Something I find constantly amazing is how bad English is at differentiating crucially important words. For example, the numbers 'fifty' and 'fifteen' are almost identical. And in American English, 'can' and 'can't' are pretty hard to distinguish.
For the basic digits, the biggest problem is between 'nine' and 'five', both of which are monosyllables with the same /ai/ vowel. In air traffic control, people are instructed to say them as 'niner' (with two syllables) and 'fife' (devoicing the final consonant). Maybe that solves the problem, though away from air traffic control, most ordinary speakers do not follow this pattern.
It is interesting that Chinese does better: the digits that are confused are yi ('one') and qi ('seven'), because they both have the same vowel on the same high-level tone. But even ordinary folk usually know it is better to change yi into yao when reading out phone numbers. It is strange that English speakers generally don't know how to do something comparable with 'nine' and 'five'.
Even people working in air traffic control get into trouble with some English words. I just read a news report (here) about a pilot in the USA who landed his plane at the wrong airport partly, it seems, because he confused his hand-written 'west' with 'east'. It is stunning that we do not make these two terms maximally distinct instead of both having four letters ending with 'st'.
