English does not do this; every word has its own pronunciation, only loosely related to how it is spelled. I think every native English speaker has had the experience of learning a word from reading it, and subsequently mis-pronouncing it because we had to guess at the pronunciation. E.g. I suffered acute embarrassment from mis-pronouncing "Hermione" when talking to a friend about the Potter books. I grew up in the UK but had never met the name before and my guess at pronunciation was entirely reasonable but entirely wrong.
Though I lived for a while in Ireland, and they have it worse. My friend Mebd laughed at me a lot.
And if you pronounced [e] and [ɛ] to native speakers of either Spanish or Japanese, they most likely wouldn't be able to differentiate the two sounds consistently without having had training. I know that in Spanish, realization of e can be either vowel depending on the speaker and context; they might pronounce "tierra" as [tjɛra] and "mesa" as [mesa].
So, while I disagree that they sound "exactly the same", I do agree that in most cases the differences between [e] and [ɛ] wouldn't be enough to cause confusion between speakers of either language.
What's your source for this? Wikipedia says "/e, o/ are mid [e̞, o̞]" [1]
>The mid front unrounded vowel is a type of vowel sound that is used in some spoken languages. There is no dedicated symbol in the International Phonetic Alphabet that represents the exact mid front unrounded vowel between close-mid [e] and open-mid [ɛ], but it is normally written ⟨e⟩.
[1] https://en.wikipedia.org/wiki/Japanese_phonology?wprov=sfla1
I learn English since I was pretty young, I believe I'm quite fluent (I mostly use English for work, I lived for two years in an English speaking country, I read books in English, etc), and I still have problems distinguishing some English vowels. I think sound acquisition is one of the hardest things to learn for a non-native speaker.
I am a Spanish guy living in Japan, so I can confirm it. I didn't have any idea that the two sounds are supposed to be different because to me they sound exactly the same.
Fun fact: Japanese people are surprised that we have the same five vowels (although the U is a bit different), and that we can get the correct pronunciation very easily.