strike up"; "show off," "show up," and "showdown"; or "chew out" and "shack up." And there's the whole remainder of the ice berg. And all our other slang words. Once we said of a sexy woman that she was hot. Now we say she's cool but she's not cold.
Good luck, English learners, good luck.